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diff --git a/doc/src/examples/undoframework.qdoc b/doc/src/examples/undoframework.qdoc new file mode 100644 index 0000000000..65104bd921 --- /dev/null +++ b/doc/src/examples/undoframework.qdoc @@ -0,0 +1,291 @@ +/**************************************************************************** +** +** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). +** All rights reserved. +** Contact: Nokia Corporation (qt-info@nokia.com) +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the Technology Preview License Agreement accompanying +** this package. +** +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of this +** file. +** +** If you have questions regarding the use of this file, please contact +** Nokia at qt-info@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example tools/undoframework + \title Undo Framework Example + + This example shows how to implement undo/redo functionality + with the Qt undo framework. + + \image undoframeworkexample.png The Undo Diagram Example + + In the Qt undo framework, all actions that the user performs are + implemented in classes that inherit QUndoCommand. An undo command + class knows how to both \l{QUndoCommand::}{redo()} - or just do + the first time - and \l{QUndoCommand::}{undo()} an action. For + each action the user performs, a command is placed on a + QUndoStack. Since the stack contains all commands executed + (stacked in chronological order) on the document, it can roll the + state of the document backwards and forwards by undoing and redoing + its commands. See the \l{Overview of Qt's Undo Framework}{overview + document} for a high-level introduction to the undo framework. + + The undo example implements a simple diagram application. It is + possible to add and delete items, which are either box or + rectangular shaped, and move the items by dragging them with the + mouse. The undo stack is shown in a QUndoView, which is a list in + which the commands are shown as list items. Undo and redo are + available through the edit menu. The user can also select a command + from the undo view. + + We use the \l{Graphics View Framework}{graphics view + framework} to implement the diagram. We only treat the related + code briefly as the framework has examples of its own (e.g., the + \l{Diagram Scene Example}). + + The example consists of the following classes: + + \list + \o \c MainWindow is the main window and arranges the + example's widgets. It creates the commands based + on user input and keeps them on the command stack. + \o \c AddCommand adds an item to the scene. + \o \c DeleteCommand deletes an item from the scene. + \o \c MoveCommand when an item is moved the MoveCommand keeps record + of the start and stop positions of the move, and it + moves the item according to these when \c redo() and \c undo() + is called. + \o \c DiagramScene inherits QGraphicsScene and + emits signals for the \c MoveComands when an item is moved. + \o \c DiagramItem inherits QGraphicsPolygonItem and represents + an item in the diagram. + \endlist + + \section1 MainWindow Class Definition + + \snippet examples/tools/undoframework/mainwindow.h 0 + + The \c MainWindow class maintains the undo stack, i.e., it creates + \l{QUndoCommand}s and pushes and pops them from the stack when it + receives the \c triggered() signal from \c undoAction and \c + redoAction. + + \section1 MainWindow Class Implementation + + We will start with a look at the constructor: + + \snippet examples/tools/undoframework/mainwindow.cpp 0 + + In the constructor, we set up the DiagramScene and QGraphicsView. + + Here is the \c createUndoView() function: + + \snippet examples/tools/undoframework/mainwindow.cpp 1 + + The QUndoView is a widget that display the text, which is set with + the \l{QUndoCommand::}{setText()} function, for each QUndoCommand + in the undo stack in a list. + + Here is the \c createActions() function: + + \snippet examples/tools/undoframework/mainwindow.cpp 2 + \codeline + \snippet examples/tools/undoframework/mainwindow.cpp 3 + \dots + \snippet examples/tools/undoframework/mainwindow.cpp 5 + + The \c createActions() function sets up all the examples actions + in the manner shown above. The + \l{QUndoStack::}{createUndoAction()} and + \l{QUndoStack::}{createRedoAction()} helps us crate actions that + are disabled and enabled based on the state of the stack. Also, + the text of the action will be updated automatically based on the + \l{QUndoCommand::}{text()} of the undo commands. For the other + actions we have implemented slots in the \c MainWindow class. + + Here is the \c createMenus() function: + + \snippet examples/tools/undoframework/mainwindow.cpp 6 + + \dots + \snippet examples/tools/undoframework/mainwindow.cpp 7 + \dots + \snippet examples/tools/undoframework/mainwindow.cpp 8 + + We have to use the QMenu \c aboutToShow() and \c aboutToHide() + signals since we only want \c deleteAction to be enabled when we + have selected an item. + + Here is the \c itemMoved() slot: + + \snippet examples/tools/undoframework/mainwindow.cpp 9 + + We simply push a MoveCommand on the stack, which calls \c redo() + on it. + + Here is the \c deleteItem() slot: + + \snippet examples/tools/undoframework/mainwindow.cpp 10 + + An item must be selected to be deleted. We need to check if it is + selected as the \c deleteAction may be enabled even if an item is + not selected. This can happen as we do not catch a signal or event + when an item is selected. + + Here is the \c itemMenuAboutToShow() and itemMenuAboutToHide() slots: + + \snippet examples/tools/undoframework/mainwindow.cpp 11 + \codeline + \snippet examples/tools/undoframework/mainwindow.cpp 12 + + We implement \c itemMenuAboutToShow() and \c itemMenuAboutToHide() + to get a dynamic item menu. These slots are connected to the + \l{QMenu::}{aboutToShow()} and \l{QMenu::}{aboutToHide()} signals. + We need this to disable or enable the \c deleteAction. + + Here is the \c addBox() slot: + + \snippet examples/tools/undoframework/mainwindow.cpp 13 + + The \c addBox() function creates an AddCommand and pushes it on + the undo stack. + + Here is the \c addTriangle() sot: + + \snippet examples/tools/undoframework/mainwindow.cpp 14 + + The \c addTriangle() function creates an AddCommand and pushes it + on the undo stack. + + Here is the implementation of \c about(): + + \snippet examples/tools/undoframework/mainwindow.cpp 15 + + The about slot is triggered by the \c aboutAction and displays an + about box for the example. + + \section1 AddCommand Class Definition + + \snippet examples/tools/undoframework/commands.h 2 + + The \c AddCommand class adds DiagramItem graphics items to the + DiagramScene. + + \section1 AddCommand Class Implementation + + We start with the constructor: + + \snippet examples/tools/undoframework/commands.cpp 7 + + We first create the DiagramItem to add to the DiagramScene. The + \l{QUndoCommand::}{setText()} function let us set a QString that + describes the command. We use this to get custom messages in the + QUndoView and in the menu of the main window. + + \snippet examples/tools/undoframework/commands.cpp 8 + + \c undo() removes the item from the scene. + + \snippet examples/tools/undoframework/commands.cpp 9 + + We set the position of the item as we do not do this in the + constructor. + + \section1 DeleteCommand Class Definition + + \snippet examples/tools/undoframework/commands.h 1 + + The DeleteCommand class implements the functionality to remove an + item from the scene. + + \section1 DeleteCommand Class Implementation + + \snippet examples/tools/undoframework/commands.cpp 4 + + We know that there must be one selected item as it is not possible + to create a DeleteCommand unless the item to be deleted is + selected and that only one item can be selected at any time. + The item must be unselected if it is inserted back into the + scene. + + \snippet examples/tools/undoframework/commands.cpp 5 + + The item is simply reinserted into the scene. + + \snippet examples/tools/undoframework/commands.cpp 6 + + The item is removed from the scene. + + \section1 MoveCommand Class Definition + + \snippet examples/tools/undoframework/commands.h 0 + + The \l{QUndoCommand::}{mergeWith()} is reimplemented to make + consecutive moves of an item one MoveCommand, i.e, the item will + be moved back to the start position of the first move. + + \section1 MoveCommand Class Implementation + + + The constructor of MoveCommand looks like this: + + \snippet examples/tools/undoframework/commands.cpp 0 + + We save both the old and new positions for undo and redo + respectively. + + \snippet examples/tools/undoframework/commands.cpp 2 + + We simply set the items old position and update the scene. + + \snippet examples/tools/undoframework/commands.cpp 3 + + We set the item to its new position. + + \snippet examples/tools/undoframework/commands.cpp 1 + + Whenever a MoveCommand is created, this function is called to + check if it should be merged with the previous command. It is the + previous command object that is kept on the stack. The function + returns true if the command is merged; otherwise false. + + We first check whether it is the same item that has been moved + twice, in which case we merge the commands. We update the position + of the item so that it will take the last position in the move + sequence when undone. + + \section1 DiagramScene Class Definition + + \snippet examples/tools/undoframework/diagramscene.h 0 + + The DiagramScene implements the functionality to move a + DiagramItem with the mouse. It emits a signal when a move is + completed. This is caught by the \c MainWindow, which makes + MoveCommands. We do not examine the implementation of DiagramScene + as it only deals with graphics framework issues. + + \section1 The \c main() Function + + The \c main() function of the program looks like this: + + \snippet examples/tools/undoframework/main.cpp 0 + + We draw a grid in the background of the DiagramScene, so we use a + resource file. The rest of the function creates the \c MainWindow and + shows it as a top level window. +*/ |