Qt6教程之二(4) item views

item views包括list view、tree view、table view、column view、undo view，主要用于显示数据，同时也是MVD（Model-View-Delegate，就是模型/视图/代理的意思）的view层主要显示控件。

使用model/View结构来管理数据与视图的关系，model负责数据的存取，数据的交互通过delegate来实现。这里不打算讲解MVD的原理，仅仅站在实用的角度对下列控件进行逐个演示。

list view称为列表视图，可以用来以列表的形式展示数据；

tree view称为树型视图，可以用来展示树状结构数据；

table view成为表格视图，主要用来以行列的方式展示数据；

column view成为列表控件，主要用于以列为单位展示数据的列表控件；

undo view称为撤销命令视图，用于在应用程序中实现撤消/重做功能，将撤销栈的内容显示并输出到列表控件的控件。

在前面几个章节，我们在演示代码时均通过UI布局和纯代码实现两种方式来演示控件的使用，在此将不再使用UI拖拽布局的方式，因为只有使用纯代码才能实现item views的使用！

接下来开始敲代码：

1、list view

 工程结构如下，创建的工程文件名字叫test_item_views,  窗口继承QWidget,   代码主要是在widget.cpp中写，

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include 
#include

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();


private slots:
//定义一个槽函数，用于实现鼠标点击listview项时实现逻辑
    void printMSG(QModelIndex index);


};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "qapplication.h"
#include
#include
#include
#include
#include

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    //设置窗口的位置和大小
    setGeometry(100,100,600,400);
    //创建qlistview对象
    QListView *listview=new QListView(this);
    //创建item的model对象，用于装载listview需要的数据
    QStandardItemModel *itemModel=new QStandardItemModel(this);
    
    //创建QStandardItem对象，用于管理单项数据
    QStandardItem *item=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(1)),"beijing");
    QStandardItem *item2=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(3)),"tianjing");
    QStandardItem *item3=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(5)),"guiyang");
    QStandardItem *item4=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(9)),"shenzhen");
    QStandardItem *item5=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(11)),"hainan");

    //把item装入model中
    itemModel->appendRow(item);
    itemModel->appendRow(item2);
    itemModel->appendRow(item3);
    itemModel->appendRow(item4);
    itemModel->appendRow(item5);

    //设置listview的model
    listview->setModel(itemModel);

     //连接信号与槽，实现点击单项后的逻辑   
 connect(listview,SIGNAL(clicked(QModelIndex)),this,SLOT(printMSG(QModelIndex)));


}

Widget::~Widget()
{
}



//槽函数定义：  当点击listview的单项时，把项的内容弹出来
void Widget::printMSG(QModelIndex index)
{
    QMessageBox msg;
    msg.setText ((index.data()).toString());
    msg.exec();
}

main.cpp

#include "widget.h"

#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

程序运行效果：

2、tree view

 工程结构如下，创建的工程文件名字叫test_item_views,  窗口继承QWidget,   代码主要是在widget.cpp中写，

widget.h

#ifndef WIDGET_H
#define WIDGET_H
 
#include 
#include
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
 
 
private slots:
//定义一个槽函数，用于实现鼠标点击listview项时实现逻辑
    void printMSG(QModelIndex index);
 
 
};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include
#include
#include
#include
#include
#include 
#include

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    //设置窗口的位置和大小
    setGeometry(100,100,width(),height());
    //创建treeview对象
    QTreeView *treeview=new QTreeView(this);
    treeview->setGeometry(100,100,600,600);
    treeview->setAnimated(true);

    //创建model对象，用于管理单项数据
    QFileSystemModel *fileModel=new QFileSystemModel;
    //set root path
    fileModel->setRootPath(QDir::currentPath());

    //设置listview的model
    treeview->setModel(fileModel);

     //连接信号与槽，实现点击单项后的逻辑
    connect(treeview,SIGNAL(clicked(QModelIndex)),this,SLOT(printMSG(QModelIndex)));


}

Widget::~Widget()
{
}



//槽函数定义：  当点击listview的单项时，把项的内容弹出来
void Widget::printMSG(QModelIndex index)
{
    QMessageBox msg;
    msg.setText ((index.data()).toString());
    msg.exec();
}

main.cpp

#include "widget.h"

#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

程序运行效果：

3、table view

 工程结构如下，创建的工程文件名字叫test_item_views,  窗口继承QWidget,   代码主要是在widget.cpp中写，

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include 
#include

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();


private slots:
    void printMSG(QModelIndex index);


};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "qapplication.h"
#include
#include
#include
#include
#include
#include 

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    //设置窗口的位置和大小
    setGeometry(100,100,600,400);
    //创建qlistview对象
    QTableView *tableview=new QTableView(this);

    tableview->setGeometry(100,100,600,600);

    //创建item的model对象，用于装载listview需要的数据
    QStandardItemModel *itemModel=new QStandardItemModel(this);

    //创建QStandardItem对象，用于管理单项数据
    QStandardItem *SF=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(0)),"shenfen");
    QStandardItem *item=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(1)),"beijing");
    QStandardItem *item2=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(3)),"tianjing");
    QStandardItem *item3=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(5)),"guiyang");
    QStandardItem *item4=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(9)),"shenzhen");
    QStandardItem *item5=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(11)),"hainan");

    QStandardItem *m=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(0)),"money");
    QStandardItem *item6=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(1)),"100w");
    QStandardItem *item7=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(3)),"200w");
    QStandardItem *item8=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(5)),"60w");
    QStandardItem *item9=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(9)),"300w");
    QStandardItem *item10=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(11)),"90w");


    //把item装入model中
    itemModel->setItem(0,0,SF);
    itemModel->setItem(0,1,item);
    itemModel->setItem(0,2,item2);
    itemModel->setItem(0,3,item3);
    itemModel->setItem(0,4,item4);
    itemModel->setItem(0,5,item5);

    itemModel->setItem(1,0,m);
    itemModel->setItem(1,1,item6);
    itemModel->setItem(1,2,item7);
    itemModel->setItem(1,3,item8);
    itemModel->setItem(1,4,item9);
    itemModel->setItem(1,5,item10);

    //设置listview的model
    tableview->setModel(itemModel);

     //连接信号与槽，实现点击单项后的逻辑
 connect(tableview,SIGNAL(clicked(QModelIndex)),this,SLOT(printMSG(QModelIndex)));


}

Widget::~Widget()
{
}



//槽函数定义：  当点击listview的单项时，把项的内容弹出来
void Widget::printMSG(QModelIndex index)
{
    QMessageBox msg;
    msg.setText ((index.data()).toString());
    msg.exec();
}

main.cpp

#include "widget.h"

#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

程序运行效果：

4、column view

 工程结构如下，创建的工程文件名字叫test_item_views,  窗口继承QWidget,   代码主要是在widget.cpp中写，

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include 
#include

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();


private slots:
    void printMSG(QModelIndex index);


};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "qapplication.h"
#include
#include
#include
#include
#include
#include 
#include

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    //设置窗口的位置和大小
    setGeometry(100,100,600,400);
    //创建qlistview对象
    QColumnView *columnView=new QColumnView(this);

    columnView->setGeometry(100,100,600,600);

    //创建item的model对象，用于装载listview需要的数据
    QStandardItemModel *itemModel=new QStandardItemModel(this);

    //创建QStandardItem对象，用于管理单项数据
    QStandardItem *SF=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(0)),"shenfen");
    QStandardItem *item=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(1)),"beijing");
    QStandardItem *item2=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(3)),"tianjing");
    QStandardItem *item3=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(5)),"guiyang");
    QStandardItem *item4=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(9)),"shenzhen");
    QStandardItem *item5=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(11)),"hainan");

    QStandardItem *m=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(0)),"money");
    QStandardItem *item6=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(1)),"100w");
    QStandardItem *item7=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(3)),"200w");
    QStandardItem *item8=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(5)),"60w");
    QStandardItem *item9=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(9)),"300w");
    QStandardItem *item10=new QStandardItem(QApplication::style()->standardIcon(QStyle::StandardPixmap(11)),"90w");


    //把item装入model中
    itemModel->appendRow(SF);
    itemModel->appendRow(item);
    itemModel->appendRow(item2);
    itemModel->appendRow(item3);
    itemModel->appendRow(item4);
    itemModel->appendRow(item5);

    itemModel->appendRow(m);
    itemModel->appendRow(item6);
    itemModel->appendRow(item7);
    itemModel->appendRow(item8);
    itemModel->appendRow(item9);
    itemModel->appendRow(item10);



    //设置listview的model
    columnView->setModel(itemModel);

     //连接信号与槽，实现点击单项后的逻辑
 connect(columnView,SIGNAL(clicked(QModelIndex)),this,SLOT(printMSG(QModelIndex)));


}

Widget::~Widget()
{
}



//槽函数定义：  当点击listview的单项时，把项的内容弹出来
void Widget::printMSG(QModelIndex index)
{
    QMessageBox msg;
    msg.setText ((index.data()).toString());
    msg.exec();
}

main.cpp

#include "widget.h"

#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

运行效果：

5、undo view

 undo view这个控件涉及到的知识点非常多，主要参照Qt官方示例，工程结构如下，

开始贴代码，也可以直接在Qt的官方示例中寻找，

头文件：

commands.h

#ifndef COMMANDS_H
#define COMMANDS_H

#include 
#include "document.h"

class AddShapeCommand : public QUndoCommand
{
public:
    AddShapeCommand(Document *doc, const Shape &shape,
                    QUndoCommand *parent = nullptr);
    void undo() override;
    void redo() override;

private:
    Document *m_doc;
    Shape m_shape;
    QString m_shapeName;
};

class RemoveShapeCommand : public QUndoCommand
{
public:
    RemoveShapeCommand(Document *doc, const QString &shapeName,
                       QUndoCommand *parent = nullptr);
    void undo() override;
    void redo() override;

private:
    Document *m_doc;
    Shape m_shape;
    QString m_shapeName;
};

class SetShapeColorCommand : public QUndoCommand
{
public:
    SetShapeColorCommand(Document *doc, const QString &shapeName,
                         const QColor &color, QUndoCommand *parent = nullptr);

    void undo() override;
    void redo() override;

    bool mergeWith(const QUndoCommand *command) override;
    int id() const override;

private:
    Document *m_doc;
    QString m_shapeName;
    QColor m_oldColor;
    QColor m_newColor;
};

class SetShapeRectCommand : public QUndoCommand
{
public:
    SetShapeRectCommand(Document *doc, const QString &shapeName,
                        const QRect &rect, QUndoCommand *parent = nullptr);

    void undo() override;
    void redo() override;

    bool mergeWith(const QUndoCommand *command) override;
    int id() const override;

private:
    Document *m_doc;
    QString m_shapeName;
    QRect m_oldRect;
    QRect m_newRect;
};

#endif // COMMANDS_H

document.h

#ifndef DOCUMENT_H
#define DOCUMENT_H

#include 

QT_FORWARD_DECLARE_CLASS(QUndoStack)
QT_FORWARD_DECLARE_CLASS(QTextStream)

class Shape
{
public:
    enum Type { Rectangle, Circle, Triangle };

    explicit Shape(Type type = Rectangle, const QColor &color = Qt::red, const QRect &rect = QRect());

    Type type() const;
    QString name() const;
    QRect rect() const;
    QRect resizeHandle() const;
    QColor color() const;

    static QString typeToString(Type type);
    static Type stringToType(const QString &s, bool *ok = nullptr);

    static const QSize minSize;

private:
    Type m_type;
    QRect m_rect;
    QColor m_color;
    QString m_name;

    friend class Document;
};

class Document : public QWidget
{
    Q_OBJECT

public:
    Document(QWidget *parent = nullptr);

    QString addShape(const Shape &shape);
    void deleteShape(const QString &shapeName);
    Shape shape(const QString &shapeName) const;
    QString currentShapeName() const;

    void setShapeRect(const QString &shapeName, const QRect &rect);
    void setShapeColor(const QString &shapeName, const QColor &color);

    bool load(QTextStream &stream);
    void save(QTextStream &stream);

    QString fileName() const;
    void setFileName(const QString &fileName);

    QUndoStack *undoStack() const;

signals:
    void currentShapeChanged(const QString &shapeName);

protected:
    void paintEvent(QPaintEvent *event) override;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;

private:
    void setCurrentShape(int index);
    int indexOf(const QString &shapeName) const;
    int indexAt(const QPoint &pos) const;
    QString uniqueName(const QString &name) const;

    QList m_shapeList;
    QPoint m_mousePressOffset;
    QString m_fileName;
    QUndoStack *m_undoStack = nullptr;
    int m_currentIndex = -1;
    int m_mousePressIndex = -1;
    bool m_resizeHandlePressed = false;
};

#endif // DOCUMENT_H

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include 
#include "ui_mainwindow.h"

class Document;

class MainWindow : public QMainWindow, public Ui::MainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);

    void addDocument(Document *doc);
    void removeDocument(Document *doc);
    void setCurrentDocument(Document *doc);
    Document *currentDocument() const;

public slots:
    void openDocument();
    void saveDocument();
    void closeDocument();
    void newDocument();

    void addShape();
    void removeShape();
    void setShapeColor();

    void addSnowman();
    void addRobot();

    void about();
    void aboutQt();

private slots:
    void updateActions();

private:
    QUndoGroup *m_undoGroup;

    QString fixedWindowTitle(const Document *doc) const;
};

#endif // MAINWINDOW_H

源文件：

commands.cpp

#include "commands.h"

static constexpr int setShapeRectCommandId = 1;
static constexpr int setShapeColorCommandId = 2;

/******************************************************************************
** AddShapeCommand
*/

AddShapeCommand::AddShapeCommand(Document *doc, const Shape &shape, QUndoCommand *parent)
    : QUndoCommand(parent), m_doc(doc), m_shape(shape)
{
}

void AddShapeCommand::undo()
{
    m_doc->deleteShape(m_shapeName);
}

void AddShapeCommand::redo()
{
    // A shape only gets a name when it is inserted into a document
    m_shapeName = m_doc->addShape(m_shape);
    setText(QObject::tr("Add %1").arg(m_shapeName));
}

/******************************************************************************
** RemoveShapeCommand
*/

RemoveShapeCommand::RemoveShapeCommand(Document *doc, const QString &shapeName,
                                       QUndoCommand *parent)
    : QUndoCommand(parent), m_doc(doc), m_shape(doc->shape(shapeName))
    , m_shapeName(shapeName)
{
    setText(QObject::tr("Remove %1").arg(shapeName));
}

void RemoveShapeCommand::undo()
{
    m_shapeName = m_doc->addShape(m_shape);
}

void RemoveShapeCommand::redo()
{
    m_doc->deleteShape(m_shapeName);
}

/******************************************************************************
** SetShapeColorCommand
*/

SetShapeColorCommand::SetShapeColorCommand(Document *doc, const QString &shapeName,
                                           const QColor &color, QUndoCommand *parent)
    : QUndoCommand(parent), m_doc(doc), m_shapeName(shapeName)
    , m_oldColor(doc->shape(shapeName).color()), m_newColor(color)
{
    setText(QObject::tr("Set %1's color").arg(shapeName));
}

void SetShapeColorCommand::undo()
{
    m_doc->setShapeColor(m_shapeName, m_oldColor);
}

void SetShapeColorCommand::redo()
{
    m_doc->setShapeColor(m_shapeName, m_newColor);
}

bool SetShapeColorCommand::mergeWith(const QUndoCommand *command)
{
    if (command->id() != setShapeColorCommandId)
        return false;

    const SetShapeColorCommand *other = static_cast(command);
    if (m_shapeName != other->m_shapeName)
        return false;

    m_newColor = other->m_newColor;
    return true;
}

int SetShapeColorCommand::id() const
{
    return setShapeColorCommandId;
}

/******************************************************************************
** SetShapeRectCommand
*/

SetShapeRectCommand::SetShapeRectCommand(Document *doc, const QString &shapeName,
                                         const QRect &rect, QUndoCommand *parent)
    : QUndoCommand(parent), m_doc(doc), m_shapeName(shapeName)
    , m_oldRect(doc->shape(shapeName).rect()), m_newRect(rect)
{
    setText(QObject::tr("Change %1's geometry").arg(shapeName));
}

void SetShapeRectCommand::undo()
{
    m_doc->setShapeRect(m_shapeName, m_oldRect);
}

void SetShapeRectCommand::redo()
{
    m_doc->setShapeRect(m_shapeName, m_newRect);
}

bool SetShapeRectCommand::mergeWith(const QUndoCommand *command)
{
    if (command->id() != setShapeRectCommandId)
        return false;

    const SetShapeRectCommand *other = static_cast(command);
    if (m_shapeName != other->m_shapeName)
        return false;

    m_newRect = other->m_newRect;
    return true;
}

int SetShapeRectCommand::id() const
{
    return setShapeRectCommandId;
}

mainwindow.cpp

#include "mainwindow.h"
#include "document.h"
#include "commands.h"

#include 
#include 
#include 
#include 
#include 
#include 
#include 

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setupUi(this);

    QWidget *w = documentTabs->widget(0);
    documentTabs->removeTab(0);
    delete w;

    connect(actionOpen, &QAction::triggered, this, &MainWindow::openDocument);
    connect(actionClose, &QAction::triggered, this, &MainWindow::closeDocument);
    connect(actionNew, &QAction::triggered, this, &MainWindow::newDocument);
    connect(actionSave, &QAction::triggered, this, &MainWindow::saveDocument);
    connect(actionExit, &QAction::triggered, this, &QWidget::close);
    connect(actionRed, &QAction::triggered, this, &MainWindow::setShapeColor);
    connect(actionGreen, &QAction::triggered, this, &MainWindow::setShapeColor);
    connect(actionBlue, &QAction::triggered, this, &MainWindow::setShapeColor);
    connect(actionAddCircle, &QAction::triggered, this, &MainWindow::addShape);
    connect(actionAddRectangle, &QAction::triggered, this, &MainWindow::addShape);
    connect(actionAddTriangle, &QAction::triggered, this, &MainWindow::addShape);
    connect(actionRemoveShape, &QAction::triggered, this, &MainWindow::removeShape);
    connect(actionAddRobot, &QAction::triggered, this, &MainWindow::addRobot);
    connect(actionAddSnowman, &QAction::triggered, this, &MainWindow::addSnowman);
    connect(actionAbout, &QAction::triggered, this, &MainWindow::about);
    connect(actionAboutQt, &QAction::triggered, this, &MainWindow::aboutQt);

    connect(undoLimit, &QSpinBox::valueChanged, this, &MainWindow::updateActions);
    connect(documentTabs, &QTabWidget::currentChanged, this, &MainWindow::updateActions);

    actionOpen->setShortcut(QString("Ctrl+O"));
    actionClose->setShortcut(QString("Ctrl+W"));
    actionNew->setShortcut(QString("Ctrl+N"));
    actionSave->setShortcut(QString("Ctrl+S"));
    actionExit->setShortcut(QString("Ctrl+Q"));
    actionRemoveShape->setShortcut(QString("Del"));
    actionRed->setShortcut(QString("Alt+R"));
    actionGreen->setShortcut(QString("Alt+G"));
    actionBlue->setShortcut(QString("Alt+B"));
    actionAddCircle->setShortcut(QString("Alt+C"));
    actionAddRectangle->setShortcut(QString("Alt+L"));
    actionAddTriangle->setShortcut(QString("Alt+T"));

    m_undoGroup = new QUndoGroup(this);
    undoView->setGroup(m_undoGroup);
    undoView->setCleanIcon(QIcon(":/icons/ok.png"));

    QAction *undoAction = m_undoGroup->createUndoAction(this);
    QAction *redoAction = m_undoGroup->createRedoAction(this);
    undoAction->setIcon(QIcon(":/icons/undo.png"));
    redoAction->setIcon(QIcon(":/icons/redo.png"));
    menuShape->insertAction(menuShape->actions().at(0), undoAction);
    menuShape->insertAction(undoAction, redoAction);

    toolBar->addAction(undoAction);
    toolBar->addAction(redoAction);

    newDocument();
    updateActions();
};

void MainWindow::updateActions()
{
    Document *doc = currentDocument();
    m_undoGroup->setActiveStack(doc == nullptr ? nullptr : doc->undoStack());
    QString shapeName = doc == nullptr ? QString() : doc->currentShapeName();

    actionAddRobot->setEnabled(doc != nullptr);
    actionAddSnowman->setEnabled(doc != nullptr);
    actionAddCircle->setEnabled(doc != nullptr);
    actionAddRectangle->setEnabled(doc != nullptr);
    actionAddTriangle->setEnabled(doc != nullptr);
    actionClose->setEnabled(doc != nullptr);
    actionSave->setEnabled(doc != nullptr && !doc->undoStack()->isClean());
    undoLimit->setEnabled(doc != nullptr && doc->undoStack()->count() == 0);

    if (shapeName.isEmpty()) {
        actionRed->setEnabled(false);
        actionGreen->setEnabled(false);
        actionBlue->setEnabled(false);
        actionRemoveShape->setEnabled(false);
    } else {
        Shape shape = doc->shape(shapeName);
        actionRed->setEnabled(shape.color() != Qt::red);
        actionGreen->setEnabled(shape.color() != Qt::green);
        actionBlue->setEnabled(shape.color() != Qt::blue);
        actionRemoveShape->setEnabled(true);
    }

    if (doc != nullptr) {
        int index = documentTabs->indexOf(doc);
        Q_ASSERT(index != -1);
        static const QIcon unsavedIcon(":/icons/filesave.png");
        documentTabs->setTabIcon(index, doc->undoStack()->isClean() ? QIcon() : unsavedIcon);

        if (doc->undoStack()->count() == 0)
            doc->undoStack()->setUndoLimit(undoLimit->value());
    }
}

void MainWindow::openDocument()
{
    QString fileName = QFileDialog::getOpenFileName(this);
    if (fileName.isEmpty())
        return;

    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly)) {
        QMessageBox::warning(this,
                            tr("File error"),
                            tr("Failed to open\n%1").arg(fileName));
        return;
    }
    QTextStream stream(&file);

    Document *doc = new Document();
    if (!doc->load(stream)) {
        QMessageBox::warning(this,
                            tr("Parse error"),
                            tr("Failed to parse\n%1").arg(fileName));
        delete doc;
        return;
    }

    doc->setFileName(fileName);
    addDocument(doc);
}

QString MainWindow::fixedWindowTitle(const Document *doc) const
{
    QString title = doc->fileName();

    if (title.isEmpty())
        title = tr("Unnamed");
    else
        title = QFileInfo(title).fileName();

    QString result;

    for (int i = 0; ; ++i) {
        result = title;
        if (i > 0)
            result += QString::number(i);

        bool unique = true;
        for (int j = 0; j < documentTabs->count(); ++j) {
            const QWidget *widget = documentTabs->widget(j);
            if (widget == doc)
                continue;
            if (result == documentTabs->tabText(j)) {
                unique = false;
                break;
            }
        }

        if (unique)
            break;
    }

    return result;
}

void MainWindow::addDocument(Document *doc)
{
    if (documentTabs->indexOf(doc) != -1)
        return;
    m_undoGroup->addStack(doc->undoStack());
    documentTabs->addTab(doc, fixedWindowTitle(doc));
    connect(doc, &Document::currentShapeChanged, this, &MainWindow::updateActions);
    connect(doc->undoStack(), &QUndoStack::indexChanged, this, &MainWindow::updateActions);
    connect(doc->undoStack(), &QUndoStack::cleanChanged, this, &MainWindow::updateActions);

    setCurrentDocument(doc);
}

void MainWindow::setCurrentDocument(Document *doc)
{
    documentTabs->setCurrentWidget(doc);
}

Document *MainWindow::currentDocument() const
{
    return qobject_cast(documentTabs->currentWidget());
}

void MainWindow::removeDocument(Document *doc)
{
    int index = documentTabs->indexOf(doc);
    if (index == -1)
        return;

    documentTabs->removeTab(index);
    m_undoGroup->removeStack(doc->undoStack());
    disconnect(doc, &Document::currentShapeChanged, this, &MainWindow::updateActions);
    disconnect(doc->undoStack(), &QUndoStack::indexChanged, this, &MainWindow::updateActions);
    disconnect(doc->undoStack(), &QUndoStack::cleanChanged, this, &MainWindow::updateActions);

    if (documentTabs->count() == 0) {
        newDocument();
        updateActions();
    }
}

void MainWindow::saveDocument()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    for (;;) {
        QString fileName = doc->fileName();

        if (fileName.isEmpty())
            fileName = QFileDialog::getSaveFileName(this);
        if (fileName.isEmpty())
            break;

        QFile file(fileName);
        if (!file.open(QIODevice::WriteOnly)) {
            QMessageBox::warning(this,
                                tr("File error"),
                                tr("Failed to open\n%1").arg(fileName));
            doc->setFileName(QString());
        } else {
            QTextStream stream(&file);
            doc->save(stream);
            doc->setFileName(fileName);

            int index = documentTabs->indexOf(doc);
            Q_ASSERT(index != -1);
            documentTabs->setTabText(index, fixedWindowTitle(doc));

            break;
        }
    }
}

void MainWindow::closeDocument()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    if (!doc->undoStack()->isClean()) {
        int button
            = QMessageBox::warning(this,
                            tr("Unsaved changes"),
                            tr("Would you like to save this document?"),
                            QMessageBox::Yes, QMessageBox::No);
        if (button == QMessageBox::Yes)
            saveDocument();
    }

    removeDocument(doc);
    delete doc;
}

void MainWindow::newDocument()
{
    addDocument(new Document());
}

static QColor randomColor()
{
    int r = QRandomGenerator::global()->bounded(3);
    switch (r) {
        case 0:
            return Qt::red;
        case 1:
            return Qt::green;
        default:
            break;
    }
    return Qt::blue;
}

static QRect randomRect(const QSize &s)
{
    QSize min = Shape::minSize;

    int left = qRound((s.width() - min.width()) * (QRandomGenerator::global()->bounded(1.0)));
    int top = qRound((s.height() - min.height()) * (QRandomGenerator::global()->bounded(1.0)));
    int width = qRound((s.width() - left - min.width()) * (QRandomGenerator::global()->bounded(1.0))) + min.width();
    int height = qRound((s.height() - top - min.height()) * (QRandomGenerator::global()->bounded(1.0))) + min.height();

    return QRect(left, top, width, height);
}

void MainWindow::addShape()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    Shape::Type type;

    if (sender() == actionAddCircle)
        type = Shape::Circle;
    else if (sender() == actionAddRectangle)
        type = Shape::Rectangle;
    else if (sender() == actionAddTriangle)
        type = Shape::Triangle;
    else return;

    Shape newShape(type, randomColor(), randomRect(doc->size()));
    doc->undoStack()->push(new AddShapeCommand(doc, newShape));
}

void MainWindow::removeShape()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    QString shapeName = doc->currentShapeName();
    if (shapeName.isEmpty())
        return;

    doc->undoStack()->push(new RemoveShapeCommand(doc, shapeName));
}

void MainWindow::setShapeColor()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    QString shapeName = doc->currentShapeName();
    if (shapeName.isEmpty())
        return;

    QColor color;

    if (sender() == actionRed)
        color = Qt::red;
    else if (sender() == actionGreen)
        color = Qt::green;
    else if (sender() == actionBlue)
        color = Qt::blue;
    else
        return;

    if (color == doc->shape(shapeName).color())
        return;

    doc->undoStack()->push(new SetShapeColorCommand(doc, shapeName, color));
}

void MainWindow::addSnowman()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    // Create a macro command using beginMacro() and endMacro()

    doc->undoStack()->beginMacro(tr("Add snowman"));
    doc->undoStack()->push(new AddShapeCommand(doc,
                            Shape(Shape::Circle, Qt::blue, QRect(51, 30, 97, 95))));
    doc->undoStack()->push(new AddShapeCommand(doc,
                            Shape(Shape::Circle, Qt::blue, QRect(27, 123, 150, 133))));
    doc->undoStack()->push(new AddShapeCommand(doc,
                            Shape(Shape::Circle, Qt::blue, QRect(11, 253, 188, 146))));
    doc->undoStack()->endMacro();
}

void MainWindow::addRobot()
{
    Document *doc = currentDocument();
    if (doc == nullptr)
        return;

    // Compose a macro command by explicitly adding children to a parent command

    QUndoCommand *parent = new QUndoCommand(tr("Add robot"));

    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(115, 15, 81, 70)), parent);
    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(82, 89, 148, 188)), parent);
    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(76, 280, 80, 165)), parent);
    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(163, 280, 80, 164)), parent);
    new AddShapeCommand(doc, Shape(Shape::Circle, Qt::blue, QRect(116, 25, 80, 50)), parent);
    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(232, 92, 80, 127)), parent);
    new AddShapeCommand(doc, Shape(Shape::Rectangle, Qt::green, QRect(2, 92, 80, 125)), parent);

    doc->undoStack()->push(parent);
}

void MainWindow::about()
{
    QMessageBox::about(this, tr("About Undo"), tr("The Undo demonstration shows how to use the Qt Undo framework."));
}

void MainWindow::aboutQt()
{
    QMessageBox::aboutQt(this, tr("About Qt"));
}

main.cpp

#include 
#include "mainwindow.h"

int main(int argc, char **argv)
{
    Q_INIT_RESOURCE(undo);

    QApplication app(argc, argv);

    MainWindow win;
    win.resize(800, 600);
    win.show();

    return app.exec();
}

UI布局界面：

运行效果：

undo工程文件下载资源链接：https://download.csdn.net/download/XiaoWang_csdn/87459471 

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