com.trolltech.qt.gui
Class QUndoStack

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QObject
                  extended by com.trolltech.qt.gui.QUndoStack
All Implemented Interfaces:
QtJambiInterface

public class QUndoStack
extends QObject

The QUndoStack class is a stack of QUndoCommand objects. For an overview of Qt's Undo Framework, see the overview document.

An undo stack maintains a stack of commands that have been applied to a document.

New commands are pushed on the stack using push(). Commands can be undone and redone using undo() and redo(), or by triggering the actions returned by createUndoAction() and createRedoAction().

QUndoStack keeps track of the current command. This is the command which will be executed by the next call to redo(). The index of this command is returned by index(). The state of the edited object can be rolled forward or back using setIndex(). If the top-most command on the stack has already been redone, index() is equal to count().

QUndoStack provides support for undo and redo actions, command compression, command macros, and supports the concept of a clean state.

Undo and Redo Actions

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 QUndoStack::createUndoAction() and QUndoStack::createRedoAction().

Command Compression and Macros

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
QUndoCommand::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.

Clean State

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.

See also:
QUndoCommand, and QUndoView.


Nested Class Summary
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 QSignalEmitter.Signal1 canRedoChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 canUndoChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 cleanChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 indexChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 redoTextChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 undoTextChanged
          This signal takes 1 generic argument(s).
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QUndoStack()
          Constructs an empty undo stack with the parent parent.
QUndoStack(QObject parent)
          Constructs an empty undo stack with the parent parent.
 
Method Summary
 void beginMacro(java.lang.String text)
          Begins composition of a macro command with the given text description.
 boolean canRedo()
          Returns true if there is a command available for redo; otherwise returns false.
 boolean canUndo()
          Returns true if there is a command available for undo; otherwise returns false.
 int cleanIndex()
          Returns the clean index.
 void clear()
          Clears the command stack by deleting all commands on it, and returns the stack to the clean state.
 QUndoCommand command(int index)
          Returns a const pointer to the command at index.
 int count()
          Returns the number of commands on the stack.
 QAction createRedoAction(QObject parent)
          Creates an redo QAction object with the given parent.
 QAction createRedoAction(QObject parent, java.lang.String prefix)
          Creates an redo QAction object with the given parent.
 QAction createUndoAction(QObject parent)
          Creates an undo QAction object with the given parent.
 QAction createUndoAction(QObject parent, java.lang.String prefix)
          Creates an undo QAction object with the given parent.
 void endMacro()
          Ends composition of a macro command.
 int index()
          Returns the index of the current command.
 boolean isActive()
          This property holds the active status of this stack.
 boolean isClean()
          If the stack is in the clean state, returns true; otherwise returns false.
 void push(QUndoCommand cmd)
          Pushes cmd on the stack or merges it with the most recently executed command.
 void redo()
          Redoes the current command by calling QUndoCommand::redo().
 java.lang.String redoText()
          Returns the text of the command which will be redone in the next call to redo().
 void setActive()
          This property holds the active status of this stack.
 void setActive(boolean active)
          This property holds the active status of this stack.
 void setClean()
          Marks the stack as clean and emits cleanChanged() if the stack was not already clean.
 void setIndex(int idx)
          Repeatedly calls undo() or redo() until the the current command index reaches idx.
 void setUndoLimit(int limit)
          This property holds the maximum number of commands on this stack.
 java.lang.String text(int idx)
          Returns the text of the command at index idx.
 void undo()
          Undoes the command below the current command by calling QUndoCommand::undo().
 int undoLimit()
          This property holds the maximum number of commands on this stack.
 java.lang.String undoText()
          Returns the text of the command which will be undone in the next call to undo().
 
Methods inherited from class com.trolltech.qt.core.QObject
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Field Detail

canRedoChanged

public final QSignalEmitter.Signal1 canRedoChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.Boolean(named: canRedo)>:

This signal is emitted whenever the value of canRedo() changes. It is used to enable or disable the redo action returned by createRedoAction(). canRedo specifies the new value.


canUndoChanged

public final QSignalEmitter.Signal1 canUndoChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.Boolean(named: canUndo)>:

This signal is emitted whenever the value of canUndo() changes. It is used to enable or disable the undo action returned by createUndoAction(). canUndo specifies the new value.


cleanChanged

public final QSignalEmitter.Signal1 cleanChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.Boolean(named: clean)>:

This signal is emitted whenever the stack enters or leaves the clean state. If clean is true, the stack is in a clean state; otherwise this signal indicates that it has left the clean state.

See also:
isClean(), and setClean().


indexChanged

public final QSignalEmitter.Signal1 indexChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.Integer(named: idx)>:

This signal is emitted whenever a command modifies the state of the document. This happens when a command is undone or redone. When a macro command is undone or redone, or setIndex() is called, this signal is emitted only once.

idx specifies the index of the current command, ie. the command which will be executed on the next call to redo().

See also:
index(), and setIndex().


redoTextChanged

public final QSignalEmitter.Signal1 redoTextChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.String(named: redoText)>:

This signal is emitted whenever the value of redoText() changes. It is used to update the text property of the redo action returned by createRedoAction(). redoText specifies the new text.


undoTextChanged

public final QSignalEmitter.Signal1 undoTextChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.String(named: undoText)>:

This signal is emitted whenever the value of undoText() changes. It is used to update the text property of the undo action returned by createUndoAction(). undoText specifies the new text.

Constructor Detail

QUndoStack

public QUndoStack()
Constructs an empty undo stack with the parent parent. The stack will initally be in the clean state. If parent is a QUndoGroup object, the stack is automatically added to the group.

See also:
push().


QUndoStack

public QUndoStack(QObject parent)
Constructs an empty undo stack with the parent parent. The stack will initally be in the clean state. If parent is a QUndoGroup object, the stack is automatically added to the group.

See also:
push().

Method Detail

beginMacro

public final void beginMacro(java.lang.String text)
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() is called.

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

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

The stack becomes enabled and appropriate signals are emitted when endMacro() is called for the outermost macro.
        stack.beginMacro("insert red text");
        stack.push(new InsertText(document, idx, text));
        stack.push(new SetColor(document, idx, text.length(), Qt.GlobalColor.red));
        stack.endMacro(); // indexChanged() is emitted
This code is equivalent to:
        QUndoCommand nsertRed = 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.GlobalColor.red, insertRed);

        stack.push(insertRed);

See also:
endMacro().


canRedo

public final boolean canRedo()
Returns true if there is a command available for redo; otherwise returns false.

This function returns false if the stack is empty or if the top command on the stack has already been redone.

Synonymous with index() == count().

See also:
index(), and canUndo().


canUndo

public final boolean canUndo()
Returns true if there is a command available for undo; otherwise returns false.

This function returns false if the stack is empty, or if the bottom command on the stack has already been undone.

Synonymous with index() == 0.

See also:
index(), and canRedo().


cleanIndex

public final int cleanIndex()
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.

See also:
isClean(), and setClean().


clear

public final void 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.

See also:
QUndoStack().


command

public final QUndoCommand command(int index)
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.

See also:
QUndoCommand::child().


count

public final int count()
Returns the number of commands on the stack. Macro commands are counted as one command.

See also:
index(), setIndex(), and command().


createRedoAction

public final QAction createRedoAction(QObject parent)
Creates an redo QAction object with the given 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.

If prefix is empty, the default prefix "Redo" is used.

See also:
createUndoAction(), canRedo(), and QUndoCommand::text().


createRedoAction

public final QAction createRedoAction(QObject parent,
                                      java.lang.String prefix)
Creates an redo QAction object with the given 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.

If prefix is empty, the default prefix "Redo" is used.

See also:
createUndoAction(), canRedo(), and QUndoCommand::text().


createUndoAction

public final QAction createUndoAction(QObject parent)
Creates an undo QAction object with the given 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.

If prefix is empty, the default prefix "Undo" is used.

See also:
createRedoAction(), canUndo(), and QUndoCommand::text().


createUndoAction

public final QAction createUndoAction(QObject parent,
                                      java.lang.String prefix)
Creates an undo QAction object with the given 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.

If prefix is empty, the default prefix "Undo" is used.

See also:
createRedoAction(), canUndo(), and QUndoCommand::text().


endMacro

public final void 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.

See also:
beginMacro().


index

public final int index()
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.

See also:
setIndex(), undo(), redo(), and count().


isActive

public final boolean isActive()
This property holds the active status of this stack. An application often has multiple undo stacks, one for each opened document. The active stack is the one associated with the currently active document. If the stack belongs to a QUndoGroup, calls to QUndoGroup::undo() or QUndoGroup::redo() will be forwarded to this stack when it is active. If the QUndoGroup is watched by a QUndoView, the view will display the contents of this stack when it is active. If the stack does not belong to a QUndoGroup, making it active has no effect.

It is the programmer's responsibility to specify which stack is active by calling setActive(), usually when the associated document window receives focus.

See also:
QUndoGroup.


isClean

public final boolean isClean()
If the stack is in the clean state, returns true; otherwise returns false.

See also:
setClean(), and cleanIndex().


push

public final void push(QUndoCommand cmd)
Pushes cmd on the stack or merges it with the most recently executed command. In either case, executes cmd by calling its redo() function.

If 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 QUndoCommand::mergeWith() on the most recently executed command. If QUndoCommand::mergeWith() returns true, cmd is deleted.

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.

See also:
QUndoCommand::id(), and QUndoCommand::mergeWith().


redo

public final void redo()
Redoes the current command by calling QUndoCommand::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.

See also:
undo(), and index().


redoText

public final java.lang.String redoText()
Returns the text of the command which will be redone in the next call to redo().

See also:
QUndoCommand::text(), and undoText().


setActive

public final void setActive()
This property holds the active status of this stack. An application often has multiple undo stacks, one for each opened document. The active stack is the one associated with the currently active document. If the stack belongs to a QUndoGroup, calls to QUndoGroup::undo() or QUndoGroup::redo() will be forwarded to this stack when it is active. If the QUndoGroup is watched by a QUndoView, the view will display the contents of this stack when it is active. If the stack does not belong to a QUndoGroup, making it active has no effect.

It is the programmer's responsibility to specify which stack is active by calling setActive(), usually when the associated document window receives focus.

See also:
QUndoGroup.


setActive

public final void setActive(boolean active)
This property holds the active status of this stack. An application often has multiple undo stacks, one for each opened document. The active stack is the one associated with the currently active document. If the stack belongs to a QUndoGroup, calls to QUndoGroup::undo() or QUndoGroup::redo() will be forwarded to this stack when it is active. If the QUndoGroup is watched by a QUndoView, the view will display the contents of this stack when it is active. If the stack does not belong to a QUndoGroup, making it active has no effect.

It is the programmer's responsibility to specify which stack is active by calling setActive(), usually when the associated document window receives focus.

See also:
QUndoGroup.


setClean

public final void setClean()
Marks the stack as clean and emits cleanChanged() if the stack was not already clean.

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.

See also:
isClean(), and cleanIndex().


setIndex

public final void setIndex(int idx)
Repeatedly calls undo() or redo() until the 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.

See also:
index(), count(), undo(), and redo().


setUndoLimit

public final void setUndoLimit(int limit)
This property holds the maximum number of commands on this stack. When the number of commands on a stack exceedes the stack's undoLimit, commands are deleted from the bottom of the stack. Macro commands (commands with child commands) are treated as one command. The default value is 0, which means that there is no limit.

This property may only be set when the undo stack is empty, since setting it on a non-empty stack might delete the command at the current index. Calling setUndoLimit() on a non-empty stack prints a warning and does nothing.


text

public final java.lang.String text(int idx)
Returns the text of the command at index idx.

See also:
beginMacro().


undo

public final void undo()
Undoes the command below the current command by calling QUndoCommand::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.

See also:
redo(), and index().


undoLimit

public final int undoLimit()
This property holds the maximum number of commands on this stack. When the number of commands on a stack exceedes the stack's undoLimit, commands are deleted from the bottom of the stack. Macro commands (commands with child commands) are treated as one command. The default value is 0, which means that there is no limit.

This property may only be set when the undo stack is empty, since setting it on a non-empty stack might delete the command at the current index. Calling setUndoLimit() on a non-empty stack prints a warning and does nothing.


undoText

public final java.lang.String undoText()
Returns the text of the command which will be undone in the next call to undo().

See also:
QUndoCommand::text(), and redoText().