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# commands.cpp Example File
tools/undoframework/commands.cpp

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     ** This file is part of the example classes of the Qt Toolkit.
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     #include <QtGui>

     #include "commands.h"
     #include "diagramitem.h"

     MoveCommand::MoveCommand(DiagramItem *diagramItem, const QPointF &oldPos,
                      QUndoCommand *parent)
         : QUndoCommand(parent)
     {
         myDiagramItem = diagramItem;
         newPos = diagramItem->pos();
         myOldPos = oldPos;
     }

     bool MoveCommand::mergeWith(const QUndoCommand *command)
     {
         const MoveCommand *moveCommand = static_cast<const MoveCommand *>(command);
         DiagramItem *item = moveCommand->myDiagramItem;

         if (myDiagramItem != item)
         return false;

         newPos = item->pos();
         setText(QObject::tr("Move %1")
             .arg(createCommandString(myDiagramItem, newPos)));

         return true;
     }

     void MoveCommand::undo()
     {
         myDiagramItem->setPos(myOldPos);
         myDiagramItem->scene()->update();
         setText(QObject::tr("Move %1")
             .arg(createCommandString(myDiagramItem, newPos)));
     }

     void MoveCommand::redo()
     {
         myDiagramItem->setPos(newPos);
         setText(QObject::tr("Move %1")
             .arg(createCommandString(myDiagramItem, newPos)));
     }

     DeleteCommand::DeleteCommand(QGraphicsScene *scene, QUndoCommand *parent)
         : QUndoCommand(parent)
     {
         myGraphicsScene = scene;
         QList<QGraphicsItem *> list = myGraphicsScene->selectedItems();
         list.first()->setSelected(false);
         myDiagramItem = static_cast<DiagramItem *>(list.first());
         setText(QObject::tr("Delete %1")
             .arg(createCommandString(myDiagramItem, myDiagramItem->pos())));
     }

     void DeleteCommand::undo()
     {
         myGraphicsScene->addItem(myDiagramItem);
         myGraphicsScene->update();
     }

     void DeleteCommand::redo()
     {
         myGraphicsScene->removeItem(myDiagramItem);
     }

     AddCommand::AddCommand(DiagramItem::DiagramType addType,
                            QGraphicsScene *scene, QUndoCommand *parent)
         : QUndoCommand(parent)
     {
         static int itemCount = 0;

         myGraphicsScene = scene;
         myDiagramItem = new DiagramItem(addType);
         initialPosition = QPointF((itemCount * 15) % int(scene->width()),
                                   (itemCount * 15) % int(scene->height()));
         scene->update();
         ++itemCount;
         setText(QObject::tr("Add %1")
             .arg(createCommandString(myDiagramItem, initialPosition)));
     }

     void AddCommand::undo()
     {
         myGraphicsScene->removeItem(myDiagramItem);
         myGraphicsScene->update();
     }

     void AddCommand::redo()
     {
         myGraphicsScene->addItem(myDiagramItem);
         myDiagramItem->setPos(initialPosition);
         myGraphicsScene->clearSelection();
         myGraphicsScene->update();
     }

     QString createCommandString(DiagramItem *item, const QPointF &pos)
     {
         return QObject::tr("%1 at (%2, %3)")
             .arg(item->diagramType() == DiagramItem::Box ? "Box" : "Triangle")
             .arg(pos.x()).arg(pos.y());
     }