QUndoStack ¶

函数 ¶

槽 ¶

信号 ¶

撤消和重做动作 ¶

QUndoStack provides convenient undo and redo QAction objects, which can be inserted into a menu or a toolbar. When commands are undone or redone, QUndoStack updates the text properties of these actions to reflect what change they will trigger. The actions are also disabled when no command is available for undo or redo. These actions are returned by createUndoAction() and createRedoAction() .

命令压缩和宏 ¶

Command compression is useful when several commands can be compressed into a single command that can be undone and redone in a single operation. For example, when a user types a character in a text editor, a new command is created. This command inserts the character into the document at the cursor position. However, it is more convenient for the user to be able to undo or redo typing of whole words, sentences, or paragraphs. Command compression allows these single-character commands to be merged into a single command which inserts or deletes sections of text. For more information, see mergeWith() and push() .

A command macro is a sequence of commands, all of which are undone and redone in one go. Command macros are created by giving a command a list of child commands. Undoing or redoing the parent command will cause the child commands to be undone or redone. Command macros may be created explicitly by specifying a parent in the QUndoCommand constructor, or by using the convenience functions beginMacro() and endMacro() .

Although command compression and macros appear to have the same effect to the user, they often have different uses in an application. Commands that perform small changes to a document may be usefully compressed if there is no need to individually record them, and if only larger changes are relevant to the user. However, for commands that need to be recorded individually, or those that cannot be compressed, it is useful to use macros to provide a more convenient user experience while maintaining a record of each command.

清理状态 ¶

QUndoStack supports the concept of a clean state. When the document is saved to disk, the stack can be marked as clean using setClean() . Whenever the stack returns to this state through undoing and redoing commands, it emits the signal cleanChanged() . This signal is also emitted when the stack leaves the clean state. This signal is usually used to enable and disable the save actions in the application, and to update the document’s title to reflect that it contains unsaved changes.

过时命令 ¶

QUndoStack is able to delete commands from the stack if the command is no longer needed. One example may be to delete a command when two commands are merged together in such a way that the merged command has no function. This can be seen with move commands where the user moves their mouse to one part of the screen and then moves it to the original position. The merged command results in a mouse movement of 0. This command can be deleted since it serves no purpose. Another example is with networking commands that fail due to connection issues. In this case, the command is to be removed from the stack because the redo() and undo() functions have no function since there was connection issues.

A command can be marked obsolete with the setObsolete() function. The isObsolete() flag is checked in push() , undo() , redo() ，和 setIndex() after calling undo() , redo() and QUndoCommand :mergeWith() where applicable.

If a command is set obsolete and the clean index is greater than or equal to the current command index, then the clean index will be reset when the command is deleted from the stack.

另请参阅

QUndoCommand QUndoView

class QUndoStack ( [ parent=None ] ) ¶

param parent

QObject

Constructs an empty undo stack with the parent parent . The stack will initially be in the clean state. If parent 是 QUndoGroup object, the stack is automatically added to the group.

另请参阅

push()

PySide2.QtWidgets.QUndoStack. beginMacro ( text ) ¶

参数

text – unicode

Begins composition of a macro command with the given text description.

An empty command described by the specified text is pushed on the stack. Any subsequent commands pushed on the stack will be appended to the empty command’s children until endMacro() 被调用。

Calls to and endMacro() may be nested, but every call to must have a matching call to endMacro() .

While a macro is being composed, the stack is disabled. This means that:

• indexChanged() and cleanChanged() are not emitted,

• canUndo() and canRedo() return false,

• calling undo() or redo() has no effect,

• the undo/redo actions are disabled.

The stack becomes enabled and appropriate signals are emitted when endMacro() is called for the outermost macro.

stack.beginMacro("insert red text")
stack.push(InsertText(document, idx, text))
stack.push(SetColor(document, idx, text.length(), Qt.red))
stack.endMacro() # indexChanged() is emitted
												

This code is equivalent to:

insertRed = QUndoCommand() # an empty command
insertRed.setText("insert red text")
InsertText(document, idx, text, insertRed) # becomes child of insertRed
SetColor(document, idx, text.length(), Qt.red, insertRed)
stack.push(insertRed)
												

另请参阅

endMacro()

PySide2.QtWidgets.QUndoStack. canRedo ( ) ¶

返回类型

bool

返回 true if there is a command available for redo; otherwise returns false .

此函数返回 false if the stack is empty or if the top command on the stack has already been redone.

Synonymous with index() == count() .

另请参阅

index() canUndo()

PySide2.QtWidgets.QUndoStack. canRedoChanged ( canRedo ) ¶

参数

canRedo – bool

PySide2.QtWidgets.QUndoStack. canUndo ( ) ¶

返回类型

bool

返回 true if there is a command available for undo; otherwise returns false .

此函数返回 false if the stack is empty, or if the bottom command on the stack has already been undone.

Synonymous with index() == 0.

另请参阅

index() canRedo()

PySide2.QtWidgets.QUndoStack. canUndoChanged ( canUndo ) ¶

参数

canUndo – bool

PySide2.QtWidgets.QUndoStack. cleanChanged ( clean ) ¶

参数

clean – bool

PySide2.QtWidgets.QUndoStack. cleanIndex ( ) ¶

返回类型

int

Returns the clean index. This is the index at which setClean() was called.

A stack may not have a clean index. This happens if a document is saved, some commands are undone, then a new command is pushed. Since push() deletes all the undone commands before pushing the new command, the stack can’t return to the clean state again. In this case, this function returns -1. The -1 may also be returned after an explicit call to resetClean() .

另请参阅

isClean() setClean()

PySide2.QtWidgets.QUndoStack. clear ( ) ¶

Clears the command stack by deleting all commands on it, and returns the stack to the clean state.

Commands are not undone or redone; the state of the edited object remains unchanged.

This function is usually used when the contents of the document are abandoned.

另请参阅

QUndoStack()

PySide2.QtWidgets.QUndoStack. command ( index ) ¶

参数

index – int

返回类型

QUndoCommand

Returns a const pointer to the command at index .

This function returns a const pointer, because modifying a command, once it has been pushed onto the stack and executed, almost always causes corruption of the state of the document, if the command is later undone or redone.

另请参阅

child()

PySide2.QtWidgets.QUndoStack. count ( ) ¶

返回类型

int

Returns the number of commands on the stack. Macro commands are counted as one command.

另请参阅

index() setIndex() command()

PySide2.QtWidgets.QUndoStack. createRedoAction ( parent [ , prefix="" ] ) ¶

参数

• parent – QObject

• prefix – unicode

返回类型

QAction

Creates an redo QAction 对象采用给定 parent .

Triggering this action will cause a call to redo() . The text of this action is the text of the command which will be redone in the next call to redo() , prefixed by the specified prefix . If there is no command available for redo, this action will be disabled.

若 prefix is empty, the default template “Redo %1” is used instead of prefix. Before Qt 4.8, the prefix “Redo” was used by default.

另请参阅

createUndoAction() canRedo() text()

PySide2.QtWidgets.QUndoStack. createUndoAction ( parent [ , prefix="" ] ) ¶

参数

• parent – QObject

• prefix – unicode

返回类型

QAction

Creates an undo QAction 对象采用给定 parent .

Triggering this action will cause a call to undo() . The text of this action is the text of the command which will be undone in the next call to undo() , prefixed by the specified prefix . If there is no command available for undo, this action will be disabled.

若 prefix is empty, the default template “Undo %1” is used instead of prefix. Before Qt 4.8, the prefix “Undo” was used by default.

另请参阅

createRedoAction() canUndo() text()

PySide2.QtWidgets.QUndoStack. endMacro ( ) ¶

Ends composition of a macro command.

If this is the outermost macro in a set nested macros, this function emits indexChanged() once for the entire macro command.

另请参阅

beginMacro()

PySide2.QtWidgets.QUndoStack. index ( ) ¶

返回类型

int

Returns the index of the current command. This is the command that will be executed on the next call to redo() . It is not always the top-most command on the stack, since a number of commands may have been undone.

另请参阅

setIndex() undo() redo() count()

PySide2.QtWidgets.QUndoStack. indexChanged ( idx ) ¶

参数

idx – int

PySide2.QtWidgets.QUndoStack. isActive ( ) ¶

返回类型

bool

PySide2.QtWidgets.QUndoStack. isClean ( ) ¶

返回类型

bool

If the stack is in the clean state, returns true ；否则返回 false .

另请参阅

setClean() cleanIndex()

PySide2.QtWidgets.QUndoStack. push ( cmd ) ¶

参数

cmd – QUndoCommand

Pushes cmd on the stack or merges it with the most recently executed command. In either case, executes cmd by calling its redo() 函数。

若 cmd ‘s id is not -1, and if the id is the same as that of the most recently executed command, QUndoStack will attempt to merge the two commands by calling mergeWith() on the most recently executed command. If mergeWith() 返回 true , cmd 被删除。

After calling redo() and, if applicable, mergeWith() , isObsolete() will be called for cmd or the merged command. If isObsolete() 返回 true ，那么 cmd or the merged command will be deleted from the stack.

In all other cases cmd is simply pushed on the stack.

If commands were undone before cmd was pushed, the current command and all commands above it are deleted. Hence cmd always ends up being the top-most on the stack.

Once a command is pushed, the stack takes ownership of it. There are no getters to return the command, since modifying it after it has been executed will almost always lead to corruption of the document’s state.

另请参阅

id() mergeWith()

PySide2.QtWidgets.QUndoStack. redo ( ) ¶

Redoes the current command by calling redo() . Increments the current command index.

If the stack is empty, or if the top command on the stack has already been redone, this function does nothing.

若 isObsolete() returns true for the current command, then the command will be deleted from the stack. Additionally, if the clean index is greater than or equal to the current command index, then the clean index is reset.

另请参阅

undo() index()

PySide2.QtWidgets.QUndoStack. redoText ( ) ¶

返回类型

unicode

Returns the text of the command which will be redone in the next call to redo() .

另请参阅

actionText() undoText()

PySide2.QtWidgets.QUndoStack. redoTextChanged ( redoText ) ¶

参数

redoText – unicode

PySide2.QtWidgets.QUndoStack. resetClean ( ) ¶

Leaves the clean state and emits cleanChanged() if the stack was clean. This method resets the clean index to -1.

This is typically called in the following cases, when a document has been:

• created basing on some template and has not been saved, so no filename has been associated with the document yet.

• restored from a backup file.

• changed outside of the editor and the user did not reload it.

另请参阅

isClean() setClean() cleanIndex()

PySide2.QtWidgets.QUndoStack. setActive ( [ active=true ] ) ¶

参数

active – bool

另请参阅

isActive()

PySide2.QtWidgets.QUndoStack. setClean ( ) ¶

Marks the stack as clean and emits cleanChanged() if the stack was not already clean.

This is typically called when a document is saved, for example.

Whenever the stack returns to this state through the use of undo/redo commands, it emits the signal cleanChanged() . This signal is also emitted when the stack leaves the clean state.

另请参阅

isClean() resetClean() cleanIndex()

PySide2.QtWidgets.QUndoStack. setIndex ( idx ) ¶

参数

idx – int

Repeatedly calls undo() or redo() until the current command index reaches idx . This function can be used to roll the state of the document forwards of backwards. indexChanged() is emitted only once.

另请参阅

index() count() undo() redo()

PySide2.QtWidgets.QUndoStack. setUndoLimit ( limit ) ¶

参数

limit – int

另请参阅

undoLimit()

PySide2.QtWidgets.QUndoStack. text ( idx ) ¶

参数

idx – int

返回类型

unicode

Returns the text of the command at index idx .

另请参阅

beginMacro()

PySide2.QtWidgets.QUndoStack. undo ( ) ¶

Undoes the command below the current command by calling undo() . Decrements the current command index.

If the stack is empty, or if the bottom command on the stack has already been undone, this function does nothing.

After the command is undone, if isObsolete() 返回 true , then the command will be deleted from the stack. Additionally, if the clean index is greater than or equal to the current command index, then the clean index is reset.

另请参阅

redo() index()

PySide2.QtWidgets.QUndoStack. undoLimit ( ) ¶

返回类型

int

另请参阅

setUndoLimit()

PySide2.QtWidgets.QUndoStack. undoText ( ) ¶

返回类型

unicode

Returns the text of the command which will be undone in the next call to undo() .

另请参阅

actionText() redoText()

PySide2.QtWidgets.QUndoStack. undoTextChanged ( undoText ) ¶

参数

undoText – unicode