The QQmlContext class defines a context within a QML engine. 更多...
| 头： | #include <QQmlContext> |
| qmake: | QT += qml |
| 继承： | QObject |
| QQmlContext (QQmlEngine * engine , QObject * parent = Q_NULLPTR) | |
| QQmlContext (QQmlContext * parentContext , QObject * parent = Q_NULLPTR) | |
| virtual | ~QQmlContext () |
| QUrl | baseUrl () const |
| QObject * | contextObject () const |
| QVariant | contextProperty (const QString & name ) const |
| QQmlEngine * | engine () const |
| bool | isValid () const |
| QString | nameForObject (QObject * object ) const |
| QQmlContext * | parentContext () const |
| QUrl | resolvedUrl (const QUrl & src ) |
| void | setBaseUrl (const QUrl & baseUrl ) |
| void | setContextObject (QObject * object ) |
| void | setContextProperty (const QString & name , QObject * value ) |
| void | setContextProperty (const QString & name , const QVariant & value ) |
The QQmlContext class defines a context within a QML engine.
Contexts allow data to be exposed to the QML components instantiated by the QML engine.
每个 QQmlContext contains a set of properties, distinct from its QObject properties, that allow data to be explicitly bound to a context by name. The context properties are defined and updated by calling QQmlContext::setContextProperty (). The following example shows a Qt model being bound to a context and then accessed from a QML file.
QQmlEngine engine; QStringListModel modelData; QQmlContext *context = new QQmlContext(engine.rootContext()); context->setContextProperty("myModel", &modelData); QQmlComponent component(&engine); component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl()); QObject *window = component.create(context);
Note it is the responsibility of the creator to delete any
QQmlContext
it constructs. If the
context
object in the example is no longer needed when the
window
component instance is destroyed, the
context
must be destroyed explicitly. The simplest way to ensure this is to set
window
as the parent of
context
.
To simplify binding and maintaining larger data sets, a context object can be set on a QQmlContext . All the properties of the context object are available by name in the context, as though they were all individually added through calls to QQmlContext::setContextProperty (). Changes to the property's values are detected through the property's notify signal. Setting a context object is both faster and easier than manually adding and maintaining context property values.
The following example has the same effect as the previous one, but it uses a context object.
class MyDataSet : ... { ... Q_PROPERTY(QAbstractItemModel *myModel READ model NOTIFY modelChanged) ... }; MyDataSet myDataSet; QQmlEngine engine; QQmlContext *context = new QQmlContext(engine.rootContext()); context->setContextObject(&myDataSet); QQmlComponent component(&engine); component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl()); component.create(context);
All properties added explicitly by QQmlContext::setContextProperty () take precedence over the context object's properties.
Contexts form a hierarchy. The root of this hierarchy is the QML engine's 根上下文 . Child contexts inherit the context properties of their parents; if a child context sets a context property that already exists in its parent, the new context property overrides that of the parent.
The following example defines two contexts -
context1
and
context2
. The second context overrides the "b" context property inherited from the first with a new value.
QQmlEngine engine; QQmlContext *context1 = new QQmlContext(engine.rootContext()); QQmlContext *context2 = new QQmlContext(context1); context1->setContextProperty("a", 12); context1->setContextProperty("b", 12); context2->setContextProperty("b", 15);
While QML objects instantiated in a context are not strictly owned by that context, their bindings are. If a context is destroyed, the property bindings of outstanding QML objects will stop evaluating.
警告： Setting the context object or adding new context properties after an object has been created in that context is an expensive operation (essentially forcing all bindings to reevaluate). Thus whenever possible you should complete "setup" of the context before using it to create any objects.
另请参阅 将 C++ 类型属性暴露给 QML .
创建新的 QQmlContext 作为子级对于 engine 's root context, and the QObject parent .
创建新的 QQmlContext 采用给定 parentContext ，和 QObject parent .
[虚拟]
QQmlContext::
~QQmlContext
()
销毁 QQmlContext .
Any expressions, or sub-contexts dependent on this context will be invalidated, but not destroyed (unless they are parented to the QQmlContext 对象)。
Returns the base url of the component, or the containing component if none is set.
另请参阅 setBaseUrl ().
Return the context object, or 0 if there is no context object.
另请参阅 setContextObject ().
返回值为 name property for this context as a QVariant .
另请参阅 setContextProperty ().
Return the context's QQmlEngine , or 0 if the context has no QQmlEngine 或 QQmlEngine was destroyed.
Returns whether the context is valid.
To be valid, a context must have a engine, and it's contextObject (), if any, must not have been deleted.
Returns the name of object in this context, or an empty string if object is not named in the context. Objects are named by setContextProperty (), or by ids in the case of QML created contexts.
If the object has multiple names, the first is returned.
Return the context's parent QQmlContext , or 0 if this context has no parent or if the parent has been destroyed.
Resolves the URL src relative to the URL of the containing component.
另请参阅 QQmlEngine::baseUrl () 和 setBaseUrl ().
Explicitly sets the url resolvedUrl () will use for relative references to baseUrl .
Calling this function will override the url of the containing component used by default.
另请参阅 baseUrl () 和 resolvedUrl ().
Set the context object .
另请参阅 contextObject ().
设置 value 的 name property on this context.
QQmlContext does not 拥有所有权对于 value .
另请参阅 contextProperty ().
Set a the value 的 name property on this context.