MainWindow.h

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include<QMainWindow>

#include<QMessageBox>

class MainWindow : public QMainWindow{

    Q_OBJECT

public:

    MainWindow();

private slots:

    void fExit();

    void iInfo();

private:

    void createMenus();

    void createActions();

    QAction *exit;

    QAction *info;

    QMenu *file;

    QMenu *about;

    QMessageBox *msgBox;

};

#endif // MAINWINDOW_H

MainWindow.cpp

#include<QtGui>

#include"MainWindow.h"

MainWindow::MainWindow(){

    QWidget *widget=new QWidget;

    setCentralWidget(widget);

    QWidget *topfiller=new QWidget;

    topfiller->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);

    QWidget *bottomFiller=new QWidget;

    bottomFiller->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);

    createActions();

    createMenus();

    QVBoxLayout *layout=new QVBoxLayout;

    layout->addWidget(topfiller);

    layout->addWidget(bottomFiller);

    widget->setLayout(layout);

    setWindowTitle(tr("Main Window"));

    resize(512,480);

}

void MainWindow::createActions(){

    exit=new QAction(tr("Exit"),this);

    exit->setShortcut(QKeySequence::Close);

    connect(exit,SIGNAL(triggered()),this,SLOT(fExit()));

    info =new QAction(tr("Info"),this);

    info->setShortcut(QKeySequence::HelpContents);

    connect(info,SIGNAL(triggered()),this,SLOT(iInfo()));

}

void MainWindow::createMenus(){

    file=menuBar()->addMenu(tr("File"));

    file->addAction(exit);

    about=menuBar()->addMenu(tr("About"));

    about->addAction(info);

}

void MainWindow::fExit(){

    MainWindow::close();

}

void MainWindow::iInfo(){

    msgBox=new QMessageBox;

    msgBox->setText(tr("hello world"));

    msgBox->setIcon(QMessageBox::Question);

    msgBox->setStandardButtons(QMessageBox::Ok);

    msgBox->exec();

}

Main.cpp

#include<QApplication>

#include"MainWindow.h"

int main(int argc,char* argv[]){

    QApplication app(argc,argv);

    MainWindow wnd;

    wnd.show();

    app.exec();

}

运行效果：