commands.cpp Example File

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  #include <QtWidgets>

  #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)));
  }

  AddCommand::~AddCommand()
  {
      if (!myDiagramItem->scene())
          delete myDiagramItem;
  }

  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());
  }