Qt QUndoCommand(实现撤回和回撤)

用到的类:

1.QUndoStack： 一个存放 QUndoCommand 命令的栈.
2.QUndoCommand：The QUndoCommand class is the base class of all commands stored on a QUndoStack.
3.QUndoView：The QUndoView class displays the contents of a QUndoStack.（显示QUndoStack的内容）

下面的例子是根据 Qt 自带的例子(undoframework)写的:

重写 QGraphicsPolygonItem (方块)

myitem.h

#ifndef MYITEM_H
#define MYITEM_H#include <QGraphicsItem>class myItem :public QGraphicsPolygonItem
{public:enum {Type = UserType +1};explicit myItem(QGraphicsItem *parent = 0);int type() const override{return Type;}
private:QPolygonF m_boxItem;
};#endif // MYITEM_H

myitem.cpp

#include "myitem.h"
#include <QBrush>
myItem::myItem(QGraphicsItem *parent)
{m_boxItem << QPointF(0,0) << QPointF(30,0)<< QPointF(30,30) << QPointF(0,30)<< QPointF(0,0);setPolygon(m_boxItem);//颜色随机QColor color( (qrand() % 256),(qrand() % 256),(qrand() % 256) );QBrush brush(color);setBrush(brush);//可移动setFlag(QGraphicsItem::ItemIsMovable);//可选中setFlag(QGraphicsItem::ItemIsSelectable);
}

重写 QGraphicsScene(场景)

myscene.h

#ifndef MYSCENE_H
#define MYSCENE_H#include <QGraphicsScene>
#include <QObject>
#include "myitem.h"
class myScene : public QGraphicsScene
{Q_OBJECT
public:myScene(QObject *parent = 0);
signals:void itemMoveSignal(myItem* item,const QPointF position);protected:void mousePressEvent(QGraphicsSceneMouseEvent *event);void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);private:QGraphicsItem * m_Item;QPointF m_oldPos;
};#endif // MYSCENE_H

myscene.cpp

#include "myscene.h"
#include <QGraphicsSceneMouseEvent>
#include <QDebug>
myScene::myScene(QObject *parent)
{m_Item = 0;}void myScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{QPointF mousePos (event->buttonDownScenePos(Qt::LeftButton).x(),event->buttonDownScenePos(Qt::LeftButton).y());const QList<QGraphicsItem* >itemList = items(mousePos);m_Item = itemList.isEmpty() ? 0 :itemList.first();if(m_Item != 0 && event->button() == Qt::LeftButton)m_oldPos = m_Item->pos();QGraphicsScene::mousePressEvent(event);}void myScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{if(m_Item != 0 && event->button() == Qt::LeftButton){if(m_oldPos != m_Item->pos())//发送位置移动的信号emit itemMoveSignal(qgraphicsitem_cast<myItem*>(m_Item),m_oldPos);m_Item = 0;}QGraphicsScene::mouseReleaseEvent(event);
}

下面重写的 QUndoCommand 才是实现撤回和回撤的模块

重写 QUndoCommand 就是重写父类的 undo() 和 redo() 方法

mycommand.h

#ifndef MYCOMMAND_H
#define MYCOMMAND_H#include <QUndoCommand>
#include "myitem.h"
#include "myscene.h"
//添加item
class addCommand :public QUndoCommand
{
public :addCommand(QGraphicsScene* graphicsScene,QUndoCommand* parent = 0);void redo() override;//重写这两个函数void undo() override;
private:myItem* m_item;QGraphicsScene* m_scene;QPointF m_initPos;
};
//移动item
class moveCommand:public QUndoCommand
{
public:moveCommand(myItem* item,const QPointF oldPos,QUndoCommand* parent = 0);void redo() override;//重写这两个函数void undo() override;
private:myItem* m_item;QPointF m_oldPos;QPointF m_newPos;};#endif // MYCOMMAND_H

mycommand.cpp

#include "mycommand.h"addCommand::addCommand(QGraphicsScene *graphicsScene, QUndoCommand *parent)
{m_scene = graphicsScene;m_item = new myItem();m_initPos = QPointF(10,10); //初始化item 生成的位置setText("add item");//undoView 中就会显示（父类的方法）
}void addCommand::redo()//stack push 时 会自动调用
{m_scene->addItem(m_item);m_item->setPos(m_initPos);m_scene->clearSelection();m_scene->update();
}void addCommand::undo()
{m_scene->removeItem(m_item);m_scene->update();
}moveCommand::moveCommand(myItem *item, const QPointF oldPos, QUndoCommand *parent)
{m_item = item;m_newPos = m_item->pos();m_oldPos = oldPos;
}void moveCommand::redo()
{m_item->setPos(m_newPos);setText(QString("Move Item:(%1,%2)").arg(m_item->pos().rx()).arg(m_item->pos().ry()));
}void moveCommand::undo()
{m_item->setPos(m_oldPos);m_item->scene()->update();setText(QString("Move Item:(%1,%2)").arg(m_item->pos().rx()).arg(m_item->pos().ry()));
}

主界面

widget.h

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QPushButton>
#include <QGraphicsView>
#include <QUndoStack>
#include <QUndoView>#include "myscene.h"
#include "myitem.h"
#include "mycommand.h"
namespace Ui {
class Widget;
}class Widget : public QWidget
{Q_OBJECTpublic:explicit Widget(QWidget *parent = 0);~Widget();void initUi();void initAction();void addItem();void itemMoved(myItem* item,QPointF pos);private:Ui::Widget *ui;QPushButton* m_addItemBtn;QAction* m_undoAction;QAction* m_redoAction;myScene *m_scene;QUndoStack* m_undoStack;QUndoView* m_undoView;
};#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QLayout>Widget::Widget(QWidget *parent) :QWidget(parent),ui(new Ui::Widget)
{ui->setupUi(this);initAction();initUi();
}Widget::~Widget()
{delete ui;
}void Widget::initUi()
{this->setWindowTitle("码农小明--撤销回撤");m_addItemBtn = new QPushButton();m_addItemBtn->setText("add Item");connect(m_addItemBtn,&QPushButton::clicked,this,&Widget::addItem);m_scene = new myScene();QBrush brush(Qt::gray);m_scene->setSceneRect(QRect(0,0,200,300));m_scene->setBackgroundBrush(brush);connect(m_scene,&myScene::itemMoveSignal,this,&Widget::itemMoved);QGraphicsView *view = new QGraphicsView(m_scene);QVBoxLayout *pLayout = new QVBoxLayout();pLayout->addWidget(m_addItemBtn);pLayout->addWidget(view);m_undoView = new QUndoView(m_undoStack);//右面显示栈内容的view(不setText就是空的)QHBoxLayout *pHLayout = new QHBoxLayout();pHLayout->addLayout(pLayout);pHLayout->addWidget(m_undoView);this->setLayout(pHLayout);this->resize(500,400);}void Widget::initAction()
{m_undoStack = new QUndoStack(this);//存放操作的栈m_undoAction = m_undoStack->createUndoAction(this,"Undo");m_undoAction->setShortcut(QKeySequence::Undo);m_redoAction = m_undoStack->createRedoAction(this,"Redo");m_redoAction->setShortcut(QKeySequence::Redo);this->addAction(m_undoAction);this->addAction(m_redoAction);
}void Widget::addItem()
{QUndoCommand* add = new addCommand(m_scene);m_undoStack->push(add);//入栈操作 会自动调用 addCommand 的 redo}void Widget::itemMoved(myItem *item, QPointF pos)
{m_undoStack->push(new moveCommand(item,pos));//入栈操作
}

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Qt QUndoCommand(实现撤回和回撤)

用到的类:

重写 QGraphicsPolygonItem (方块)

重写 QGraphicsScene(场景)

下面重写的 QUndoCommand 才是实现撤回和回撤的模块

主界面

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