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公共函数
详细描述

QUndoCommand 类

QUndoCommand class is the base class of all commands stored on a QUndoStack . 更多...

头：	#include <QUndoCommand>
qmake:	QT += widgets
Since:	Qt 4.2

所有成员列表，包括继承成员

公共函数

	QUndoCommand (QUndoCommand * parent = Q_NULLPTR)
	QUndoCommand (const QString & text , QUndoCommand * parent = Q_NULLPTR)
virtual	~QUndoCommand ()
QString	actionText () const
const QUndoCommand *	child (int index ) const
int	childCount () const
virtual int	id () const
bool	isObsolete () const
virtual bool	mergeWith (const QUndoCommand * command )
virtual void	redo ()
void	setObsolete (bool obsolete )
void	setText (const QString & text )
QString	text () const
virtual void	undo ()

详细描述

QUndoCommand class is the base class of all commands stored on a QUndoStack .

有关 Qt 撤消框架的概述，见概述文档 .

A QUndoCommand represents a single editing action on a document; for example, inserting or deleting a block of text in a text editor. QUndoCommand can apply a change to the document with redo () and undo the change with undo (). The implementations for these functions must be provided in a derived class.

class AppendText : public QUndoCommand
{
public:
    AppendText(QString *doc, const QString &text)
        : m_document(doc), m_text(text) { setText("append text"); }
    virtual void undo()
        { m_document->chop(m_text.length()); }
    virtual void redo()
        { m_document->append(m_text); }
private:
    QString *m_document;
    QString m_text;
};

A QUndoCommand has an associated text (). This is a short string describing what the command does. It is used to update the text properties of the stack's undo and redo actions; see QUndoStack::createUndoAction () 和 QUndoStack::createRedoAction ().

QUndoCommand objects are owned by the stack they were pushed on. QUndoStack deletes a command if it has been undone and a new command is pushed. For example:

MyCommand *command1 = new MyCommand();
stack->push(command1);
MyCommand *command2 = new MyCommand();
stack->push(command2);
stack->undo();
MyCommand *command3 = new MyCommand();
stack->push(command3); // command2 gets deleted

In effect, when a command is pushed, it becomes the top-most command on the stack.

To support command compression, QUndoCommand has an id () 和虚函数 mergeWith (). These functions are used by QUndoStack::push ().

To support command macros, a QUndoCommand object can have any number of child commands. Undoing or redoing the parent command will cause the child commands to be undone or redone. A command can be assigned to a parent explicitly in the constructor. In this case, the command will be owned by the parent.

The parent in this case is usually an empty command, in that it doesn't provide its own implementation of undo () 和 redo (). Instead, it uses the base implementations of these functions, which simply call undo () 或 redo () on all its children. The parent should, however, have a meaningful text ().

QUndoCommand *insertRed = new QUndoCommand(); // an empty command
insertRed->setText("insert red text");
new InsertText(document, idx, text, insertRed); // becomes child of insertRed
new SetColor(document, idx, text.length(), Qt::red, insertRed);
stack.push(insertRed);

Another way to create macros is to use the convenience functions QUndoStack::beginMacro () 和 QUndoStack::endMacro ().

另请参阅 QUndoStack .

成员函数文档编制

QUndoCommand:: QUndoCommand ( QUndoCommand * parent = Q_NULLPTR)

构造 QUndoCommand object with parent parent .

若 parent is not 0, this command is appended to parent's child list. The parent command then owns this command and will delete it in its destructor.

另请参阅 ~QUndoCommand ().

QUndoCommand:: QUndoCommand (const QString & text , QUndoCommand * parent = Q_NULLPTR)

构造 QUndoCommand 对象采用给定 parent and text .

若 parent is not 0, this command is appended to parent's child list. The parent command then owns this command and will delete it in its destructor.

另请参阅 ~QUndoCommand ().

`[virtual]` QUndoCommand:: ~QUndoCommand ()

销毁 QUndoCommand 对象和所有子级命令。

另请参阅 QUndoCommand ().

QString QUndoCommand:: actionText () const

Returns a short text string describing what this command does; for example, "insert text".

The text is used when the text properties of the stack's undo and redo actions are updated.

该函数在 Qt 4.8 引入。

另请参阅 text (), setText (), QUndoStack::createUndoAction ()，和 QUndoStack::createRedoAction ().

const QUndoCommand QUndoCommand:: child ( int index* ) const

返回子级命令在 index .

该函数在 Qt 4.4 引入。

另请参阅 childCount () 和 QUndoStack::command ().

int QUndoCommand:: childCount () const

返回此命令中的子级命令数。

该函数在 Qt 4.4 引入。

另请参阅 child ().

`[virtual]` int QUndoCommand:: id () const

返回此命令的 ID。

A command ID is used in command compression. It must be an integer unique to this command's class, or -1 if the command doesn't support compression.

If the command supports compression this function must be overridden in the derived class to return the correct ID. The base implementation returns -1.

QUndoStack::push () will only try to merge two commands if they have the same ID, and the ID is not -1.

另请参阅 mergeWith () 和 QUndoStack::push ().

bool QUndoCommand:: isObsolete () const

返回命令是否已过时。

The boolean is used for the automatic removal of commands that are not necessary in the stack anymore. The isObsolete function is checked in the functions QUndoStack::push (), QUndoStack::undo (), QUndoStack::redo ()，和 QUndoStack::setIndex ().

该函数在 Qt 5.9 引入。

另请参阅 setObsolete (), mergeWith (), QUndoStack::push (), QUndoStack::undo ()，和 QUndoStack::redo ().

`[virtual]` bool QUndoCommand:: mergeWith (const QUndoCommand * command )

试图合并此命令同 command 。返回 true 当成功时；否则返回 false .

若此函数返回 true ，调用此命令的 redo () must have the same effect as redoing both this command and command . Similarly, calling this command's undo () must have the same effect as undoing command and this command.

QUndoStack 只会试着合并 2 个命令，若它们拥有相同 ID 且 ID 不是 -1。

默认实现返回 false .

bool AppendText::mergeWith(const QUndoCommand *other)
{
    if (other->id() != id()) // make sure other is also an AppendText command
        return false;
    m_text += static_cast<const AppendText*>(other)->m_text;
    return true;
}

另请参阅 id () 和 QUndoStack::push ().

`[virtual]` void QUndoCommand:: redo ()

Applies a change to the document. This function must be implemented in the derived class. Calling QUndoStack::push (), QUndoStack::undo () 或 QUndoStack::redo () from this function leads to undefined beahavior.

默认实现在所有子级命令中调用 redo()。

另请参阅 undo ().

void QUndoCommand:: setObsolete ( bool obsolete )

将命令是否过时设为 obsolete .

该函数在 Qt 5.9 引入。

另请参阅 isObsolete (), mergeWith (), QUndoStack::push (), QUndoStack::undo ()，和 QUndoStack::redo ().

void QUndoCommand:: setText (const QString & text )

将命令文本设为 text 指定。

The specified text should be a short user-readable string describing what this command does.

If you need to have two different strings for text () 和 actionText (), separate them with "\n" and pass into this function. Even if you do not use this feature for English strings during development, you can still let translators use two different strings in order to match specific languages' needs. The described feature and the function actionText () are available since Qt 4.8.

另请参阅 text (), actionText (), QUndoStack::createUndoAction ()，和 QUndoStack::createRedoAction ().

QString QUndoCommand:: text () const

Returns a short text string describing what this command does; for example, "insert text".

The text is used for names of items in QUndoView .

另请参阅 actionText (), setText (), QUndoStack::createUndoAction ()，和 QUndoStack::createRedoAction ().

`[virtual]` void QUndoCommand:: undo ()

Reverts a change to the document. After undo() is called, the state of the document should be the same as before redo () was called. This function must be implemented in the derived class. Calling QUndoStack::push (), QUndoStack::undo () 或 QUndoStack::redo () from this function leads to undefined beahavior.

The default implementation calls undo() on all child commands in reverse order.

另请参阅 redo ().

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