不废话了看代码吧:

 #include 
    
     #include 
     
      #include 
      
       #include 
       
      
     
    

class MainWindow : public QMainWindow{    Q_OBJECT

public:    explicit MainWindow(QWidget *parent = 0);    ~MainWindow()=default;

private:    void open()noexcept;    void save()noexcept;

    std::shared_ptr
    
      openAction;    std::shared_ptr
     
       saveAction;    std::shared_ptr
      
        openMenu;    std::shared_ptr
       
         theToolBar;    std::shared_ptr
        
          dockWidget;    std::shared_ptr
         
           textEdit;
         
        
       
      
     
    

protected:    virtual void closeEvent(QCloseEvent* ev)override;};

 #include "mainwindow.h"#include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
         
        
       
      
     
    

MainWindow::MainWindow(QWidget *parent) :    QMainWindow(parent){    this->setWindowTitle(tr("shihuawoaini [*]")); //注意这里的[*]这是个占位符(placeholder).

    this->setMinimumSize(500, 400);

    qDebug()<

    this->openAction = std::shared_ptr
    
     (new QAction(tr("&open"), this));    (this->openAction)->setShortcut(QKeySequence::Open); //设置快捷建.    (this->openAction)->setStatusTip(tr("open..."));    connect((this->openAction).get(), &QAction::triggered, this, &MainWindow::open);
    

    this->saveAction = std::shared_ptr
    
     (new QAction(tr("&save"), this));    saveAction->setShortcut(QKeySequence::Save); //设置快捷键.    saveAction->setStatusTip(tr("save..."));    connect(saveAction.get(), &QAction::triggered, this, &MainWindow::save);
    

    this->openMenu = std::shared_ptr
    
     (menuBar()->addMenu(tr("open")));    (this->openMenu)->addAction(this->openAction.get());
    

    this->theToolBar = std::shared_ptr
    
     (this->addToolBar(tr("File")));    (this->theToolBar)->addAction(this->openAction.get());    theToolBar->addAction(saveAction.get());
    

    this->dockWidget = std::shared_ptr
    
     (new QDockWidget(tr("DockWidget")));    this->addDockWidget(Qt::LeftDockWidgetArea, (this->dockWidget).get());
    

    this->statusTip();    this->statusBar();

    this->textEdit = std::shared_ptr
    
     (new QTextEdit(this));    this->setCentralWidget(textEdit.get());    connect(textEdit.get(), &QTextEdit::textChanged, [=](){ this->setWindowModified(true); }); //重点！！！！！！！！！！！！！！！！！！！！！ }
    

void MainWindow::open()noexcept{    QString fileName = QFileDialog::getOpenFileName(this, tr("open a file."), ".", tr("Text files(*.txt)"));

    if(!fileName.isEmpty()){        QFile file(fileName);        if(!file.open(QIODevice::ReadOnly | QIODevice::Text)){            QMessageBox::warning(this, tr("Read File"), tr("Can not open file.\n%1").arg(fileName));            return;

        }else{            QTextStream readFile(&file);            textEdit->setText(readFile.readAll());            file.close();        }

    }else{        QMessageBox::warning(this, tr("Path"), tr("You do not select any file."));    }}

void MainWindow::save()noexcept{    QString fileName = QFileDialog::getSaveFileName(this, tr("save file"),".", tr("Text files(*.txt);;Images (*.png *.jpg)"));

    if(!fileName.isEmpty()){        QFile file(fileName);

        if(!file.open(QIODevice::WriteOnly | QIODevice::Text)){            QMessageBox::warning(this, tr("write file"), tr("open nothing"));            return;        }

        QTextStream writeFile(&file);        writeFile<<(this->textEdit)->toPlainText();        file.close();

    }else{        QMessageBox::warning(this, tr("write fail"), tr("nothing for writing"));    }

}

void MainWindow::closeEvent(QCloseEvent* ev) //重点！！！！！！！！！！！！！！！！！ {    if(this->isWindowModified()){        bool boolean = QMessageBox::question(this, tr("Close Window"), tr("Do you want exit?"), QMessageBox::Yes | QMessageBox::No, QMessageBox::No) == QMessageBox::Yes;

        qDebug()<
    
     accept();        }else{            ev->ignore();        }
    

    }else{        ev->accept();    }