QGraphicsItem 类

QGraphicsItem 类是基类为所有图形项在 QGraphicsScene . 更多...

该类在 Qt 4.2 引入。

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详细描述

它为编写自己的自定义项提供轻量级基础。这包括定义项几何体、碰撞检测、绘制实现和项交互 (透过事件处理程序)。QGraphicsItem 属于 图形视图框架

为方便起见，Qt 为最常见形状提供了一组标准图形项。它们是：

• QGraphicsEllipseItem 提供椭圆项
• QGraphicsLineItem 提供线条项
• QGraphicsPathItem 提供任意路径项
• QGraphicsPixmapItem 提供像素图项
• QGraphicsPolygonItem 提供多边形项
• QGraphicsRectItem 提供矩形项
• QGraphicsSimpleTextItem 提供简单文本标签项
• QGraphicsTextItem 提供高级文本浏览器项

项的所有几何信息都基于其本地坐标系。项的位置 pos ()，是唯一未运转于本地坐标的函数，因为它按父级坐标返回位置。 图形视图坐标系 详细描述了坐标系。

可以设置项是否应该可见 (即：绘制和接受事件)，通过调用 setVisible (). Hiding an item will also hide its children. Similarly, you can enable or disable an item by calling setEnabled (). If you disable an item, all its children will also be disabled. By default, items are both visible and enabled. To toggle whether an item is selected or not, first enable selection by setting the ItemIsSelectable flag, and then call setSelected (). Normally, selection is toggled by the scene, as a result of user interaction.

To write your own graphics item, you first create a subclass of QGraphicsItem, and then start by implementing its two pure virtual public functions: boundingRect (), which returns an estimate of the area painted by the item, and paint (), which implements the actual painting. For example:

class SimpleItem : public QGraphicsItem
{
public:
    QRectF boundingRect() const override
    {
        qreal penWidth = 1;
        return QRectF(-10 - penWidth / 2, -10 - penWidth / 2,
                      20 + penWidth, 20 + penWidth);
    }
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
               QWidget *widget) override
    {
        painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
    }
};
					

The boundingRect () 函数有许多不同用途。 QGraphicsScene bases its item index on boundingRect ()，和 QGraphicsView uses it both for culling invisible items, and for determining the area that needs to be recomposed when drawing overlapping items. In addition, QGraphicsItem's collision detection mechanisms use boundingRect () to provide an efficient cut-off. The fine grained collision algorithm in collidesWithItem () is based on calling shape (), which returns an accurate outline of the item's shape as a QPainterPath .

QGraphicsScene 期望所有项 boundingRect () 和 shape () to remain unchanged unless it is notified. If you want to change an item's geometry in any way, you must first call prepareGeometryChange () to allow QGraphicsScene to update its bookkeeping.

碰撞检测可以按 2 种方式完成：

1. 重实现 shape () to return an accurate shape for your item, and rely on the default implementation of collidesWithItem () to do shape-shape intersection. This can be rather expensive if the shapes are complex.
2. 重实现 collidesWithItem () to provide your own custom item and shape collision algorithm.

The contains () 函数可以被调用以确定项是否 包含 a point or not. This function can also be reimplemented by the item. The default behavior of contains () is based on calling shape ().

Items can contain other items, and also be contained by other items. All items can have a parent item and a list of children. Unless the item has no parent, its position is in parent coordinates (i.e., the parent's local coordinates). Parent items propagate both their position and their transformation to all children.

变换

QGraphicsItem supports projective transformations in addition to its base position, pos (). There are several ways to change an item's transformation. For simple transformations, you can call either of the convenience functions setRotation () 或 setScale (), or you can pass any transformation matrix to setTransform (). For advanced transformation control you also have the option of setting several combined transformations by calling setTransformations ().

Item transformations accumulate from parent to child, so if both a parent and child item are rotated 90 degrees, the child's total transformation will be 180 degrees. Similarly, if the item's parent is scaled to 2x its original size, its children will also be twice as large. An item's transformation does not affect its own local geometry; all geometry functions (e.g., contains (), update (), and all the mapping functions) still operate in local coordinates. For convenience, QGraphicsItem provides the functions sceneTransform (), which returns the item's total transformation matrix (including its position and all parents' positions and transformations), and scenePos (), which returns its position in scene coordinates. To reset an item's matrix, call resetTransform ().

Certain transformation operations produce a different outcome depending on the order in which they are applied. For example, if you scale an transform, and then rotate it, you may get a different result than if the transform was rotated first. However, the order you set the transformation properties on QGraphicsItem does not affect the resulting transformation; QGraphicsItem always applies the properties in a fixed, defined order:

• 应用项的基变换 ( transform ())
• The item's transformations list is applied in order ( transformations ())
• The item is rotated relative to its transform origin point ( rotation (), transformOriginPoint ())
• The item is scaled relative to its transform origin point ( scale (), transformOriginPoint ())

描绘

The paint () 函数被调用通过 QGraphicsView 以描绘项内容。项没有背景 (或默认填充自身)；项后的任何内容会照射此功能未明确描绘的所有区域。可以调用 update () 以调度重新描绘，可选地传递需要重新描绘的矩形。根据项在视图中是否可见，项可能或可能不会被重新描绘；不存在等价对于 QWidget::repaint () 在 QGraphicsItem。

项由视图描绘，从父级项开始，然后绘制子级，按升序堆叠次序。可以设置项的堆叠次序通过调用 setZValue ()，和测试它通过调用 zValue ()，其中具有低 Z 值的项在具有高 Z 值的项之前被描绘。堆叠次序适用于同级项；父级始终在其子级之前绘制。

排序

所有项都是按照定义的、稳定次序绘制的，相同的次序决定哪些项将首先接受鼠标输入当点击场景时。通常不必担心排序，因为项遵循自然次序，遵循场景的逻辑结构。

项的子级堆叠在父级顶部，和同级项按插入次序 (即：按照将它们添加到场景或添加到同一父级的相同次序) 堆叠。若添加项 A，然后 B，那么 B 位于 A 顶部。若接着添加 C，则项的堆叠次序将是 A，然后是 B，接着是 C。

此范例展示机器人所有肢体的堆叠顺序，来自 拖放 Robot 范例。躯干是 root 项 (所有其它项都是躯干的子级或后代)，因此首先绘制它。接着，绘制头部，因为它是躯干子级列表中的第 1 项。然后，绘制左上臂。因为下臂是上臂的子级，绘制下臂，之后是上臂的下一同级 (右上臂)，依此类推。

对于高级用户，有一些方法能更改项如何排序：

• 可以调用 setZValue () 在项中以明确将其堆叠在其它同级项的顶部或下方。项的默认 Z 值为 0。具有相同 Z 值的项按插入次序堆叠。
• 可以调用 stackBefore () 以重新排序子级的列表。这将直接修改插入次序。
• 可以设置 ItemStacksBehindParent 标志以将子级项堆叠在其父级后面。

2 同级项的堆叠次序还计数每项的子级和后代项。因此，若一项在另一项之上，那么它的所有子级也在其它项的所有子级之上。

事件

QGraphicsItem 接收事件从 QGraphicsScene 透过虚函数 sceneEvent ()。此函数将最常见事件，分发给一组方便事件处理程序：

• contextMenuEvent () 处理上下文菜单事件
• focusInEvent () 和 focusOutEvent () 处理聚焦入和聚焦出事件
• hoverEnterEvent (), hoverMoveEvent ()，和 hoverLeaveEvent () 处理悬停进入、移动及离开事件
• inputMethodEvent () 处理输入事件，以获得可访问性支持
• keyPressEvent () 和 keyReleaseEvent () 处理键按下和释放事件
• mousePressEvent (), mouseMoveEvent (), mouseReleaseEvent ()，和 mouseDoubleClickEvent () 处理鼠标按下、移动、释放、点击和双击事件

可以过滤用于任何其它项的事件，通过安装事件过滤器。此功能独立于 Qt 常规事件过滤器 (见 QObject::installEventFilter ())，仅工作于子类化 QObject 。在将项安装作为另一项的事件过滤器后，通过调用 installSceneEventFilter ()，将收到被过滤事件，通过虚函数 sceneEventFilter ()。可以移除项事件过滤器通过调用 removeSceneEventFilter ().

自定义数据

Sometimes it's useful to register custom data with an item, be it a custom item, or a standard item. You can call setData () on any item to store data in it using a key-value pair (the key being an integer, and the value is a QVariant ). To get custom data from an item, call data (). This functionality is completely untouched by Qt itself; it is provided for the user's convenience.

另请参阅 QGraphicsScene , QGraphicsView ，和 图形视图框架 .

成员类型文档编制

enum QGraphicsItem:: CacheMode

此枚举描述 QGraphicsItem 's cache modes. Caching is used to speed up rendering by allocating and rendering to an off-screen pixel buffer, which can be reused when the item requires redrawing. For some paint devices, the cache is stored directly in graphics memory, which makes rendering very quick.

该枚举在 Qt 4.4 引入或被修改。

另请参阅 QGraphicsItem::setCacheMode ().

enum QGraphicsItem:: GraphicsItemChange

This enum describes the state changes that are notified by QGraphicsItem::itemChange (). The notifications are sent as the state changes, and in some cases, adjustments can be made (see the documentation for each change for details).

Note: Be careful with calling functions on the QGraphicsItem itself inside itemChange (), as certain function calls can lead to unwanted recursion. For example, you cannot call setPos () 在 itemChange () on an ItemPositionChange notification, as the setPos () function will again call itemChange (ItemPositionChange). Instead, you can return the new, adjusted position from itemChange ().

enum QGraphicsItem:: GraphicsItemFlag
flags QGraphicsItem:: GraphicsItemFlags

此枚举描述可以在项中设置的不同标志，以触发项行为的不同特征。

所有标志被禁用，默认情况下。

注意： This flag is similar to ItemContainsChildrenInShape but in addition enforces the containment by clipping the children.

注意： With this flag set you can still scale the item itself, and that scale transformation will influence the item's children.

注意： 若有设置此标志和 ItemClipsChildrenToShape 两者，将实施裁剪。这相当于仅仅设置 ItemClipsChildrenToShape。

该标志在 Qt 5.4 引入。

GraphicsItemFlags 类型是 typedef 对于 QFlags <GraphicsItemFlag>。它存储 GraphicsItemFlag 值的 OR 组合。

enum QGraphicsItem:: PanelModality

This enum specifies the behavior of a modal panel. A modal panel is one that blocks input to other panels. Note that items that are children of a modal panel are not blocked.

值是：

该枚举在 Qt 4.6 引入或被修改。

另请参阅 QGraphicsItem::setPanelModality (), QGraphicsItem::panelModality ()，和 QGraphicsItem::ItemIsPanel .

enum QGraphicsItem:: anonymous

值的返回通过虚拟 type () function in standard graphics item classes in Qt. All such standard graphics item classes in Qt are associated with a unique value for Type, e.g. the value returned by QGraphicsPathItem::type () is 2.

class QGraphicsPathItem : public QAbstractGraphicsShapeItem
{

public

:

enum

{ Type

=


2

};

int

type()

const

override {

return

Type; }

.


.


.

};
								

class CustomItem : public QGraphicsItem
{

public

:

enum

{ Type

=

UserType

+


1

};

int

type()

const

override
{

// Enable the use of qgraphicsitem_cast with this item.


return

Type;
}

.


.


.

};
								

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QGraphicsItem:: QGraphicsItem ( QGraphicsItem * parent = nullptr)

构造 QGraphicsItem 采用给定 parent 项。它不修改的父级对象返回通过 QObject::parent ().

若 parent is nullptr ，可以将项添加到场景通过调用 QGraphicsScene::addItem ()。然后，项将变为顶层项。

另请参阅 QGraphicsScene::addItem () 和 setParentItem ().

[虚拟] QGraphicsItem:: ~QGraphicsItem ()

销毁 QGraphicsItem and all its children. If this item is currently associated with a scene, the item will be removed from the scene before it is deleted.

注意： 它更高效为移除项从 QGraphicsScene 在销毁项之前。

bool QGraphicsItem:: acceptDrops () const

返回 true if this item can accept drag and drop events; otherwise, returns false . By default, items do not accept drag and drop events; items are transparent to drag and drop.

另请参阅 setAcceptDrops ().

bool QGraphicsItem:: acceptHoverEvents () const

返回 true 若项接受悬停事件 ( QGraphicsSceneHoverEvent )；否则，返回 false 。默认情况下，项不接受悬停事件。

该函数在 Qt 4.4 引入。

另请参阅 setAcceptHoverEvents () 和 setAcceptedMouseButtons ().

bool QGraphicsItem:: acceptTouchEvents () const

返回 true 若项接受 触摸事件 ；否则，返回 false 。默认情况下，项不接受触摸事件。

该函数在 Qt 4.6 引入。

另请参阅 setAcceptTouchEvents ().

Qt::MouseButtons QGraphicsItem:: acceptedMouseButtons () const

返回此项接受鼠标事件的鼠标按钮。默认情况下，接受所有鼠标按钮。

If an item accepts a mouse button, it will become the mouse grabber item when a mouse press event is delivered for that mouse button. However, if the item does not accept the button, QGraphicsScene will forward the mouse events to the first item beneath it that does.

另请参阅 setAcceptedMouseButtons () 和 mousePressEvent ().

[虚拟] void QGraphicsItem:: advance ( int phase )

所有项调用此虚函数 2 次通过 QGraphicsScene::advance () 槽。第 1 阶段，所有项被调用采用 phase == 0，指示场景中的项即将推进，然后所有项被调用采用 phase == 1。重实现此函数以更新项，若需要简单场景控制动画。

默认实现什么都不做。

This function is intended for animations. An alternative is to multiple-inherit from QObject and QGraphicsItem 和使用 动画框架 .

另请参阅 QGraphicsScene::advance () 和 QTimeLine .

[pure virtual] QRectF QGraphicsItem:: boundingRect () const

此纯虚函数以矩形形式定义项外部边界；所有描绘都必须限定到项边界矩形内。 QGraphicsView 使用这来确定项是否要求重新绘制。

尽管项的形状可以任意，但边界 rect 始终是矩形，且不受项变换的影响。

若想要改变项的边界矩形, 必须先调用 prepareGeometryChange ()。这通知场景即将发生变化，以便它可以更新其项的几何体索引；否则，场景未感知到项的新几何体，且结果未定义 (通常，渲染伪影仍留在视图中)。

重实现此函数让 QGraphicsView 确定 Widget 的哪些部分 (若有的话) 需要重新绘制。

注意：对于轮廓/描边的形状描绘而言，在边界矩形中包括钢笔宽度的一半很重要。但是，没有必要补偿抗锯齿。

范例：

QRectF CircleItem::boundingRect() const
{
    qreal penWidth = 1;
    return QRectF(-radius - penWidth / 2, -radius - penWidth / 2,
                  diameter + penWidth, diameter + penWidth);
}
					

另请参阅 boundingRegion (), shape (), contains (), 图形视图坐标系 ，和 prepareGeometryChange ().

QRegion QGraphicsItem:: boundingRegion (const QTransform & itemToDeviceTransform ) const

返回此项的边界区域。返回区域的坐标空间从属 itemToDeviceTransform 。若传递恒等 QTransform 作为参数，此函数将返回本地坐标区域。

The bounding region describes a coarse outline of the item's visual contents. Although it's expensive to calculate, it's also more precise than boundingRect (), and it can help to avoid unnecessary repainting when an item is updated. This is particularly efficient for thin items (e.g., lines or simple polygons). You can tune the granularity for the bounding region by calling setBoundingRegionGranularity (). The default granularity is 0; in which the item's bounding region is the same as its bounding rect.

itemToDeviceTransform is the transformation from item coordinates to device coordinates. If you want this function to return a QRegion in scene coordinates, you can pass sceneTransform () as an argument.

该函数在 Qt 4.4 引入。

另请参阅 boundingRegionGranularity ().

qreal QGraphicsItem:: boundingRegionGranularity () const

Returns the item's bounding region granularity; a value between and including 0 and 1. The default value is 0 (i.e., the lowest granularity, where the bounding region corresponds to the item's bounding rectangle).

该函数在 Qt 4.4 引入。

另请参阅 setBoundingRegionGranularity ().

QGraphicsItem::CacheMode QGraphicsItem:: cacheMode () const

Returns the cache mode for this item. The default mode is NoCache (i.e., cache is disabled and all painting is immediate).

该函数在 Qt 4.4 引入。

另请参阅 setCacheMode ().

QList < QGraphicsItem *> QGraphicsItem:: childItems () const

Returns a list of this item's children.

The items are sorted by stacking order. This takes into account both the items' insertion order and their Z-values.

该函数在 Qt 4.4 引入。

另请参阅 setParentItem (), zValue ()，和 排序 .

QRectF QGraphicsItem:: childrenBoundingRect () const

Returns the bounding rect of this item's descendants (i.e., its children, their children, etc.) in local coordinates. The rectangle will contain all descendants after they have been mapped to local coordinates. If the item has no children, this function returns an empty QRectF .

This does not include this item's own bounding rect; it only returns its descendants' accumulated bounding rect. If you need to include this item's bounding rect, you can add boundingRect () to childrenBoundingRect() using QRectF::operator|().

This function is linear in complexity; it determines the size of the returned bounding rect by iterating through all descendants.

另请参阅 boundingRect () 和 sceneBoundingRect ().

void QGraphicsItem:: clearFocus ()

从项获取键盘输入聚焦。

If it has focus, a 聚焦出事件 is sent to this item to tell it that it is about to lose the focus.

Only items that set the ItemIsFocusable flag, or widgets that set an appropriate focus policy, can accept keyboard focus.

另请参阅 setFocus (), hasFocus ()，和 QGraphicsWidget::focusPolicy .

QPainterPath QGraphicsItem:: clipPath () const

Returns this item's clip path, or an empty QPainterPath if this item is not clipped. The clip path constrains the item's appearance and interaction (i.e., restricts the area the item can draw within and receive events for).

You can enable clipping by setting the ItemClipsToShape or ItemClipsChildrenToShape flags. The item's clip path is calculated by intersecting all clipping ancestors' shapes. If the item sets ItemClipsToShape , the final clip is intersected with the item's own shape.

注意： Clipping introduces a performance penalty for all items involved; you should generally avoid using clipping if you can (e.g., if your items always draw inside boundingRect () 或 shape () boundaries, clipping is not necessary).

该函数在 Qt 4.5 引入。

另请参阅 isClipped (), shape ()，和 setFlags ().

[虚拟] bool QGraphicsItem:: collidesWithItem (const QGraphicsItem * other , Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

返回 true 若此项碰撞同 other ；否则返回 false .

The mode 被应用于 other , and the resulting shape or bounding rectangle is then compared to this item's shape. The default value for mode is Qt::IntersectsItemShape ; other collides with this item if it either intersects, contains, or is contained by this item's shape (see Qt::ItemSelectionMode 了解细节)。

The default implementation is based on shape intersection, and it calls shape () on both items. Because the complexity of arbitrary shape-shape intersection grows with an order of magnitude when the shapes are complex, this operation can be noticeably time-consuming. You have the option of reimplementing this function in a subclass of QGraphicsItem to provide a custom algorithm. This allows you to make use of natural constraints in the shapes of your own items, in order to improve the performance of the collision detection. For instance, two untransformed perfectly circular items' collision can be determined very efficiently by comparing their positions and radii.

Keep in mind that when reimplementing this function and calling shape () 或 boundingRect () 在 other , the returned coordinates must be mapped to this item's coordinate system before any intersection can take place.

另请参阅 contains () 和 shape ().

[虚拟] bool QGraphicsItem:: collidesWithPath (const QPainterPath & path , Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

返回 true 若此项碰撞同 path .

碰撞的确定是通过 mode 。默认值对于 mode is Qt::IntersectsItemShape ; path collides with this item if it either intersects, contains, or is contained by this item's shape.

Note that this function checks whether the item's shape or bounding rectangle (depending on mode ) is contained within path , and not whether path is contained within the items shape or bounding rectangle.

另请参阅 collidesWithItem (), contains ()，和 shape ().

QList < QGraphicsItem *> QGraphicsItem:: collidingItems ( Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const

返回同此项碰撞的所有项的列表。

The way collisions are detected is determined by applying mode to items that are compared to this item, i.e., each item's shape or bounding rectangle is checked against this item's shape. The default value for mode is Qt::IntersectsItemShape .

另请参阅 collidesWithItem ().

QGraphicsItem *QGraphicsItem:: commonAncestorItem (const QGraphicsItem * other ) const

Returns the closest common ancestor item of this item and other ，或 nullptr if either other is nullptr , or there is no common ancestor.

该函数在 Qt 4.4 引入。

另请参阅 isAncestorOf ().

[虚拟] bool QGraphicsItem:: contains (const QPointF & point ) const

返回 true if this item contains point , which is in local coordinates; otherwise, false is returned. It is most often called from QGraphicsView to determine what item is under the cursor, and for that reason, the implementation of this function should be as light-weight as possible.

By default, this function calls shape (), but you can reimplement it in a subclass to provide a (perhaps more efficient) implementation.

另请参阅 shape (), boundingRect ()，和 collidesWithPath ().

[virtual protected] void QGraphicsItem:: contextMenuEvent ( QGraphicsSceneContextMenuEvent * event )

This event handler can be reimplemented in a subclass to process context menu events. The event parameter contains details about the event to be handled.

If you ignore the event (i.e., by calling QEvent::ignore ()), event will propagate to any item beneath this item. If no items accept the event, it will be ignored by the scene and propagate to the view.

It's common to open a QMenu in response to receiving a context menu event. Example:

void CustomItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QMenu menu;
    QAction *removeAction = menu.addAction("Remove");
    QAction *markAction = menu.addAction("Mark");
    QAction *selectedAction = menu.exec(event->screenPos());
    // ...
}
					

默认实现忽略事件。

另请参阅 sceneEvent ().

QCursor QGraphicsItem:: cursor () const

Returns the current cursor shape for the item. The mouse cursor will assume this shape when it's over this item. See the 预定义光标对象列表 了解有用形状范围。

An editor item might want to use an I-beam cursor:

item->setCursor(Qt::IBeamCursor);
					

If no cursor has been set, the cursor of the item beneath is used.

另请参阅 setCursor (), hasCursor (), unsetCursor (), QWidget::cursor ，和 QGuiApplication::overrideCursor ().

QVariant QGraphicsItem:: data ( int key ) const

返回此项的自定义数据为键 key 作为 QVariant .

自定义项数据对于在任何项中存储任意特性很有用。范例：

static const int ObjectName = 0;
QGraphicsItem *item = scene.itemAt(100, 50);
if (item->data(ObjectName).toString().isEmpty()) {
    if (qgraphicsitem_cast<ButtonItem *>(item))
        item->setData(ObjectName, "Button");
}
					

Qt does not use this feature for storing data; it is provided solely for the convenience of the user.

另请参阅 setData ().

QTransform QGraphicsItem:: deviceTransform (const QTransform & viewportTransform ) const

Returns this item's device transformation matrix, using viewportTransform to map from scene to device coordinates. This matrix can be used to map coordinates and geometrical shapes from this item's local coordinate system to the viewport's (or any device's) coordinate system. To map coordinates from the viewport, you must first invert the returned matrix.

范例：

QGraphicsRectItem rect;
rect.setPos(100, 100);
rect.deviceTransform(view->viewportTransform()).map(QPointF(0, 0));
// returns the item's (0, 0) point in view's viewport coordinates
rect.deviceTransform(view->viewportTransform()).inverted().map(QPointF(100, 100));
// returns view's viewport's (100, 100) coordinate in item coordinates
					

This function is the same as combining this item's scene transform with the view's viewport transform, but it also understands the ItemIgnoresTransformations flag. The device transform can be used to do accurate coordinate mapping (and collision detection) for untransformable items.

该函数在 Qt 4.3 引入。

另请参阅 transform (), setTransform (), scenePos (), 图形视图坐标系 ，和 itemTransform ().

[virtual protected] void QGraphicsItem:: dragEnterEvent ( QGraphicsSceneDragDropEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive drag enter events for this item. Drag enter events are generated as the cursor enters the item's area.

By accepting the event (i.e., by calling QEvent::accept ()), the item will accept drop events, in addition to receiving drag move and drag leave. Otherwise, the event will be ignored and propagate to the item beneath. If the event is accepted, the item will receive a drag move event before control goes back to the event loop.

A common implementation of dragEnterEvent accepts or ignores event depending on the associated mime data in event 。范例：

CustomItem::CustomItem()
{
    setAcceptDrops(true);
    ...
}
void CustomItem::dragEnterEvent(QGraphicsSceneDragDropEvent *event)
{
    event->setAccepted(event->mimeData()->hasFormat("text/plain"));
}
					

Items do not receive drag and drop events by default; to enable this feature, call setAcceptDrops(true) .

默认实现什么都不做。

另请参阅 dropEvent (), dragMoveEvent ()，和 dragLeaveEvent ().

[virtual protected] void QGraphicsItem:: dragLeaveEvent ( QGraphicsSceneDragDropEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive drag leave events for this item. Drag leave events are generated as the cursor leaves the item's area. Most often you will not need to reimplement this function, but it can be useful for resetting state in your item (e.g., highlighting).

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

Items do not receive drag and drop events by default; to enable this feature, call setAcceptDrops(true) .

默认实现什么都不做。

另请参阅 dragEnterEvent (), dropEvent ()，和 dragMoveEvent ().

[virtual protected] void QGraphicsItem:: dragMoveEvent ( QGraphicsSceneDragDropEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive drag move events for this item. Drag move events are generated as the cursor moves around inside the item's area. Most often you will not need to reimplement this function; it is used to indicate that only parts of the item can accept drops.

调用 QEvent::ignore () 或 QEvent::accept () 在 event toggles whether or not the item will accept drops at the position from the event. By default, event is accepted, indicating that the item allows drops at the specified position.

Items do not receive drag and drop events by default; to enable this feature, call setAcceptDrops(true) .

默认实现什么都不做。

另请参阅 dropEvent (), dragEnterEvent ()，和 dragLeaveEvent ().

[virtual protected] void QGraphicsItem:: dropEvent ( QGraphicsSceneDragDropEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive drop events for this item. Items can only receive drop events if the last drag move event was accepted.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

Items do not receive drag and drop events by default; to enable this feature, call setAcceptDrops(true) .

默认实现什么都不做。

另请参阅 dragEnterEvent (), dragMoveEvent ()，和 dragLeaveEvent ().

qreal QGraphicsItem:: effectiveOpacity () const

返回此项的 effective opacity, which is between 0.0 (transparent) and 1.0 (opaque). This value is a combination of this item's local opacity, and its parent and ancestors' opacities. The effective opacity decides how the item is rendered.

该函数在 Qt 4.5 引入。

另请参阅 opacity (), setOpacity (), paint (), ItemIgnoresParentOpacity ，和 ItemDoesntPropagateOpacityToChildren .

void QGraphicsItem:: ensureVisible (const QRectF & rect = QRectF(), int xmargin = 50, int ymargin = 50)

若此项是场景的一部分，查看通过 QGraphicsView ，此方便函数将试图卷动视图以确保 rect 在视图的视口中可见。若 rect 是 null 矩形 (默认)， QGraphicsItem 将默认为项的边界矩形。 xmargin and ymargin 是视图应该用于边距的像素数。

若无法到达指定矩形，内容卷动到最近有效位置。

若此项的查看不是通过 QGraphicsView ，此函数什么都不做。

另请参阅 QGraphicsView::ensureVisible ().

void QGraphicsItem:: ensureVisible ( qreal x , qreal y , qreal w , qreal h , int xmargin = 50, int ymargin = 50)

This convenience function is equivalent to calling ensureVisible( QRectF ( x , y , w , h ), xmargin , ymargin ).

bool QGraphicsItem:: filtersChildEvents () const

返回 true if this item filters child events (i.e., all events intended for any of its children are instead sent to this item); otherwise, false is returned.

The default value is false; child events are not filtered.

该函数在 Qt 4.6 引入。

另请参阅 setFiltersChildEvents ().

QGraphicsItem::GraphicsItemFlags QGraphicsItem:: flags () const

Returns this item's flags. The flags describe what configurable features of the item are enabled and not. For example, if the flags include ItemIsFocusable , the item can accept input focus.

By default, no flags are enabled.

另请参阅 setFlags () 和 setFlag ().

[virtual protected] void QGraphicsItem:: focusInEvent ( QFocusEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive focus in events for this item. The default implementation calls ensureVisible ().

另请参阅 focusOutEvent (), sceneEvent ()，和 setFocus ().

QGraphicsItem *QGraphicsItem:: focusItem () const

If this item, a child or descendant of this item currently has input focus, this function will return a pointer to that item. If no descendant has input focus, nullptr 被返回。

该函数在 Qt 4.6 引入。

另请参阅 hasFocus (), setFocus ()，和 QWidget::focusWidget ().

[virtual protected] void QGraphicsItem:: focusOutEvent ( QFocusEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive focus out events for this item. The default implementation does nothing.

另请参阅 focusInEvent (), sceneEvent ()，和 setFocus ().

QGraphicsItem *QGraphicsItem:: focusProxy () const

Returns this item's focus proxy, or nullptr if this item has no focus proxy.

该函数在 Qt 4.6 引入。

另请参阅 setFocusProxy (), setFocus ()，和 hasFocus ().

void QGraphicsItem:: grabKeyboard ()

抓取键盘输入。

The item will receive all keyboard input to the scene until one of the following events occur:

• The item becomes invisible
• The item is removed from the scene
• The item is deleted
• The item calls ungrabKeyboard ()
• Another item calls grabKeyboard(); the item will regain the keyboard grab when the other item calls ungrabKeyboard ().

When an item gains the keyboard grab, it receives a QEvent::GrabKeyboard event. When it loses the keyboard grab, it receives a QEvent::UngrabKeyboard event. These events can be used to detect when your item gains or loses the keyboard grab through other means than gaining input focus.

It is almost never necessary to explicitly grab the keyboard in Qt, as Qt grabs and releases it sensibly. In particular, Qt grabs the keyboard when your item gains input focus, and releases it when your item loses input focus, or when the item is hidden.

Note that only visible items can grab keyboard input. Calling grabKeyboard() on an invisible item has no effect.

Keyboard events are not affected.

该函数在 Qt 4.4 引入。

另请参阅 ungrabKeyboard (), grabMouse ()，和 setFocus ().

void QGraphicsItem:: grabMouse ()

抓取鼠标输入。

This item will receive all mouse events for the scene until any of the following events occurs:

• The item becomes invisible
• The item is removed from the scene
• The item is deleted
• The item call ungrabMouse ()
• Another item calls grabMouse(); the item will regain the mouse grab when the other item calls ungrabMouse ().

When an item gains the mouse grab, it receives a QEvent::GrabMouse event. When it loses the mouse grab, it receives a QEvent::UngrabMouse event. These events can be used to detect when your item gains or loses the mouse grab through other means than receiving mouse button events.

It is almost never necessary to explicitly grab the mouse in Qt, as Qt grabs and releases it sensibly. In particular, Qt grabs the mouse when you press a mouse button, and keeps the mouse grabbed until you release the last mouse button. Also, Qt::Popup widgets implicitly call grabMouse() when shown, and ungrabMouse () when hidden.

Note that only visible items can grab mouse input. Calling grabMouse() on an invisible item has no effect.

Keyboard events are not affected.

该函数在 Qt 4.4 引入。

另请参阅 QGraphicsScene::mouseGrabberItem (), ungrabMouse ()，和 grabKeyboard ().

QGraphicsEffect *QGraphicsItem:: graphicsEffect () const

Returns a pointer to this item's effect if it has one; otherwise nullptr .

该函数在 Qt 4.6 引入。

另请参阅 setGraphicsEffect ().

QGraphicsItemGroup *QGraphicsItem:: group () const

Returns a pointer to this item's item group, or nullptr if this item is not member of a group.

另请参阅 setGroup (), QGraphicsItemGroup ，和 QGraphicsScene::createItemGroup ().

bool QGraphicsItem:: hasCursor () const

返回 true if this item has a cursor set; otherwise, false is returned.

By default, items don't have any cursor set. cursor () will return a standard pointing arrow cursor.

另请参阅 unsetCursor ().

bool QGraphicsItem:: hasFocus () const

返回 true 若此项活动，且它或其 聚焦代理 拥有键盘输入聚焦；否则，返回 false .

另请参阅 focusItem (), setFocus (), QGraphicsScene::setFocusItem ()，和 isActive ().

void QGraphicsItem:: hide ()

隐藏项 (项默认可见)。

此方便函数相当于调用 setVisible(false) .

另请参阅 show () 和 setVisible ().

[virtual protected] void QGraphicsItem:: hoverEnterEvent ( QGraphicsSceneHoverEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive hover enter events for this item. The default implementation calls update (); otherwise it does nothing.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

另请参阅 hoverMoveEvent (), hoverLeaveEvent (), sceneEvent ()，和 setAcceptHoverEvents ().

[virtual protected] void QGraphicsItem:: hoverLeaveEvent ( QGraphicsSceneHoverEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive hover leave events for this item. The default implementation calls update (); otherwise it does nothing.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

另请参阅 hoverEnterEvent (), hoverMoveEvent (), sceneEvent ()，和 setAcceptHoverEvents ().

[virtual protected] void QGraphicsItem:: hoverMoveEvent ( QGraphicsSceneHoverEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive hover move events for this item. The default implementation does nothing.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

另请参阅 hoverEnterEvent (), hoverLeaveEvent (), sceneEvent ()，和 setAcceptHoverEvents ().

[virtual protected] void QGraphicsItem:: inputMethodEvent ( QInputMethodEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive input method events for this item. The default implementation ignores the event.

另请参阅 inputMethodQuery () 和 sceneEvent ().

Qt::InputMethodHints QGraphicsItem:: inputMethodHints () const

Returns the current input method hints of this item.

Input method hints are only relevant for input items. The hints are used by the input method to indicate how it should operate. For example, if the Qt::ImhNumbersOnly flag is set, the input method may change its visual components to reflect that only numbers can be entered.

The effect may vary between input method implementations.

该函数在 Qt 4.6 引入。

另请参阅 setInputMethodHints () 和 inputMethodQuery ().

[virtual protected] QVariant QGraphicsItem:: inputMethodQuery ( Qt::InputMethodQuery query ) const

This method is only relevant for input items. It is used by the input method to query a set of properties of the item to be able to support complex input method operations, such as support for surrounding text and reconversions. query 指定查询特性。

另请参阅 inputMethodEvent () 和 QInputMethodEvent .

void QGraphicsItem:: installSceneEventFilter ( QGraphicsItem * filterItem )

Installs an event filter for this item on filterItem , causing all events for this item to first pass through filterItem 's sceneEventFilter () 函数。

To filter another item's events, install this item as an event filter for the other item. Example:

QGraphicsScene scene;
QGraphicsEllipseItem *ellipse = scene.addEllipse(QRectF(-10, -10, 20, 20));
QGraphicsLineItem *line = scene.addLine(QLineF(-10, -10, 20, 20));
line->installSceneEventFilter(ellipse);
// line's events are filtered by ellipse's sceneEventFilter() function.
ellipse->installSceneEventFilter(line);
// ellipse's events are filtered by line's sceneEventFilter() function.
					

An item can only filter events for other items in the same scene. Also, an item cannot filter its own events; instead, you can reimplement sceneEvent () 直接。

Items must belong to a scene for scene event filters to be installed and used.

另请参阅 removeSceneEventFilter (), sceneEventFilter ()，和 sceneEvent ().

bool QGraphicsItem:: isActive () const

返回 true if this item is active; otherwise returns false .

An item can only be active if the scene is active. An item is active if it is, or is a descendent of, an active panel. Items in non-active panels are not active.

Items that are not part of a panel follow scene activation when the scene has no active panel.

Only active items can gain input focus.

该函数在 Qt 4.6 引入。

另请参阅 QGraphicsScene::isActive (), QGraphicsScene::activePanel (), panel ()，和 isPanel ().

bool QGraphicsItem:: isAncestorOf (const QGraphicsItem * child ) const

返回 true if this item is an ancestor of child (i.e., if this item is child 's parent, or one of child 's parent's ancestors).

另请参阅 parentItem ().

bool QGraphicsItem:: isBlockedByModalPanel ( QGraphicsItem ** blockingPanel = nullptr) const

返回 true if this item is blocked by a modal panel, false otherwise. If blockingPanel is non-zero, blockingPanel will be set to the modal panel that is blocking this item. If this item is not blocked, blockingPanel will not be set by this function.

This function always returns false for items not in a scene.

该函数在 Qt 4.6 引入。

另请参阅 panelModality (), setPanelModality ()，和 PanelModality .

bool QGraphicsItem:: isClipped () const

返回 true if this item is clipped. An item is clipped if it has either set the ItemClipsToShape flag, or if it or any of its ancestors has set the ItemClipsChildrenToShape 标志。

Clipping affects the item's appearance (i.e., painting), as well as mouse and hover event delivery.

另请参阅 clipPath (), shape ()，和 setFlags ().

bool QGraphicsItem:: isEnabled () const

返回 true if the item is enabled; otherwise, false is returned.

另请参阅 setEnabled ().

bool QGraphicsItem:: isObscured (const QRectF & rect = QRectF()) const

这是重载函数。

返回 true if rect is completely obscured by the opaque shape of any of colliding items above it (i.e., with a higher Z value than this item).

该函数在 Qt 4.3 引入。

另请参阅 opaqueArea ().

bool QGraphicsItem:: isObscured ( qreal x , qreal y , qreal w , qreal h ) const

这是重载函数。

This convenience function is equivalent to calling isObscured( QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

[虚拟] bool QGraphicsItem:: isObscuredBy (const QGraphicsItem * item ) const

返回 true if this item's bounding rect is completely obscured by the opaque shape of item .

The base implementation maps item 's opaqueArea () to this item's coordinate system, and then checks if this item's boundingRect () is fully contained within the mapped shape.

You can reimplement this function to provide a custom algorithm for determining whether this item is obscured by item .

另请参阅 opaqueArea () 和 isObscured ().

bool QGraphicsItem:: isPanel () const

返回 true 若项是面板；否则返回 false .

该函数在 Qt 4.6 引入。

另请参阅 QGraphicsItem::panel () 和 ItemIsPanel .

bool QGraphicsItem:: isSelected () const

返回 true if this item is selected; otherwise, false is returned.

Items that are in a group inherit the group's selected state.

Items are not selected by default.

另请参阅 setSelected () 和 QGraphicsScene::setSelectionArea ().

bool QGraphicsItem:: isUnderMouse () const

返回 true if this item is currently under the mouse cursor in one of the views; otherwise, false is returned.

该函数在 Qt 4.4 引入。

另请参阅 QGraphicsScene::views () 和 QCursor::pos ().

bool QGraphicsItem:: isVisible () const

返回 true if the item is visible; otherwise, false is returned.

Note that the item's general visibility is unrelated to whether or not it is actually being visualized by a QGraphicsView .

另请参阅 setVisible ().

bool QGraphicsItem:: isVisibleTo (const QGraphicsItem * parent ) const

返回 true if the item is visible to parent ; otherwise, false is returned. parent 可以是 nullptr , in which case this function will return whether the item is visible to the scene or not.

An item may not be visible to its ancestors even if isVisible () is true. It may also be visible to its ancestors even if isVisible () is false. If any ancestor is hidden, the item itself will be implicitly hidden, in which case this function will return false.

该函数在 Qt 4.4 引入。

另请参阅 isVisible () 和 setVisible ().

bool QGraphicsItem:: isWidget () const

返回 true if this item is a widget (i.e., QGraphicsWidget )；否则，返回 false .

该函数在 Qt 4.4 引入。

bool QGraphicsItem:: isWindow () const

返回 true if the item is a QGraphicsWidget window, otherwise returns false.

该函数在 Qt 4.4 引入。

另请参阅 QGraphicsWidget::windowFlags ().

[virtual protected] QVariant QGraphicsItem:: itemChange ( QGraphicsItem::GraphicsItemChange change , const QVariant & value )

此虚函数被调用由 QGraphicsItem to notify custom items that some part of the item's state changes. By reimplementing this function, you can react to a change, and in some cases (depending on change ), adjustments can be made.

change is the parameter of the item that is changing. value is the new value; the type of the value depends on change .

范例：

QVariant Component::itemChange(GraphicsItemChange change, const QVariant &value)
{
    if (change == ItemPositionChange && scene()) {
        // value is the new position.
        QPointF newPos = value.toPointF();
        QRectF rect = scene()->sceneRect();
        if (!rect.contains(newPos)) {
            // Keep the item inside the scene rect.
            newPos.setX(qMin(rect.right(), qMax(newPos.x(), rect.left())));
            newPos.setY(qMin(rect.bottom(), qMax(newPos.y(), rect.top())));
            return newPos;
        }
    }
    return QGraphicsItem::itemChange(change, value);
}
					

默认实现什么都不做，并返回 value .

注意：某些 QGraphicsItem functions cannot be called in a reimplementation of this function; see the GraphicsItemChange 文档编制了解细节。

另请参阅 GraphicsItemChange .

QTransform QGraphicsItem:: itemTransform (const QGraphicsItem * other , bool * ok = nullptr) const

返回 QTransform that maps coordinates from this item to other 。若 ok is not null, and if there is no such transform, the boolean pointed to by ok will be set to false; otherwise it will be set to true.

This transform provides an alternative to the mapToItem () 或 mapFromItem () functions, by returning the appropriate transform so that you can map shapes and coordinates yourself. It also helps you write more efficient code when repeatedly mapping between the same two items.

注意： In rare circumstances, there is no transform that maps between two items.

该函数在 Qt 4.5 引入。

另请参阅 mapToItem (), mapFromItem ()，和 deviceTransform ().

[virtual protected] void QGraphicsItem:: keyPressEvent ( QKeyEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive key press events for this item. The default implementation ignores the event. If you reimplement this handler, the event will by default be accepted.

Note that key events are only received for items that set the ItemIsFocusable flag, and that have keyboard input focus.

另请参阅 keyReleaseEvent (), setFocus (), QGraphicsScene::setFocusItem ()，和 sceneEvent ().

[virtual protected] void QGraphicsItem:: keyReleaseEvent ( QKeyEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive key release events for this item. The default implementation ignores the event. If you reimplement this handler, the event will by default be accepted.

Note that key events are only received for items that set the ItemIsFocusable flag, and that have keyboard input focus.

另请参阅 keyPressEvent (), setFocus (), QGraphicsScene::setFocusItem ()，和 sceneEvent ().

QPointF QGraphicsItem:: mapFromItem (const QGraphicsItem * item , const QPointF & point ) const

映射点 point , which is in item 's coordinate system, to this item's coordinate system, and returns the mapped coordinate.

若 item is nullptr , this function returns the same as mapFromScene ().

另请参阅 itemTransform (), mapFromParent (), mapFromScene (), transform (), mapToItem ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromItem (const QGraphicsItem * item , const QRectF & rect ) const

映射矩形 rect , which is in item 's coordinate system, to this item's coordinate system, and returns the mapped rectangle as a polygon.

若 item is nullptr , this function returns the same as mapFromScene ()

另请参阅 itemTransform (), mapToItem (), mapFromParent (), transform ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromItem (const QGraphicsItem * item , const QPolygonF & polygon ) const

映射多边形 polygon , which is in item 's coordinate system, to this item's coordinate system, and returns the mapped polygon.

若 item is nullptr , this function returns the same as mapFromScene ().

另请参阅 itemTransform (), mapToItem (), mapFromParent (), transform ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapFromItem (const QGraphicsItem * item , const QPainterPath & path ) const

映射路径 path , which is in item 's coordinate system, to this item's coordinate system, and returns the mapped path.

若 item is nullptr , this function returns the same as mapFromScene ().

另请参阅 itemTransform (), mapFromParent (), mapFromScene (), mapToItem ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapFromItem (const QGraphicsItem * item , qreal x , qreal y ) const

这是重载函数。

此方便函数相当于调用 mapFromItem( item , QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapFromItem (const QGraphicsItem * item , qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapFromItem(item, QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

QPointF QGraphicsItem:: mapFromParent (const QPointF & point ) const

映射点 point , which is in this item's parent's coordinate system, to this item's coordinate system, and returns the mapped coordinate.

另请参阅 mapFromItem (), mapFromScene (), transform (), mapToParent ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromParent (const QRectF & rect ) const

映射矩形 rect , which is in this item's parent's coordinate system, to this item's coordinate system, and returns the mapped rectangle as a polygon.

另请参阅 mapToParent (), mapFromItem (), transform ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromParent (const QPolygonF & polygon ) const

映射多边形 polygon , which is in this item's parent's coordinate system, to this item's coordinate system, and returns the mapped polygon.

另请参阅 mapToParent (), mapToItem (), transform ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapFromParent (const QPainterPath & path ) const

映射路径 path , which is in this item's parent's coordinate system, to this item's coordinate system, and returns the mapped path.

另请参阅 mapFromScene (), mapFromItem (), mapToParent ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapFromParent ( qreal x , qreal y ) const

这是重载函数。

This convenience function is equivalent to calling mapFromParent( QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapFromParent ( qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapFromItem ( QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

QPointF QGraphicsItem:: mapFromScene (const QPointF & point ) const

映射点 point , which is in this item's scene's coordinate system, to this item's coordinate system, and returns the mapped coordinate.

另请参阅 mapFromItem (), mapFromParent (), transform (), mapToScene ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromScene (const QRectF & rect ) const

映射矩形 rect , which is in this item's scene's coordinate system, to this item's coordinate system, and returns the mapped rectangle as a polygon.

另请参阅 mapToScene (), mapFromItem (), transform ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapFromScene (const QPolygonF & polygon ) const

映射多边形 polygon , which is in this item's scene's coordinate system, to this item's coordinate system, and returns the mapped polygon.

另请参阅 mapToScene (), mapFromParent (), transform ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapFromScene (const QPainterPath & path ) const

映射路径 path , which is in this item's scene's coordinate system, to this item's coordinate system, and returns the mapped path.

另请参阅 mapFromParent (), mapFromItem (), mapToScene ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapFromScene ( qreal x , qreal y ) const

这是重载函数。

此方便函数相当于调用 mapFromScene( QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapFromScene ( qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapFromScene( QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

QRectF QGraphicsItem:: mapRectFromItem (const QGraphicsItem * item , const QRectF & rect ) const

映射矩形 rect , which is in item 's coordinate system, to this item's coordinate system, and returns the mapped rectangle as a new rectangle (i.e., the bounding rectangle of the resulting polygon).

若 item is nullptr , this function returns the same as mapRectFromScene ().

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectFromItem (const QGraphicsItem * item , qreal x , qreal y , qreal w , qreal h ) const

This convenience function is equivalent to calling mapRectFromItem(item, QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QRectF QGraphicsItem:: mapRectFromParent (const QRectF & rect ) const

映射矩形 rect , which is in this item's parent's coordinate system, to this item's coordinate system, and returns the mapped rectangle as a new rectangle (i.e., the bounding rectangle of the resulting polygon).

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectFromParent ( qreal x , qreal y , qreal w , qreal h ) const

This convenience function is equivalent to calling mapRectFromParent( QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QRectF QGraphicsItem:: mapRectFromScene (const QRectF & rect ) const

映射矩形 rect , which is in scene coordinates, to this item's coordinate system, and returns the mapped rectangle as a new rectangle (i.e., the bounding rectangle of the resulting polygon).

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectFromScene ( qreal x , qreal y , qreal w , qreal h ) const

This convenience function is equivalent to calling mapRectFromScene( QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QRectF QGraphicsItem:: mapRectToItem (const QGraphicsItem * item , const QRectF & rect ) const

映射矩形 rect ，从此项的坐标系到 item 's coordinate system, and returns the mapped rectangle as a new rectangle (i.e., the bounding rectangle of the resulting polygon).

若 item is nullptr , this function returns the same as mapRectToScene ().

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectToItem (const QGraphicsItem * item , qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapRectToItem(item, QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QRectF QGraphicsItem:: mapRectToParent (const QRectF & rect ) const

映射矩形 rect , which is in this item's coordinate system, to its parent's coordinate system, and returns the mapped rectangle as a new rectangle (i.e., the bounding rectangle of the resulting polygon).

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectToParent ( qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapRectToParent( QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QRectF QGraphicsItem:: mapRectToScene (const QRectF & rect ) const

映射矩形 rect ，从此项的坐标系到场景坐标系，并将映射矩形作为新矩形 (即：结果多边形的边界矩形) 返回。

该函数在 Qt 4.5 引入。

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QRectF QGraphicsItem:: mapRectToScene ( qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapRectToScene( QRectF ( x , y , w , h )).

该函数在 Qt 4.5 引入。

QPointF QGraphicsItem:: mapToItem (const QGraphicsItem * item , const QPointF & point ) const

映射点 point ，从此项的坐标系到 item 的坐标系，并返回映射坐标。

若 item is nullptr , this function returns the same as mapToScene ().

另请参阅 itemTransform (), mapToParent (), mapToScene (), transform (), mapFromItem ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToItem (const QGraphicsItem * item , const QRectF & rect ) const

映射矩形 rect ，从此项的坐标系到 item 's coordinate system, and returns the mapped rectangle as a polygon.

若 item is nullptr , this function returns the same as mapToScene ().

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToItem (const QGraphicsItem * item , const QPolygonF & polygon ) const

映射多边形 polygon ，从此项的坐标系到 item 's coordinate system, and returns the mapped polygon.

若 item is nullptr , this function returns the same as mapToScene ().

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapToItem (const QGraphicsItem * item , const QPainterPath & path ) const

映射路径 path ，从此项的坐标系到 item 's coordinate system, and returns the mapped path.

若 item is nullptr , this function returns the same as mapToScene ().

另请参阅 itemTransform (), mapToParent (), mapToScene (), mapFromItem ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapToItem (const QGraphicsItem * item , qreal x , qreal y ) const

这是重载函数。

This convenience function is equivalent to calling mapToItem( item , QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapToItem (const QGraphicsItem * item , qreal x , qreal y , qreal w , qreal h ) const

This convenience function is equivalent to calling mapToItem(item, QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

QPointF QGraphicsItem:: mapToParent (const QPointF & point ) const

映射点 point , which is in this item's coordinate system, to its parent's coordinate system, and returns the mapped coordinate. If the item has no parent, point will be mapped to the scene's coordinate system.

另请参阅 mapToItem (), mapToScene (), transform (), mapFromParent ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToParent (const QRectF & rect ) const

映射矩形 rect , which is in this item's coordinate system, to its parent's coordinate system, and returns the mapped rectangle as a polygon. If the item has no parent, rect will be mapped to the scene's coordinate system.

另请参阅 mapToScene (), mapToItem (), mapFromParent ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToParent (const QPolygonF & polygon ) const

映射多边形 polygon , which is in this item's coordinate system, to its parent's coordinate system, and returns the mapped polygon. If the item has no parent, polygon will be mapped to the scene's coordinate system.

另请参阅 mapToScene (), mapToItem (), mapFromParent ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapToParent (const QPainterPath & path ) const

映射路径 path , which is in this item's coordinate system, to its parent's coordinate system, and returns the mapped path. If the item has no parent, path will be mapped to the scene's coordinate system.

另请参阅 mapToScene (), mapToItem (), mapFromParent ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapToParent ( qreal x , qreal y ) const

这是重载函数。

This convenience function is equivalent to calling mapToParent( QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapToParent ( qreal x , qreal y , qreal w , qreal h ) const

This convenience function is equivalent to calling mapToParent( QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

QPointF QGraphicsItem:: mapToScene (const QPointF & point ) const

映射点 point , which is in this item's coordinate system, to the scene's coordinate system, and returns the mapped coordinate.

另请参阅 mapToItem (), mapToParent (), transform (), mapFromScene ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToScene (const QRectF & rect ) const

映射矩形 rect , which is in this item's coordinate system, to the scene's coordinate system, and returns the mapped rectangle as a polygon.

另请参阅 mapToParent (), mapToItem (), mapFromScene ()，和 图形视图坐标系 .

QPolygonF QGraphicsItem:: mapToScene (const QPolygonF & polygon ) const

映射多边形 polygon , which is in this item's coordinate system, to the scene's coordinate system, and returns the mapped polygon.

另请参阅 mapToParent (), mapToItem (), mapFromScene ()，和 图形视图坐标系 .

QPainterPath QGraphicsItem:: mapToScene (const QPainterPath & path ) const

映射路径 path , which is in this item's coordinate system, to the scene's coordinate system, and returns the mapped path.

另请参阅 mapToParent (), mapToItem (), mapFromScene ()，和 图形视图坐标系 .

QPointF QGraphicsItem:: mapToScene ( qreal x , qreal y ) const

这是重载函数。

此方便函数相当于调用 mapToScene( QPointF ( x , y )).

QPolygonF QGraphicsItem:: mapToScene ( qreal x , qreal y , qreal w , qreal h ) const

此方便函数相当于调用 mapToScene( QRectF ( x , y , w , h )).

该函数在 Qt 4.3 引入。

[virtual protected] void QGraphicsItem:: mouseDoubleClickEvent ( QGraphicsSceneMouseEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive mouse double-click events for this item.

When doubleclicking an item, the item will first receive a mouse press event, followed by a release event (i.e., a click), then a double-click event, and finally a release event.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

默认实现调用 mousePressEvent (). If you want to keep the base implementation when reimplementing this function, call QGraphicsItem::mouseDoubleClickEvent() in your reimplementation.

Note that an item will not receive double click events if it is neither selectable nor movable (single mouse clicks are ignored in this case, and that stops the generation of double clicks).

另请参阅 mousePressEvent (), mouseMoveEvent (), mouseReleaseEvent ()，和 sceneEvent ().

[virtual protected] void QGraphicsItem:: mouseMoveEvent ( QGraphicsSceneMouseEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive mouse move events for this item. If you do receive this event, you can be certain that this item also received a mouse press event, and that this item is the current mouse grabber.

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

The default implementation handles basic item interaction, such as selection and moving. If you want to keep the base implementation when reimplementing this function, call QGraphicsItem::mouseMoveEvent() in your reimplementation.

请注意 mousePressEvent () decides which graphics item it is that receives mouse events. See the mousePressEvent () description for details.

另请参阅 mousePressEvent (), mouseReleaseEvent (), mouseDoubleClickEvent ()，和 sceneEvent ().

[virtual protected] void QGraphicsItem:: mousePressEvent ( QGraphicsSceneMouseEvent * event )

此事件处理程序用于事件 event , can be reimplemented to receive mouse press events for this item. Mouse press events are only delivered to items that accept the mouse button that is pressed. By default, an item accepts all mouse buttons, but you can change this by calling setAcceptedMouseButtons ().

The mouse press event decides which item should become the mouse grabber (see QGraphicsScene::mouseGrabberItem ()). If you do not reimplement this function, the press event will propagate to any topmost item beneath this item, and no other mouse events will be delivered to this item.

If you do reimplement this function, event will by default be accepted (see QEvent::accept ()), and this item is then the mouse grabber. This allows the item to receive future move, release and double-click events. If you call QEvent::ignore () 在 event , this item will lose the mouse grab, and event will propagate to any topmost item beneath. No further mouse events will be delivered to this item unless a new mouse press event is received.

The default implementation handles basic item interaction, such as selection and moving. If you want to keep the base implementation when reimplementing this function, call QGraphicsItem::mousePressEvent() in your reimplementation.

事件 QEvent::ignore ()d for items that are neither movable nor selectable .

另请参阅 mouseMoveEvent (), mouseReleaseEvent (), mouseDoubleClickEvent ()，和 sceneEvent ().

[virtual protected] void QGraphicsItem:: mouseReleaseEvent ( QGraphicsSceneMouseEvent * event )

此事件处理程序用于事件 event ，可以重实现以接收此项的鼠标释放事件。

调用 QEvent::ignore () 或 QEvent::accept () 在 event 不起作用。

The default implementation handles basic item interaction, such as selection and moving. If you want to keep the base implementation when reimplementing this function, call QGraphicsItem::mouseReleaseEvent() in your reimplementation.

请注意 mousePressEvent () decides which graphics item it is that receives mouse events. See the mousePressEvent () description for details.

另请参阅 mousePressEvent (), mouseMoveEvent (), mouseDoubleClickEvent ()，和 sceneEvent ().

void QGraphicsItem:: moveBy ( qreal dx , qreal dy )

移动项通过 dx 水平点，和 dy 垂直点。此函数相当于调用 setPos ( pos () + QPointF ( dx , dy )).

qreal QGraphicsItem:: opacity () const

Returns this item's local opacity, which is between 0.0 (transparent) and 1.0 (opaque). This value is combined with parent and ancestor values into the effectiveOpacity (). The effective opacity decides how the item is rendered and also affects its visibility when queried by functions such as QGraphicsView::items ().

The opacity property decides the state of the painter passed to the paint () function. If the item is cached, i.e., ItemCoordinateCache or DeviceCoordinateCache , the effective property will be applied to the item's cache as it is rendered.

不透明度默认为 1.0；完全不透明。

该函数在 Qt 4.5 引入。

另请参阅 setOpacity (), paint (), ItemIgnoresParentOpacity ，和 ItemDoesntPropagateOpacityToChildren .

[虚拟] QPainterPath QGraphicsItem:: opaqueArea () const

此虚函数返回表示此项不透明区域的形状。区域是不透明的，若使用不透明笔刷或颜色 (即：不透明) 填充区域。

此函数用于 isObscuredBy (), which is called by underlying items to determine if they are obscured by this item.

The default implementation returns an empty QPainterPath , indicating that this item is completely transparent and does not obscure any other items.

另请参阅 isObscuredBy (), isObscured ()，和 shape ().

[pure virtual] void QGraphicsItem:: paint ( QPainter * painter , const QStyleOptionGraphicsItem * option , QWidget * widget = 0)

此函数通常被调用通过 QGraphicsView , paints the contents of an item in local coordinates.

Reimplement this function in a QGraphicsItem subclass to provide the item's painting implementation, using painter 。 option parameter provides style options for the item, such as its state, exposed area and its level-of-detail hints. The widget argument is optional. If provided, it points to the widget that is being painted on; otherwise, it is 0. For cached painting, widget is always 0.

void RoundRectItem::paint(QPainter *painter,
                          const QStyleOptionGraphicsItem *option,
                          QWidget *widget)
{
    painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
}
					

The painter's pen is 0-width by default, and its pen is initialized to the QPalette::Text brush from the paint device's palette. The brush is initialized to QPalette::Window .

Make sure to constrain all painting inside the boundaries of boundingRect () to avoid rendering artifacts (as QGraphicsView does not clip the painter for you). In particular, when QPainter renders the outline of a shape using an assigned QPen , half of the outline will be drawn outside, and half inside, the shape you're rendering (e.g., with a pen width of 2 units, you must draw outlines 1 unit inside boundingRect ()). QGraphicsItem does not support use of cosmetic pens with a non-zero width.

All painting is done in local coordinates.

注意： It is mandatory that an item will always redraw itself in the exact same way, unless update () was called; otherwise visual artifacts may occur. In other words, two subsequent calls to paint() must always produce the same output, unless update () was called between them.

注意： Enabling caching for an item does not guarantee that paint() will be invoked only once by the Graphics View framework, even without any explicit call to update (). See the documentation of setCacheMode () 了解更多细节。

另请参阅 setCacheMode (), QPen::width (), 项坐标 ，和 ItemUsesExtendedStyleOption .

QGraphicsItem *QGraphicsItem:: panel () const

返回项的面板，或 nullptr if this item does not have a panel. If the item is a panel, it will return itself. Otherwise it will return the closest ancestor that is a panel.

该函数在 Qt 4.6 引入。

另请参阅 isPanel () 和 ItemIsPanel .

QGraphicsItem::PanelModality QGraphicsItem:: panelModality () const

返回此项的模态。

该函数在 Qt 4.6 引入。

另请参阅 setPanelModality ().

QGraphicsItem *QGraphicsItem:: parentItem () const

Returns a pointer to this item's parent item. If this item does not have a parent, nullptr 被返回。

另请参阅 setParentItem () 和 childItems ().

QGraphicsObject *QGraphicsItem:: parentObject () const

Returns a pointer to the item's parent, cast to a QGraphicsObject 。返回 nullptr if the parent item is not a QGraphicsObject .

该函数在 Qt 4.6 引入。

另请参阅 parentItem () 和 childItems ().

QGraphicsWidget *QGraphicsItem:: parentWidget () const

Returns a pointer to the item's parent widget. The item's parent widget is the closest parent item that is a widget.

该函数在 Qt 4.4 引入。

另请参阅 parentItem () 和 childItems ().

QPointF QGraphicsItem:: pos () const

返回项在父级坐标中的位置。若项没有父级，其位置按场景坐标给出。

项的位置描述它在父级坐标中的原点 (本地坐标 (0, 0))；此函数的返回如同 mapToParent (0, 0).

为方便起见，也可以调用 scenePos () 以确定项在场景坐标中的位置，不管其父级。

另请参阅 x (), y (), setPos (), transform ()，和 图形视图坐标系 .

[protected] void QGraphicsItem:: prepareGeometryChange ()

为几何体改变准备项。调用此函数在改变项的边界矩形之前，以保持 QGraphicsScene 的索引更新。

prepareGeometryChange() 将调用 update () 若这是必要的。

范例：

void CircleItem::setRadius(qreal newRadius)
{
    if (radius != newRadius) {
        prepareGeometryChange();
        radius = newRadius;
    }
}
					

另请参阅 boundingRect ().

void QGraphicsItem:: removeSceneEventFilter ( QGraphicsItem * filterItem )

移除此项的事件过滤器从 filterItem .

另请参阅 installSceneEventFilter ().

void QGraphicsItem:: resetTransform ()

Resets this item's transformation matrix to the identity matrix or all the transformation properties to their default values. This is equivalent to calling setTransform(QTransform()) .

该函数在 Qt 4.3 引入。

另请参阅 setTransform () 和 transform ().

qreal QGraphicsItem:: rotation () const

Returns the clockwise rotation, in degrees, around the Z axis. The default value is 0 (i.e., the item is not rotated).

The rotation is combined with the item's scale (), transform () 和 transformations () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 setRotation (), transformOriginPoint ()，和 变换 .

qreal QGraphicsItem:: scale () const

Returns the scale factor of the item. The default scale factor is 1.0 (i.e., the item is not scaled).

The scale is combined with the item's rotation (), transform () 和 transformations () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 setScale (), rotation ()，和 变换 .

QGraphicsScene *QGraphicsItem:: scene () const

返回项的当前场景，或 nullptr 若项未存储在场景中。

要将项添加 (或移动) 到场景，调用 QGraphicsScene::addItem ().

QRectF QGraphicsItem:: sceneBoundingRect () const

Returns the bounding rect of this item in scene coordinates, by combining sceneTransform () 采用 boundingRect ().

另请参阅 boundingRect () 和 图形视图坐标系 .

[virtual protected] bool QGraphicsItem:: sceneEvent ( QEvent * event )

This virtual function receives events to this item. Reimplement this function to intercept events before they are dispatched to the specialized event handlers contextMenuEvent (), focusInEvent (), focusOutEvent (), hoverEnterEvent (), hoverMoveEvent (), hoverLeaveEvent (), keyPressEvent (), keyReleaseEvent (), mousePressEvent (), mouseReleaseEvent (), mouseMoveEvent ()，和 mouseDoubleClickEvent ().

返回 true if the event was recognized and handled; otherwise, (e.g., if the event type was not recognized,) false is returned.

event is the intercepted event.

[virtual protected] bool QGraphicsItem:: sceneEventFilter ( QGraphicsItem * watched , QEvent * event )

过滤事件为项 watched . event 是被过滤事件。

Reimplementing this function in a subclass makes it possible for the item to be used as an event filter for other items, intercepting all the events sent to those items before they are able to respond.

Reimplementations must return true to prevent further processing of a given event, ensuring that it will not be delivered to the watched item, or return false to indicate that the event should be propagated further by the event system.

另请参阅 installSceneEventFilter ().

QPointF QGraphicsItem:: scenePos () const

返回项在场景坐标中的位置。这相当于调用 mapToScene(0, 0) .

另请参阅 pos (), sceneTransform ()，和 图形视图坐标系 .

QTransform QGraphicsItem:: sceneTransform () const

返回此项的场景变换矩阵。此矩阵可以用于将坐标和几何图形形状，从此项的本地坐标系映射到场景坐标系。要从场景映射坐标，必须首先反转返回的矩阵。

范例：

QGraphicsRectItem rect;
rect.setPos(100, 100);
rect.sceneTransform().map(QPointF(0, 0));
// returns QPointF(100, 100);
rect.sceneTransform().inverted().map(QPointF(100, 100));
// returns QPointF(0, 0);
					

不像 transform ()，它只返回项的本地变换，此函数包括项的 (和任何父级的) 位置，及所有变换特性。

该函数在 Qt 4.3 引入。

另请参阅 transform (), setTransform (), scenePos (), 图形视图坐标系 ，和 变换 .

void QGraphicsItem:: scroll ( qreal dx , qreal dy , const QRectF & rect = QRectF())

卷动内容为 rect by dx , dy 。若 rect 为 null 矩形 (默认)，项的边界矩形被卷动。

卷动提供简单重新绘制的快速替代，当垂直 (或水平) 移位项内容 (或项的一部分) 时。从属当前变换和描绘设备 (即：视口) 的能力，此操作可能由使用 memmove() 将像素从一个位置移到另一位置的简单移动组成。在大多数情况下，这比重新渲染整个区域更快。

卷动后，项放出新近暴露区域的更新。若卷动不被支持 (如：正渲染到 OpenGL 视口，就不会从滚动优化中获益)，此函数相当于调用 update( rect ).

注意： 才支持滚动当 QGraphicsItem::ItemCoordinateCache 被启用；在所有其它情况下，调用此函数相当于调用 update( rect )。若确信知道项是不透明的且没有与其它项重叠，可以映射 rect 到视口坐标并卷动视口。

QTransform xform = item->deviceTransform(view->viewportTransform());
QRect deviceRect = xform.mapRect(rect).toAlignedRect();
view->viewport()->scroll(dx, dy, deviceRect);
					

该函数在 Qt 4.4 引入。

另请参阅 boundingRect ().

void QGraphicsItem:: setAcceptDrops ( bool on )

若 on 为 true，此项将接受拖放事件；否则，对于拖放事件它是透明的。默认情况下，项不接受拖放事件。

另请参阅 acceptDrops ().

void QGraphicsItem:: setAcceptHoverEvents ( bool enabled )

若 enabled is true, this item will accept hover events; otherwise, it will ignore them. By default, items do not accept hover events.

Hover events are delivered when there is no current mouse grabber item. They are sent when the mouse cursor enters an item, when it moves around inside the item, and when the cursor leaves an item. Hover events are commonly used to highlight an item when it's entered, and for tracking the mouse cursor as it hovers over the item (equivalent to QWidget::mouseTracking ).

Parent items receive hover enter events before their children, and leave events after their children. The parent does not receive a hover leave event if the cursor enters a child, though; the parent stays "hovered" until the cursor leaves its area, including its children's areas.

If a parent item handles child events, it will receive hover move, drag move, and drop events as the cursor passes through its children, but it does not receive hover enter and hover leave, nor drag enter and drag leave events on behalf of its children.

A QGraphicsWidget with window decorations will accept hover events regardless of the value of acceptHoverEvents ().

该函数在 Qt 4.4 引入。

另请参阅 acceptHoverEvents (), hoverEnterEvent (), hoverMoveEvent ()，和 hoverLeaveEvent ().

void QGraphicsItem:: setAcceptTouchEvents ( bool enabled )

若 enabled 为 True，此项将接受 触摸事件 ；否则，它会忽略它们。默认情况下，项不接受触摸事件。

该函数在 Qt 4.6 引入。

另请参阅 acceptTouchEvents ().

void QGraphicsItem:: setAcceptedMouseButtons ( Qt::MouseButtons buttons )

设置鼠标 buttons 此项接受鼠标事件。

By default, all mouse buttons are accepted. If an item accepts a mouse button, it will become the mouse grabber item when a mouse press event is delivered for that button. However, if the item does not accept the mouse button, QGraphicsScene will forward the mouse events to the first item beneath it that does.

To disable mouse events for an item (i.e., make it transparent for mouse events), call setAcceptedMouseButtons(0).

另请参阅 acceptedMouseButtons () 和 mousePressEvent ().

void QGraphicsItem:: setActive ( bool active )

若 active is true, and the scene is active, this item's panel will be activated. Otherwise, the panel is deactivated.

If the item is not part of an active scene, active will decide what happens to the panel when the scene becomes active or the item is added to the scene. If true, the item's panel will be activated when the item is either added to the scene or the scene is activated. Otherwise, the item will stay inactive independent of the scene's activated state.

该函数在 Qt 4.6 引入。

另请参阅 isPanel (), QGraphicsScene::setActivePanel ()，和 QGraphicsScene::isActive ().

void QGraphicsItem:: setBoundingRegionGranularity ( qreal granularity )

将边界区域粒度设为 granularity ; a value between and including 0 and 1. The default value is 0 (i.e., the lowest granularity, where the bounding region corresponds to the item's bounding rectangle).

The granularity is used by boundingRegion () to calculate how fine the bounding region of the item should be. The highest achievable granularity is 1, where boundingRegion () will return the finest outline possible for the respective device (e.g., for a QGraphicsView viewport, this gives you a pixel-perfect bounding region). The lowest possible granularity is 0. The value of granularity describes the ratio between device resolution and the resolution of the bounding region (e.g., a value of 0.25 will provide a region where each chunk corresponds to 4x4 device units / pixels).

该函数在 Qt 4.4 引入。

另请参阅 boundingRegionGranularity ().

void QGraphicsItem:: setCacheMode ( QGraphicsItem::CacheMode mode , const QSize & logicalCacheSize = QSize())

将项的缓存模式设为 mode .

可选 logicalCacheSize 自变量只用于 ItemCoordinateCache 模式，描述缓存缓冲的分辨率；若 logicalCacheSize 为 (100, 100)， QGraphicsItem will fit the item into 100x100 pixels in graphics memory, regardless of the logical size of the item itself. By default QGraphicsItem uses the size of boundingRect (). For all other cache modes than ItemCoordinateCache , logicalCacheSize 被忽略。

Caching can speed up rendering if your item spends a significant time redrawing itself. In some cases the cache can also slow down rendering, in particular when the item spends less time redrawing than QGraphicsItem spends redrawing from the cache.

当缓存被启用时，项的 paint () function will generally draw into an offscreen pixmap cache; for any subsequent repaint requests, the Graphics View framework will redraw from the cache. This approach works particularly well with QGLWidget, which stores all the cache as OpenGL textures.

注意， QPixmapCache 's cache limit may need to be changed to obtain optimal performance.

You can read more about the different cache modes in the CacheMode 文档编制。

注意： Enabling caching does not imply that the item's paint () function will be called only in response to an explicit update () call. For instance, under memory pressure, Qt may decide to drop some of the cache information; in such cases an item's paint () function will be called even if there was no update () call (that is, exactly as if there were no caching enabled).

该函数在 Qt 4.4 引入。

另请参阅 cacheMode (), CacheMode ，和 QPixmapCache::setCacheLimit ().

void QGraphicsItem:: setCursor (const QCursor & cursor )

Sets the current cursor shape for the item to cursor . The mouse cursor will assume this shape when it's over this item. See the 预定义光标对象列表 了解有用形状范围。

An editor item might want to use an I-beam cursor:

item->setCursor(Qt::IBeamCursor);
					

If no cursor has been set, the cursor of the item beneath is used.

另请参阅 cursor (), hasCursor (), unsetCursor (), QWidget::cursor ，和 QGuiApplication::overrideCursor ().

void QGraphicsItem:: setData ( int key , const QVariant & value )

Sets this item's custom data for the key key to value .

Custom item data is useful for storing arbitrary properties for any item. Qt does not use this feature for storing data; it is provided solely for the convenience of the user.

另请参阅 data ().

void QGraphicsItem:: setEnabled ( bool enabled )

若 enabled 为 True，项被启用；否则，被禁用。

Disabled items are visible, but they do not receive any events, and cannot take focus nor be selected. Mouse events are discarded; they are not propagated unless the item is also invisible, or if it does not accept mouse events (see acceptedMouseButtons ()). A disabled item cannot become the mouse grabber, and as a result of this, an item loses the grab if it becomes disabled when grabbing the mouse, just like it loses focus if it had focus when it was disabled.

Disabled items are traditionally drawn using grayed-out colors (see QPalette::Disabled ).

If you disable a parent item, all its children will also be disabled. If you enable a parent item, all children will be enabled, unless they have been explicitly disabled (i.e., if you call setEnabled(false) on a child, it will not be re-enabled if its parent is disabled, and then enabled again).

Items are enabled by default.

注意： If you install an event filter, you can still intercept events before they are delivered to items; this mechanism disregards the item's enabled state.

另请参阅 isEnabled ().

void QGraphicsItem:: setFiltersChildEvents ( bool enabled )

若 enabled 为 true，此项被设为过滤其所有子级的所有事件 (即：所有意图用于其任何子级的事件，取而代之都会被发送给此项)；否则，若 enabled 为 false，此项仅处理它自己的事件。默认值为 false。

该函数在 Qt 4.6 引入。

另请参阅 filtersChildEvents ().

void QGraphicsItem:: setFlag ( QGraphicsItem::GraphicsItemFlag flag , bool enabled = true)

若 enabled 为 true，项标志 flag 被启用；否则，被禁用。

另请参阅 flags () 和 setFlags ().

void QGraphicsItem:: setFlags ( QGraphicsItem::GraphicsItemFlags flags )

将项标志设为 flags 。所有标志在 flags 被启用；所有标志不在 flags 被禁用。

If the item had focus and flags does not enable ItemIsFocusable , the item loses focus as a result of calling this function. Similarly, if the item was selected, and flags does not enabled ItemIsSelectable , the item is automatically unselected.

默认情况下，不启用标志。( QGraphicsWidget 启用 ItemSendsGeometryChanges flag by default in order to track position changes.)

另请参阅 flags () 和 setFlag ().

void QGraphicsItem:: setFocus ( Qt::FocusReason focusReason = Qt::OtherFocusReason)

Gives keyboard input focus to this item. The focusReason argument will be passed into any focus event generated by this function; it is used to give an explanation of what caused the item to get focus.

Only enabled items that set the ItemIsFocusable flag can accept keyboard focus.

If this item is not visible, not active, or not associated with a scene, it will not gain immediate input focus. However, it will be registered as the preferred focus item for its subtree of items, should it later become visible.

As a result of calling this function, this item will receive a focus in event with focusReason . If another item already has focus, that item will first receive a 聚焦出事件 indicating that it has lost input focus.

另请参阅 clearFocus (), hasFocus (), focusItem ()，和 focusProxy ().

void QGraphicsItem:: setFocusProxy ( QGraphicsItem * item )

Sets the item's focus proxy to item .

If an item has a focus proxy, the focus proxy will receive input focus when the item gains input focus. The item itself will still have focus (i.e., hasFocus () will return true), but only the focus proxy will receive the keyboard input.

A focus proxy can itself have a focus proxy, and so on. In such case, keyboard input will be handled by the outermost focus proxy.

The focus proxy item must belong to the same scene as this item.

该函数在 Qt 4.6 引入。

另请参阅 focusProxy (), setFocus ()，和 hasFocus ().

void QGraphicsItem:: setGraphicsEffect ( QGraphicsEffect * effect )

设置 effect as the item's effect. If there already is an effect installed on this item, QGraphicsItem 将删除现有效果先于安装新 effect . You can delete an existing effect by calling setGraphicsEffect( nullptr ).

若 effect is the installed effect on a different item, setGraphicsEffect() will remove the effect from the item and install it on this item.

QGraphicsItem 拥有所有权对于 effect .

注意： 此函数将效果应用到自身及其所有子级。

该函数在 Qt 4.6 引入。

另请参阅 graphicsEffect ().

void QGraphicsItem:: setGroup ( QGraphicsItemGroup * group )

将此项添加到项组 group 。若 group is nullptr , this item is removed from any current group and added as a child of the previous group's parent.

另请参阅 group () 和 QGraphicsScene::createItemGroup ().

void QGraphicsItem:: setInputMethodHints ( Qt::InputMethodHints hints )

Sets the current input method hints of this item to hints .

该函数在 Qt 4.6 引入。

另请参阅 inputMethodHints () 和 inputMethodQuery ().

void QGraphicsItem:: setOpacity ( qreal opacity )

Sets this item's local opacity , between 0.0 (transparent) and 1.0 (opaque). The item's local opacity is combined with parent and ancestor opacities into the effectiveOpacity ().

By default, opacity propagates from parent to child, so if a parent's opacity is 0.5 and the child is also 0.5, the child's effective opacity will be 0.25.

The opacity property decides the state of the painter passed to the paint () function. If the item is cached, i.e., ItemCoordinateCache or DeviceCoordinateCache , the effective property will be applied to the item's cache as it is rendered.

There are two item flags that affect how the item's opacity is combined with the parent: ItemIgnoresParentOpacity and ItemDoesntPropagateOpacityToChildren .

注意： Setting the opacity of an item to 0 will not make the item invisible (according to isVisible ()), but the item will be treated like an invisible one. See the documentation of setVisible () 了解更多信息。

该函数在 Qt 4.5 引入。

另请参阅 opacity (), effectiveOpacity ()，和 setVisible ().

void QGraphicsItem:: setPanelModality ( QGraphicsItem::PanelModality panelModality )

Sets the modality for this item to panelModality .

Changing the modality of a visible item takes effect immediately.

该函数在 Qt 4.6 引入。

另请参阅 panelModality ().

void QGraphicsItem:: setParentItem ( QGraphicsItem * newParent )

Sets this item's parent item to newParent . If this item already has a parent, it is first removed from the previous parent. If newParent is 0, this item will become a top-level item.

Note that this implicitly adds this graphics item to the scene of the parent. You should not add the item to the scene yourself.

The behavior when calling this function on an item that is an ancestor of newParent is undefined.

另请参阅 parentItem () 和 childItems ().

void QGraphicsItem:: setPos (const QPointF & pos )

将项的位置设为 pos 在父级坐标。对于没有父级的项， pos 在场景坐标。

项的位置在父级坐标描述它的原点 (本地坐标 (0, 0))。

另请参阅 pos (), scenePos ()，和 图形视图坐标系 .

void QGraphicsItem:: setPos ( qreal x , qreal y )

这是重载函数。

此方便函数相当于调用 setPos( QPointF ( x , y )).

void QGraphicsItem:: setRotation ( qreal angle )

设置顺时针旋转 angle , in degrees, around the Z axis. The default value is 0 (i.e., the item is not rotated). Assigning a negative value will rotate the item counter-clockwise. Normally the rotation angle is in the range (-360, 360), but it's also possible to assign values outside of this range (e.g., a rotation of 370 degrees is the same as a rotation of 10 degrees).

The item is rotated around its transform origin point, which by default is (0, 0). You can select a different transformation origin by calling setTransformOriginPoint ().

The rotation is combined with the item's scale (), transform () 和 transformations () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 rotation (), setTransformOriginPoint ()，和 变换 .

void QGraphicsItem:: setScale ( qreal factor )

Sets the scale factor of the item. The default scale factor is 1.0 (i.e., the item is not scaled). A scale factor of 0.0 will collapse the item to a single point. If you provide a negative scale factor, the item will be flipped and mirrored (i.e., rotated 180 degrees).

The item is scaled around its transform origin point, which by default is (0, 0). You can select a different transformation origin by calling setTransformOriginPoint ().

The scale is combined with the item's rotation (), transform () 和 transformations () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 scale (), setTransformOriginPoint ()，和 变换范例 .

void QGraphicsItem:: setSelected ( bool selected )

若 selected is true and this item is selectable, this item is selected; otherwise, it is unselected.

If the item is in a group, the whole group's selected state is toggled by this function. If the group is selected, all items in the group are also selected, and if the group is not selected, no item in the group is selected.

Only visible, enabled, selectable items can be selected. If selected is true and this item is either invisible or disabled or unselectable, this function does nothing.

By default, items cannot be selected. To enable selection, set the ItemIsSelectable 标志。

This function is provided for convenience, allowing individual toggling of the selected state of an item. However, a more common way of selecting items is to call QGraphicsScene::setSelectionArea (), which will call this function for all visible, enabled, and selectable items within a specified area on the scene.

另请参阅 isSelected () 和 QGraphicsScene::selectedItems ().

void QGraphicsItem:: setToolTip (const QString & toolTip )

Sets the item's tool tip to toolTip 。若 toolTip is empty, the item's tool tip is cleared.

另请参阅 toolTip () 和 QToolTip .

void QGraphicsItem:: setTransform (const QTransform & matrix , bool combine = false)

Sets the item's current transformation matrix to matrix .

若 combine 为 true，则 matrix is combined with the current matrix; otherwise, matrix 替换 the current matrix. combine is false by default.

To simplify interaction with items using a transformed view, QGraphicsItem provides mapTo... and mapFrom... functions that can translate between items' and the scene's coordinates. For example, you can call mapToScene () to map an item coordinate to a scene coordinate, or mapFromScene () to map from scene coordinates to item coordinates.

The transformation matrix is combined with the item's rotation (), scale () 和 transformations () into a combined transformation that maps the item's coordinate system to its parent.

该函数在 Qt 4.3 引入。

另请参阅 transform (), setRotation (), setScale (), setTransformOriginPoint (), 图形视图坐标系 ，和 变换 .

void QGraphicsItem:: setTransformOriginPoint (const QPointF & origin )

设置 origin 点对于项坐标变换。

该函数在 Qt 4.6 引入。

另请参阅 transformOriginPoint () 和 变换 .

void QGraphicsItem:: setTransformOriginPoint ( qreal x , qreal y )

这是重载函数。

设置项坐标变换原点。这相当于调用 setTransformOriginPoint( QPointF ( x , y )).

该函数在 Qt 4.6 引入。

另请参阅 setTransformOriginPoint () 和 变换 .

void QGraphicsItem:: setTransformations (const QList < QGraphicsTransform *> & transformations )

Sets a list of graphics transformations ( QGraphicsTransform ) that currently apply to this item.

If all you want is to rotate or scale an item, you should call setRotation () 或 setScale () instead. If you want to set an arbitrary transformation on an item, you can call setTransform ().

QGraphicsTransform is for applying and controlling a chain of individual transformation operations on an item. It's particularly useful in animations, where each transform operation needs to be interpolated independently, or differently.

The transformations are combined with the item's rotation (), scale () 和 transform () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 transformations (), scale (), setTransformOriginPoint ()，和 变换 .

void QGraphicsItem:: setVisible ( bool visible )

若 visible 为 true, 项可见。否则，项不可见。不可见项不绘制，也不接收任何事件。尤其，鼠标事件直接穿过不可见项，并交付给可能在后面的任何项。不可见项不可选择，它们无法获得输入聚焦，且不会被检测通过 QGraphicsScene 的项定位函数。

If an item becomes invisible while grabbing the mouse, (i.e., while it is receiving mouse events,) it will automatically lose the mouse grab, and the grab is not regained by making the item visible again; it must receive a new mouse press to regain the mouse grab.

Similarly, an invisible item cannot have focus, so if the item has focus when it becomes invisible, it will lose focus, and the focus is not regained by simply making the item visible again.

If you hide a parent item, all its children will also be hidden. If you show a parent item, all children will be shown, unless they have been explicitly hidden (i.e., if you call setVisible(false) on a child, it will not be reshown even if its parent is hidden, and then shown again).

Items are visible by default; it is unnecessary to call setVisible() on a new item.

注意： An item with opacity set to 0 will still be considered visible, although it will be treated like an invisible item: mouse events will pass through it, it will not be included in the items returned by QGraphicsView::items (), and so on. However, the item will retain the focus.

另请参阅 isVisible (), show (), hide ()，和 setOpacity ().

void QGraphicsItem:: setX ( qreal x )

设置 x 坐标为项位置。相当于调用 setPos (x, y ()).

该函数在 Qt 4.6 引入。

另请参阅 x () 和 setPos ().

void QGraphicsItem:: setY ( qreal y )

设置 y 坐标为项位置。相当于调用 setPos ( x (), y).

该函数在 Qt 4.6 引入。

另请参阅 y (), x ()，和 setPos ().

void QGraphicsItem:: setZValue ( qreal z )

将项的 Z 值设为 z 。Z 值决定同级 (相邻) 项的堆叠次序。Z 值高的同级项将始终绘制在 Z 值较低的另一同级项之上。

若还原 Z 值，项的插入次序将决定其堆叠次序。

Z 值不会以任何方式影响项的大小。

默认 Z 值为 0。

另请参阅 zValue (), 排序 , stackBefore ()，和 ItemStacksBehindParent .

[虚拟] QPainterPath QGraphicsItem:: shape () const

返回此项的形状按 QPainterPath 在本地坐标。形状用于很多事情，包括碰撞检测、命中测试和对于 QGraphicsScene::items () 函数。

默认实现调用 boundingRect () to return a simple rectangular shape, but subclasses can reimplement this function to return a more accurate shape for non-rectangular items. For example, a round item may choose to return an elliptic shape for better collision detection. For example:

QPainterPath RoundItem::shape() const
{
    QPainterPath path;
    path.addEllipse(boundingRect());
    return path;
}
					

The outline of a shape can vary depending on the width and style of the pen used when drawing. If you want to include this outline in the item's shape, you can create a shape from the stroke using QPainterPathStroker .

This function is called by the default implementations of contains () 和 collidesWithPath ().

另请参阅 boundingRect (), contains (), prepareGeometryChange ()，和 QPainterPathStroker .

void QGraphicsItem:: show ()

展示项 (项默认可见)。

此方便函数相当于调用 setVisible(true) .

另请参阅 hide () 和 setVisible ().

void QGraphicsItem:: stackBefore (const QGraphicsItem * sibling )

Stacks this item before sibling , which must be a sibling item (i.e., the two items must share the same parent item, or must both be toplevel items). The sibling must have the same Z value as this item, otherwise calling this function will have no effect.

By default, all sibling items are stacked by insertion order (i.e., the first item you add is drawn before the next item you add). If two items' Z values are different, then the item with the highest Z value is drawn on top. When the Z values are the same, the insertion order will decide the stacking order.

该函数在 Qt 4.6 引入。

另请参阅 setZValue (), ItemStacksBehindParent ，和 排序 .

QGraphicsObject *QGraphicsItem:: toGraphicsObject ()

Return the graphics item cast to a QGraphicsObject , if the class is actually a graphics object, 0 otherwise.

该函数在 Qt 4.6 引入。

const QGraphicsObject *QGraphicsItem:: toGraphicsObject () const

Return the graphics item cast to a QGraphicsObject , if the class is actually a graphics object, 0 otherwise.

该函数在 Qt 4.6 引入。

QString QGraphicsItem:: toolTip () const

Returns the item's tool tip, or an empty QString if no tool tip has been set.

另请参阅 setToolTip () 和 QToolTip .

QGraphicsItem *QGraphicsItem:: topLevelItem () const

Returns this item's top-level item. The top-level item is the item's topmost ancestor item whose parent is nullptr . If an item has no parent, its own pointer is returned (i.e., a top-level item is its own top-level item).

另请参阅 parentItem ().

QGraphicsWidget *QGraphicsItem:: topLevelWidget () const

Returns a pointer to the item's top level widget (i.e., the item's ancestor whose parent is nullptr , or whose parent is not a widget), or nullptr if this item does not have a top level widget. If the item is its own top level widget, this function returns a pointer to the item itself.

该函数在 Qt 4.4 引入。

QTransform QGraphicsItem:: transform () const

返回此项的变换矩阵。

The transformation matrix is combined with the item's rotation (), scale () 和 transformations () into a combined transformations for the item.

默认变换矩阵为恒等矩阵。

该函数在 Qt 4.3 引入。

另请参阅 setTransform () 和 sceneTransform ().

QPointF QGraphicsItem:: transformOriginPoint () const

Returns the origin point for the transformation in item coordinates.

默认为 QPointF (0,0).

该函数在 Qt 4.6 引入。

另请参阅 setTransformOriginPoint () 和 变换 .

QList < QGraphicsTransform *> QGraphicsItem:: transformations () const

Returns a list of graphics transforms that currently apply to this item.

QGraphicsTransform is for applying and controlling a chain of individual transformation operations on an item. It's particularly useful in animations, where each transform operation needs to be interpolated independently, or differently.

The transformations are combined with the item's rotation (), scale () 和 transform () to map the item's coordinate system to the parent item.

该函数在 Qt 4.6 引入。

另请参阅 setTransformations (), scale (), rotation (), transformOriginPoint ()，和 变换 .

[虚拟] int QGraphicsItem:: type () const

Returns the type of an item as an int. All standard graphicsitem classes are associated with a unique value; see QGraphicsItem::Type . This type information is used by qgraphicsitem_cast () to distinguish between types.

默认实现 (在 QGraphicsItem ) returns UserType .

To enable use of qgraphicsitem_cast () with a custom item, reimplement this function and declare a Type enum value equal to your custom item's type. Custom items must return a value larger than or equal to UserType (65536).

例如：

class CustomItem : public QGraphicsItem
{
public:
   enum { Type = UserType + 1 };
   int type() const override
   {
       // Enable the use of qgraphicsitem_cast with this item.
       return Type;
   }
   ...
};
					

另请参阅 UserType .

void QGraphicsItem:: ungrabKeyboard ()

释放键盘抓取。

该函数在 Qt 4.4 引入。

另请参阅 grabKeyboard () 和 ungrabMouse ().

void QGraphicsItem:: ungrabMouse ()

释放鼠标抓取。

该函数在 Qt 4.4 引入。

另请参阅 grabMouse () 和 ungrabKeyboard ().

void QGraphicsItem:: unsetCursor ()

清零来自此项的光标。

另请参阅 hasCursor () 和 setCursor ().

void QGraphicsItem:: update (const QRectF & rect = QRectF())

调度重新绘制的区域涵盖通过 rect 在此项。可以调用此函数，每当项需要重新绘制时 (譬如：若它改变外观或大小)。

此函数不会导致立即描绘；相反，它调度的描绘请求处理通过 QGraphicsView 在控制到达事件循环之后。项才被重新绘制，若它在任何关联视图中可见。

作为项被重新描绘的副作用，其它项的重叠区域 rect 也可能被重新描绘。

若项不可见 (即 isVisible () 返回 false )，此函数什么都不做。

另请参阅 paint () 和 boundingRect ().

void QGraphicsItem:: update ( qreal x , qreal y , qreal width , qreal height )

这是重载函数。

此方便函数相当于调用 update( QRectF ( x , y , width , height )).

[protected] void QGraphicsItem:: updateMicroFocus ()

更新项的微聚焦。

该函数在 Qt 4.7 引入。

另请参阅 QInputMethod .

[virtual protected] void QGraphicsItem:: wheelEvent ( QGraphicsSceneWheelEvent * event )

此事件处理程序用于事件 event ，可以重实现以接收此项的滚轮事件。若重实现此函数， event 将默认接受。

若忽略事件，(即：通过调用 QEvent::ignore ()) 它将被传播给此项下的任何项。若没有项接受事件，它会被场景忽略，并传播给视图 (如：视图的垂直滚动条)。

默认实现忽略事件。

另请参阅 sceneEvent ().

QGraphicsWidget *QGraphicsItem:: window () const

返回项的窗口，或 nullptr 若此项没有窗口。若项是窗口，它将返回自身。否则，它将返回是窗口的最近祖先。

该函数在 Qt 4.4 引入。

另请参阅 QGraphicsWidget::isWindow ().

qreal QGraphicsItem:: x () const

此方便函数相当于调用 pos ().x().

另请参阅 setX () 和 y ().

qreal QGraphicsItem:: y () const

此方便函数相当于调用 pos ().y().

另请参阅 setY () 和 x ().

qreal QGraphicsItem:: zValue () const

返回项的 Z 值。Z 值影响同级 (相邻) 项的堆叠次序。

默认 Z 值为 0。

另请参阅 setZValue (), 排序 , stackBefore ()，和 ItemStacksBehindParent .

相关非成员

template <typename T> T qgraphicsitem_cast ( QGraphicsItem * item )

返回给定 item 被铸造成 T 类型若 item 为 T 类型；否则， nullptr 被返回。

注意： 要使此函数正确操控自定义项，重实现 type() function for each custom QGraphicsItem 子类。

该函数在 Qt 4.2 引入。

另请参阅 QGraphicsItem::type () 和 QGraphicsItem::UserType .

内容

• 公共类型

• 公共函数

• 保护函数

• 相关非成员

• 详细描述

• 变换

• 描绘

• 排序

• 事件

• 自定义数据