- Qt 6.9
- Qt GUI
- C++ Classes
- QUndoGroup
- Qt 6.9.2 Reference Documentation

# QUndoGroup Class

The QUndoGroup class is a group of QUndoStack objects. More...

Header: | `#include <QUndoGroup>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Gui)` `target_link_libraries(mytarget PRIVATE Qt6::Gui)`
qmake: | `QT += gui`
Inherits: | QObject

- List of all members, including inherited members

## Public Functions

| QUndoGroup(QObject *parent = nullptr)
virtual | ~QUndoGroup()
QUndoStack * | activeStack() const
void | addStack(QUndoStack *stack)
bool | canRedo() const
bool | canUndo() const
QAction * | createRedoAction(QObject *parent, const QString &prefix = QString()) const
QAction * | createUndoAction(QObject *parent, const QString &prefix = QString()) const
bool | isClean() const
QString | redoText() const
void | removeStack(QUndoStack *stack)
QList<QUndoStack *> | stacks() const
QString | undoText() const

## Public Slots

void | redo()
void | setActiveStack(QUndoStack *stack)
void | undo()

## Signals

void | activeStackChanged(QUndoStack *stack)
void | canRedoChanged(bool canRedo)
void | canUndoChanged(bool canUndo)
void | cleanChanged(bool clean)
void | indexChanged(int idx)
void | redoTextChanged(const QString &redoText)
void | undoTextChanged(const QString &undoText)

## Detailed Description

For an overview of the Qt's undo framework, see the overview.

An application often has multiple undo stacks, one for each opened document. At the same time, an application usually has one undo action and one redo action, which triggers undo or redo in the active document.

QUndoGroup is a group of QUndoStack objects, one of which may be active. It has an undo() and redo() slot, which calls QUndoStack::undo() and QUndoStack::redo() for the active stack. It also has the functions createUndoAction() and createRedoAction(). The actions returned by these functions behave in the same way as those returned by QUndoStack::createUndoAction() and QUndoStack::createRedoAction() of the active stack.

Stacks are added to a group with addStack() and removed with removeStack(). A stack is implicitly added to a group when it is created with the group as its parent QObject.

It is the programmer's responsibility to specify which stack is active by calling QUndoStack::setActive(), usually when the associated document window receives focus. The active stack may also be set with setActiveStack(), and is returned by activeStack().

When a stack is added to a group using addStack(), the group does not take ownership of the stack. This means the stack has to be deleted separately from the group. When a stack is deleted, it is automatically removed from a group. A stack may belong to only one group. Adding it to another group will cause it to be removed from the previous group.

A QUndoGroup is also useful in conjunction with QUndoView. If a QUndoView is set to watch a group using QUndoView::setGroup(), it will update itself to display the active stack.

## Member Function Documentation

### `[explicit]` QUndoGroup::QUndoGroup(QObject *parent = nullptr)

Creates an empty QUndoGroup object with parent parent.

See also addStack().

### `[virtual noexcept]` QUndoGroup::~QUndoGroup()

Destroys the QUndoGroup.

### QUndoStack *QUndoGroup::activeStack() const

Returns the active stack of this group.

If none of the stacks are active, or if the group is empty, this function returns `nullptr`.

See also setActiveStack() and QUndoStack::setActive().

### `[signal]` void QUndoGroup::activeStackChanged(QUndoStack *stack)

This signal is emitted whenever the active stack of the group changes. This can happen when setActiveStack() or QUndoStack::setActive() is called, or when the active stack is removed form the group. stack is the new active stack. If no stack is active, stack is 0.

See also setActiveStack() and QUndoStack::setActive().

### void QUndoGroup::addStack(QUndoStack *stack)

Adds stack to this group. The group does not take ownership of the stack. Another way of adding a stack to a group is by specifying the group as the stack's parent QObject in QUndoStack::QUndoStack(). In this case, the stack is deleted when the group is deleted, in the usual manner of QObjects.

See also removeStack(), stacks(), and QUndoStack::QUndoStack().

### bool QUndoGroup::canRedo() const

Returns the value of the active stack's QUndoStack::canRedo().

If none of the stacks are active, or if the group is empty, this function returns `false`.

See also canUndo() and setActiveStack().

### `[signal]` void QUndoGroup::canRedoChanged(bool canRedo)

This signal is emitted whenever the active stack emits QUndoStack::canRedoChanged() or the active stack changes.

canRedo is the new state, or false if the active stack is 0.

See also QUndoStack::canRedoChanged() and setActiveStack().

### bool QUndoGroup::canUndo() const

Returns the value of the active stack's QUndoStack::canUndo().

If none of the stacks are active, or if the group is empty, this function returns `false`.

See also canRedo() and setActiveStack().

### `[signal]` void QUndoGroup::canUndoChanged(bool canUndo)

This signal is emitted whenever the active stack emits QUndoStack::canUndoChanged() or the active stack changes.

canUndo is the new state, or false if the active stack is 0.

See also QUndoStack::canUndoChanged() and setActiveStack().

### `[signal]` void QUndoGroup::cleanChanged(bool clean)

This signal is emitted whenever the active stack emits QUndoStack::cleanChanged() or the active stack changes.

clean is the new state, or true if the active stack is 0.

See also QUndoStack::cleanChanged() and setActiveStack().

### QAction *QUndoGroup::createRedoAction(QObject *parent, const QString &prefix = QString()) const

Creates an redo QAction object with parent parent.

Triggering this action will cause a call to QUndoStack::redo() on the active stack. The text of this action will always be the text of the command which will be redone in the next call to redo(), prefixed by prefix. If there is no command available for redo, if the group is empty or if none of the stacks are active, this action will be disabled.

If prefix is empty, the default template "Redo %1" is used instead of prefix. Before Qt 4.8, the prefix "Redo" was used by default.

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

### QAction *QUndoGroup::createUndoAction(QObject *parent, const QString &prefix = QString()) const

Creates an undo QAction object with parent parent.

Triggering this action will cause a call to QUndoStack::undo() on the active stack. The text of this action will always be the text of the command which will be undone in the next call to undo(), prefixed by prefix. If there is no command available for undo, if the group is empty or if none of the stacks are active, this action will be disabled.

If prefix is empty, the default template "Undo %1" is used instead of prefix. Before Qt 4.8, the prefix "Undo" was used by default.

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

### `[signal]` void QUndoGroup::indexChanged(int idx)

This signal is emitted whenever the active stack emits QUndoStack::indexChanged() or the active stack changes.

idx is the new current index, or 0 if the active stack is 0.

See also QUndoStack::indexChanged() and setActiveStack().

### bool QUndoGroup::isClean() const

Returns the value of the active stack's QUndoStack::isClean().

If none of the stacks are active, or if the group is empty, this function returns `true`.

See also setActiveStack().

### `[slot]` void QUndoGroup::redo()

Calls QUndoStack::redo() on the active stack.

If none of the stacks are active, or if the group is empty, this function does nothing.

See also undo(), canRedo(), and setActiveStack().

### QString QUndoGroup::redoText() const

Returns the value of the active stack's QUndoStack::redoText().

If none of the stacks are active, or if the group is empty, this function returns an empty string.

See also undoText() and setActiveStack().

### `[signal]` void QUndoGroup::redoTextChanged(const QString &redoText)

This signal is emitted whenever the active stack emits QUndoStack::redoTextChanged() or the active stack changes.

redoText is the new state, or an empty string if the active stack is 0.

See also QUndoStack::redoTextChanged() and setActiveStack().

### void QUndoGroup::removeStack(QUndoStack *stack)

Removes stack from this group. If the stack was the active stack in the group, the active stack becomes 0.

See also addStack(), stacks(), and QUndoStack::~QUndoStack().

### `[slot]` void QUndoGroup::setActiveStack(QUndoStack *stack)

Sets the active stack of this group to stack.

If the stack is not a member of this group, this function does nothing.

Synonymous with calling QUndoStack::setActive() on stack.

The actions returned by createUndoAction() and createRedoAction() will now behave in the same way as those returned by stack's QUndoStack::createUndoAction() and QUndoStack::createRedoAction().

See also QUndoStack::setActive() and activeStack().

### QList<QUndoStack *> QUndoGroup::stacks() const

Returns a list of stacks in this group.

See also addStack() and removeStack().

### `[slot]` void QUndoGroup::undo()

Calls QUndoStack::undo() on the active stack.

If none of the stacks are active, or if the group is empty, this function does nothing.

See also redo(), canUndo(), and setActiveStack().

### QString QUndoGroup::undoText() const

Returns the value of the active stack's QUndoStack::undoText().

If none of the stacks are active, or if the group is empty, this function returns an empty string.

See also redoText() and setActiveStack().

### `[signal]` void QUndoGroup::undoTextChanged(const QString &undoText)

This signal is emitted whenever the active stack emits QUndoStack::undoTextChanged() or the active stack changes.

undoText is the new state, or an empty string if the active stack is 0.

See also QUndoStack::undoTextChanged() and setActiveStack().