QUndoStack class is a stack of QUndoCommand 对象。 更多...
| 头： | #include <QUndoStack> |
| qmake: | QT += widgets |
| Since: | Qt 4.2 |
| 继承： | QObject |
| QUndoStack (QObject * parent = Q_NULLPTR) | |
| ~QUndoStack () | |
| void | beginMacro (const QString & text ) |
| bool | canRedo () const |
| bool | canUndo () const |
| int | cleanIndex () const |
| void | clear () |
| const QUndoCommand * | command (int index ) const |
| int | count () const |
| QAction * | createRedoAction (QObject * parent , const QString & prefix = QString()) const |
| QAction * | createUndoAction (QObject * parent , const QString & prefix = QString()) const |
| void | endMacro () |
| int | index () const |
| bool | isActive () const |
| bool | isClean () const |
| void | push (QUndoCommand * cmd ) |
| QString | redoText () const |
| void | setUndoLimit (int limit ) |
| QString | text (int idx ) const |
| int | undoLimit () const |
| QString | undoText () const |
| void | redo () |
| void | resetClean () |
| void | setActive (bool active = true) |
| void | setClean () |
| void | setIndex (int idx ) |
| void | undo () |
| 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 ) |
QUndoStack class is a stack of QUndoCommand 对象。
有关 Qt 撤消框架的概述，见 概述文档 .
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 () 和 redo (), or by triggering the actions returned by createUndoAction () 和 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 .
QUndoStack 提供方便撤消和重做 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 () 和 QUndoStack::createRedoAction ().
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 () 和 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 () 和 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.
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.
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 () 和 undo () functions have no function since there was connection issues.
A command can be marked obsolete with the QUndoCommand::setObsolete () 函数。 QUndoCommand::isObsolete () flag is checked in QUndoStack::push (), QUndoStack::undo (), QUndoStack::redo ()，和 QUndoStack::setIndex () after calling QUndoCommand::undo (), QUndoCommand::redo () 和 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 and QUndoView .
此特性保持此堆栈的活动状态。
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 () 或 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.
访问函数：
| bool | isActive () const |
| void | setActive (bool active = true) |
另请参阅 QUndoGroup .
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.
该特性在 Qt 4.3 引入。
访问函数：
| int | undoLimit () const |
| void | setUndoLimit (int limit ) |
构造空撤消堆栈采用父级 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 ().
Destroys the undo stack, deleting any commands that are on it. If the stack is in a QUndoGroup , the stack is automatically removed from the group.
另请参阅 QUndoStack ().
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 beginMacro() and endMacro () may be nested, but every call to beginMacro() must have a matching call to endMacro ().
While a macro is being 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::red)); stack.endMacro(); // indexChanged() is emitted
此代码相当于：
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);
另请参阅 endMacro ().
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 ().
[signal]
void
QUndoStack::
canRedoChanged
(
bool
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.
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.
[signal]
void
QUndoStack::
canUndoChanged
(
bool
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.
[signal]
void
QUndoStack::
cleanChanged
(
bool
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.
另请参阅 isClean () 和 setClean ().
Returns the clean index. This is the index at which setClean () 被调用。
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 () 和 setClean ().
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 ().
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.
该函数在 Qt 4.4 引入。
另请参阅 QUndoCommand::child ().
Returns the number of commands on the stack. Macro commands are counted as one command.
另请参阅 index (), setIndex ()，和 command ().
创建重做 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 ()，和 QUndoCommand::text ().
创建撤消 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 ()，和 QUndoCommand::text ().
结束宏命令的合成。
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 ().
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 ()，和 count ().
[signal]
void
QUndoStack::
indexChanged
(
int
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 ().
若堆栈处于清理状态，返回
true
；否则返回
false
.
另请参阅 setClean () 和 cleanIndex ().
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
QUndoCommand::mergeWith
() on the most recently executed command. If
QUndoCommand::mergeWith
() 返回
true
,
cmd
被删除。
After calling
QUndoCommand::redo
() and, if applicable,
QUndoCommand::mergeWith
(),
QUndoCommand::isObsolete
() will be called for
cmd
or the merged command. If
QUndoCommand::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 QUndoCommand::id () 和 QUndoCommand::mergeWith ().
[slot]
void
QUndoStack::
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.
若 QUndoCommand::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.
Returns the text of the command which will be redone in the next call to redo ().
另请参阅 QUndoCommand::actionText () 和 undoText ().
[signal]
void
QUndoStack::
redoTextChanged
(const
QString
&
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.
[slot]
void
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:
该函数在 Qt 5.8 引入。
另请参阅 isClean (), setClean ()，和 cleanIndex ().
[slot]
void
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 ()，和 cleanIndex ().
[slot]
void
QUndoStack::
setIndex
(
int
idx
)
Repeatedly calls undo () 或 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 ()，和 redo ().
Returns the text of the command at index idx .
另请参阅 beginMacro ().
[slot]
void
QUndoStack::
undo
()
Undoes the command below the current command by calling QUndoCommand::undo ()。递减当前命令索引。
If the stack is empty, or if the bottom command on the stack has already been undone, this function does nothing.
在撤消命令后，若
QUndoCommand::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.
Returns the text of the command which will be undone in the next call to undo ().
另请参阅 QUndoCommand::actionText () 和 redoText ().
[signal]
void
QUndoStack::
undoTextChanged
(const
QString
&
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.