mainwindow.cpp Example File

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 #include <QtWidgets>

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

 MainWindow::MainWindow()
     : mdiArea(new QMdiArea)
 {
     mdiArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
     mdiArea->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
     setCentralWidget(mdiArea);
     connect(mdiArea, &QMdiArea::subWindowActivated,
             this, &MainWindow::updateMenus);

     createActions();
     createStatusBar();
     updateMenus();

     readSettings();

     setWindowTitle(tr("MDI"));
     setUnifiedTitleAndToolBarOnMac(true);
 }

 void MainWindow::closeEvent(QCloseEvent *event)
 {
     mdiArea->closeAllSubWindows();
     if (mdiArea->currentSubWindow()) {
         event->ignore();
     } else {
         writeSettings();
         event->accept();
     }
 }

 void MainWindow::newFile()
 {
     MdiChild *child = createMdiChild();
     child->newFile();
     child->show();
 }

 void MainWindow::open()
 {
     const QString fileName = QFileDialog::getOpenFileName(this);
     if (!fileName.isEmpty())
         openFile(fileName);
 }

 bool MainWindow::openFile(const QString &fileName)
 {
     if (QMdiSubWindow *existing = findMdiChild(fileName)) {
         mdiArea->setActiveSubWindow(existing);
         return true;
     }
     const bool succeeded = loadFile(fileName);
     if (succeeded)
         statusBar()->showMessage(tr("File loaded"), 2000);
     return succeeded;
 }

 bool MainWindow::loadFile(const QString &fileName)
 {
     MdiChild *child = createMdiChild();
     const bool succeeded = child->loadFile(fileName);
     if (succeeded)
         child->show();
     else
         child->close();
     MainWindow::prependToRecentFiles(fileName);
     return succeeded;
 }

 static inline QString recentFilesKey() { return QStringLiteral("recentFileList"); }
 static inline QString fileKey() { return QStringLiteral("file"); }

 static QStringList readRecentFiles(QSettings &settings)
 {
     QStringList result;
     const int count = settings.beginReadArray(recentFilesKey());
     for (int i = 0; i < count; ++i) {
         settings.setArrayIndex(i);
         result.append(settings.value(fileKey()).toString());
     }
     settings.endArray();
     return result;
 }

 static void writeRecentFiles(const QStringList &files, QSettings &settings)
 {
     const int count = files.size();
     settings.beginWriteArray(recentFilesKey());
     for (int i = 0; i < count; ++i) {
         settings.setArrayIndex(i);
         settings.setValue(fileKey(), files.at(i));
     }
     settings.endArray();
 }

 bool MainWindow::hasRecentFiles()
 {
     QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());
     const int count = settings.beginReadArray(recentFilesKey());
     settings.endArray();
     return count > 0;
 }

 void MainWindow::prependToRecentFiles(const QString &fileName)
 {
     QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());

     const QStringList oldRecentFiles = readRecentFiles(settings);
     QStringList recentFiles = oldRecentFiles;
     recentFiles.removeAll(fileName);
     recentFiles.prepend(fileName);
     if (oldRecentFiles != recentFiles)
         writeRecentFiles(recentFiles, settings);

     setRecentFilesVisible(!recentFiles.isEmpty());
 }

 void MainWindow::setRecentFilesVisible(bool visible)
 {
     recentFileSubMenuAct->setVisible(visible);
     recentFileSeparator->setVisible(visible);
 }

 void MainWindow::updateRecentFileActions()
 {
     QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());

     const QStringList recentFiles = readRecentFiles(settings);
     const int count = qMin(int(MaxRecentFiles), recentFiles.size());
     int i = 0;
     for ( ; i < count; ++i) {
         const QString fileName = QFileInfo(recentFiles.at(i)).fileName();
         recentFileActs[i]->setText(tr("&%1 %2").arg(i + 1).arg(fileName));
         recentFileActs[i]->setData(recentFiles.at(i));
         recentFileActs[i]->setVisible(true);
     }
     for ( ; i < MaxRecentFiles; ++i)
         recentFileActs[i]->setVisible(false);
 }

 void MainWindow::openRecentFile()
 {
     if (const QAction *action = qobject_cast<const QAction *>(sender()))
         openFile(action->data().toString());
 }

 void MainWindow::save()
 {
     if (activeMdiChild() && activeMdiChild()->save())
         statusBar()->showMessage(tr("File saved"), 2000);
 }

 void MainWindow::saveAs()
 {
     MdiChild *child = activeMdiChild();
     if (child && child->saveAs()) {
         statusBar()->showMessage(tr("File saved"), 2000);
         MainWindow::prependToRecentFiles(child->currentFile());
     }
 }

 #ifndef QT_NO_CLIPBOARD
 void MainWindow::cut()
 {
     if (activeMdiChild())
         activeMdiChild()->cut();
 }

 void MainWindow::copy()
 {
     if (activeMdiChild())
         activeMdiChild()->copy();
 }

 void MainWindow::paste()
 {
     if (activeMdiChild())
         activeMdiChild()->paste();
 }
 #endif

 void MainWindow::about()
 {
    QMessageBox::about(this, tr("About MDI"),
             tr("The <b>MDI</b> example demonstrates how to write multiple "
                "document interface applications using Qt."));
 }

 void MainWindow::updateMenus()
 {
     bool hasMdiChild = (activeMdiChild() != 0);
     saveAct->setEnabled(hasMdiChild);
     saveAsAct->setEnabled(hasMdiChild);
 #ifndef QT_NO_CLIPBOARD
     pasteAct->setEnabled(hasMdiChild);
 #endif
     closeAct->setEnabled(hasMdiChild);
     closeAllAct->setEnabled(hasMdiChild);
     tileAct->setEnabled(hasMdiChild);
     cascadeAct->setEnabled(hasMdiChild);
     nextAct->setEnabled(hasMdiChild);
     previousAct->setEnabled(hasMdiChild);
     windowMenuSeparatorAct->setVisible(hasMdiChild);

 #ifndef QT_NO_CLIPBOARD
     bool hasSelection = (activeMdiChild() &&
                          activeMdiChild()->textCursor().hasSelection());
     cutAct->setEnabled(hasSelection);
     copyAct->setEnabled(hasSelection);
 #endif
 }

 void MainWindow::updateWindowMenu()
 {
     windowMenu->clear();
     windowMenu->addAction(closeAct);
     windowMenu->addAction(closeAllAct);
     windowMenu->addSeparator();
     windowMenu->addAction(tileAct);
     windowMenu->addAction(cascadeAct);
     windowMenu->addSeparator();
     windowMenu->addAction(nextAct);
     windowMenu->addAction(previousAct);
     windowMenu->addAction(windowMenuSeparatorAct);

     QList<QMdiSubWindow *> windows = mdiArea->subWindowList();
     windowMenuSeparatorAct->setVisible(!windows.isEmpty());

     for (int i = 0; i < windows.size(); ++i) {
         QMdiSubWindow *mdiSubWindow = windows.at(i);
         MdiChild *child = qobject_cast<MdiChild *>(mdiSubWindow->widget());

         QString text;
         if (i < 9) {
             text = tr("&%1 %2").arg(i + 1)
                                .arg(child->userFriendlyCurrentFile());
         } else {
             text = tr("%1 %2").arg(i + 1)
                               .arg(child->userFriendlyCurrentFile());
         }
         QAction *action = windowMenu->addAction(text, mdiSubWindow, [this, mdiSubWindow]() {
             mdiArea->setActiveSubWindow(mdiSubWindow);
         });
         action->setCheckable(true);
         action ->setChecked(child == activeMdiChild());
     }
 }

 MdiChild *MainWindow::createMdiChild()
 {
     MdiChild *child = new MdiChild;
     mdiArea->addSubWindow(child);

 #ifndef QT_NO_CLIPBOARD
     connect(child, &QTextEdit::copyAvailable, cutAct, &QAction::setEnabled);
     connect(child, &QTextEdit::copyAvailable, copyAct, &QAction::setEnabled);
 #endif

     return child;
 }

 void MainWindow::createActions()
 {
     QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
     QToolBar *fileToolBar = addToolBar(tr("File"));

     const QIcon newIcon = QIcon::fromTheme("document-new", QIcon(":/images/new.png"));
     newAct = new QAction(newIcon, tr("&New"), this);
     newAct->setShortcuts(QKeySequence::New);
     newAct->setStatusTip(tr("Create a new file"));
     connect(newAct, &QAction::triggered, this, &MainWindow::newFile);
     fileMenu->addAction(newAct);
     fileToolBar->addAction(newAct);

     const QIcon openIcon = QIcon::fromTheme("document-open", QIcon(":/images/open.png"));
     QAction *openAct = new QAction(openIcon, tr("&Open..."), this);
     openAct->setShortcuts(QKeySequence::Open);
     openAct->setStatusTip(tr("Open an existing file"));
     connect(openAct, &QAction::triggered, this, &MainWindow::open);
     fileMenu->addAction(openAct);
     fileToolBar->addAction(openAct);

     const QIcon saveIcon = QIcon::fromTheme("document-save", QIcon(":/images/save.png"));
     saveAct = new QAction(saveIcon, tr("&Save"), this);
     saveAct->setShortcuts(QKeySequence::Save);
     saveAct->setStatusTip(tr("Save the document to disk"));
     connect(saveAct, &QAction::triggered, this, &MainWindow::save);
     fileToolBar->addAction(saveAct);

     const QIcon saveAsIcon = QIcon::fromTheme("document-save-as");
     saveAsAct = new QAction(saveAsIcon, tr("Save &As..."), this);
     saveAsAct->setShortcuts(QKeySequence::SaveAs);
     saveAsAct->setStatusTip(tr("Save the document under a new name"));
     connect(saveAsAct, &QAction::triggered, this, &MainWindow::saveAs);
     fileMenu->addAction(saveAsAct);

     fileMenu->addSeparator();

     QMenu *recentMenu = fileMenu->addMenu(tr("Recent..."));
     connect(recentMenu, &QMenu::aboutToShow, this, &MainWindow::updateRecentFileActions);
     recentFileSubMenuAct = recentMenu->menuAction();

     for (int i = 0; i < MaxRecentFiles; ++i) {
         recentFileActs[i] = recentMenu->addAction(QString(), this, &MainWindow::openRecentFile);
         recentFileActs[i]->setVisible(false);
     }

     recentFileSeparator = fileMenu->addSeparator();

     setRecentFilesVisible(MainWindow::hasRecentFiles());

     fileMenu->addAction(tr("Switch layout direction"), this, &MainWindow::switchLayoutDirection);

     fileMenu->addSeparator();

     const QIcon exitIcon = QIcon::fromTheme("application-exit");
     QAction *exitAct = fileMenu->addAction(exitIcon, tr("E&xit"), qApp, &QApplication::closeAllWindows);
     exitAct->setShortcuts(QKeySequence::Quit);
     exitAct->setStatusTip(tr("Exit the application"));
     fileMenu->addAction(exitAct);

 #ifndef QT_NO_CLIPBOARD
     QMenu *editMenu = menuBar()->addMenu(tr("&Edit"));
     QToolBar *editToolBar = addToolBar(tr("Edit"));

     const QIcon cutIcon = QIcon::fromTheme("edit-cut", QIcon(":/images/cut.png"));
     cutAct = new QAction(cutIcon, tr("Cu&t"), this);
     cutAct->setShortcuts(QKeySequence::Cut);
     cutAct->setStatusTip(tr("Cut the current selection's contents to the "
                             "clipboard"));
     connect(cutAct, &QAction::triggered, this, &MainWindow::cut);
     editMenu->addAction(cutAct);
     editToolBar->addAction(cutAct);

     const QIcon copyIcon = QIcon::fromTheme("edit-copy", QIcon(":/images/copy.png"));
     copyAct = new QAction(copyIcon, tr("&Copy"), this);
     copyAct->setShortcuts(QKeySequence::Copy);
     copyAct->setStatusTip(tr("Copy the current selection's contents to the "
                              "clipboard"));
     connect(copyAct, &QAction::triggered, this, &MainWindow::copy);
     editMenu->addAction(copyAct);
     editToolBar->addAction(copyAct);

     const QIcon pasteIcon = QIcon::fromTheme("edit-paste", QIcon(":/images/paste.png"));
     pasteAct = new QAction(pasteIcon, tr("&Paste"), this);
     pasteAct->setShortcuts(QKeySequence::Paste);
     pasteAct->setStatusTip(tr("Paste the clipboard's contents into the current "
                               "selection"));
     connect(pasteAct, &QAction::triggered, this, &MainWindow::paste);
     editMenu->addAction(pasteAct);
     editToolBar->addAction(pasteAct);
 #endif

     windowMenu = menuBar()->addMenu(tr("&Window"));
     connect(windowMenu, &QMenu::aboutToShow, this, &MainWindow::updateWindowMenu);

     closeAct = new QAction(tr("Cl&ose"), this);
     closeAct->setStatusTip(tr("Close the active window"));
     connect(closeAct, &QAction::triggered,
             mdiArea, &QMdiArea::closeActiveSubWindow);

     closeAllAct = new QAction(tr("Close &All"), this);
     closeAllAct->setStatusTip(tr("Close all the windows"));
     connect(closeAllAct, &QAction::triggered, mdiArea, &QMdiArea::closeAllSubWindows);

     tileAct = new QAction(tr("&Tile"), this);
     tileAct->setStatusTip(tr("Tile the windows"));
     connect(tileAct, &QAction::triggered, mdiArea, &QMdiArea::tileSubWindows);

     cascadeAct = new QAction(tr("&Cascade"), this);
     cascadeAct->setStatusTip(tr("Cascade the windows"));
     connect(cascadeAct, &QAction::triggered, mdiArea, &QMdiArea::cascadeSubWindows);

     nextAct = new QAction(tr("Ne&xt"), this);
     nextAct->setShortcuts(QKeySequence::NextChild);
     nextAct->setStatusTip(tr("Move the focus to the next window"));
     connect(nextAct, &QAction::triggered, mdiArea, &QMdiArea::activateNextSubWindow);

     previousAct = new QAction(tr("Pre&vious"), this);
     previousAct->setShortcuts(QKeySequence::PreviousChild);
     previousAct->setStatusTip(tr("Move the focus to the previous "
                                  "window"));
     connect(previousAct, &QAction::triggered, mdiArea, &QMdiArea::activatePreviousSubWindow);

     windowMenuSeparatorAct = new QAction(this);
     windowMenuSeparatorAct->setSeparator(true);

     updateWindowMenu();

     menuBar()->addSeparator();

     QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));

     QAction *aboutAct = helpMenu->addAction(tr("&About"), this, &MainWindow::about);
     aboutAct->setStatusTip(tr("Show the application's About box"));

     QAction *aboutQtAct = helpMenu->addAction(tr("About &Qt"), qApp, &QApplication::aboutQt);
     aboutQtAct->setStatusTip(tr("Show the Qt library's About box"));
 }

 void MainWindow::createStatusBar()
 {
     statusBar()->showMessage(tr("Ready"));
 }

 void MainWindow::readSettings()
 {
     QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());
     const QByteArray geometry = settings.value("geometry", QByteArray()).toByteArray();
     if (geometry.isEmpty()) {
         const QRect availableGeometry = QApplication::desktop()->availableGeometry(this);
         resize(availableGeometry.width() / 3, availableGeometry.height() / 2);
         move((availableGeometry.width() - width()) / 2,
              (availableGeometry.height() - height()) / 2);
     } else {
         restoreGeometry(geometry);
     }
 }

 void MainWindow::writeSettings()
 {
     QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());
     settings.setValue("geometry", saveGeometry());
 }

 MdiChild *MainWindow::activeMdiChild() const
 {
     if (QMdiSubWindow *activeSubWindow = mdiArea->activeSubWindow())
         return qobject_cast<MdiChild *>(activeSubWindow->widget());
     return 0;
 }

 QMdiSubWindow *MainWindow::findMdiChild(const QString &fileName) const
 {
     QString canonicalFilePath = QFileInfo(fileName).canonicalFilePath();

     foreach (QMdiSubWindow *window, mdiArea->subWindowList()) {
         MdiChild *mdiChild = qobject_cast<MdiChild *>(window->widget());
         if (mdiChild->currentFile() == canonicalFilePath)
             return window;
     }
     return 0;
 }

 void MainWindow::switchLayoutDirection()
 {
     if (layoutDirection() == Qt::LeftToRight)
         QGuiApplication::setLayoutDirection(Qt::RightToLeft);
     else
         QGuiApplication::setLayoutDirection(Qt::LeftToRight);
 }