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mainwindow.cpp Example File
mainwindows/mdi/mainwindow.cpp

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 #include <QtGui>

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

 MainWindow::MainWindow()
 {
     mdiArea = new QMdiArea;
     setCentralWidget(mdiArea);
     connect(mdiArea, SIGNAL(subWindowActivated(QMdiSubWindow *)),
             this, SLOT(updateMenus()));
     windowMapper = new QSignalMapper(this);
     connect(windowMapper, SIGNAL(mapped(QWidget *)),
             this, SLOT(setActiveSubWindow(QWidget *)));

     createActions();
     createMenus();
     createToolBars();
     createStatusBar();
     updateMenus();

     readSettings();

     setWindowTitle(tr("MDI"));
 }

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

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

 void MainWindow::open()
 {
     QString fileName = QFileDialog::getOpenFileName(this);
     if (!fileName.isEmpty()) {
         QMdiSubWindow *existing = findMdiChild(fileName);
         if (existing) {
             mdiArea->setActiveSubWindow(existing);
             return;
         }

         MdiChild *child = createMdiChild();
         if (child->loadFile(fileName)) {
             statusBar()->showMessage(tr("File loaded"), 2000);
             child->show();
         } else {
             child->close();
         }
     }
 }

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

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

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

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

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

 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);
     pasteAct->setEnabled(hasMdiChild);
     closeAct->setEnabled(hasMdiChild);
     closeAllAct->setEnabled(hasMdiChild);
     tileAct->setEnabled(hasMdiChild);
     cascadeAct->setEnabled(hasMdiChild);
     nextAct->setEnabled(hasMdiChild);
     previousAct->setEnabled(hasMdiChild);
     separatorAct->setVisible(hasMdiChild);

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

 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(separatorAct);

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

     for (int i = 0; i < windows.size(); ++i) {
         MdiChild *child = qobject_cast<MdiChild *>(windows.at(i)->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);
         action->setCheckable(true);
         action ->setChecked(child == activeMdiChild());
         connect(action, SIGNAL(triggered()), windowMapper, SLOT(map()));
         windowMapper->setMapping(action, windows.at(i));
     }
 }

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

     connect(child, SIGNAL(copyAvailable(bool)),
             cutAct, SLOT(setEnabled(bool)));
     connect(child, SIGNAL(copyAvailable(bool)),
             copyAct, SLOT(setEnabled(bool)));

     return child;
 }

 void MainWindow::createActions()
 {
     newAct = new QAction(QIcon(":/images/new.png"), tr("&New"), this);
     newAct->setShortcut(tr("Ctrl+N"));
     newAct->setStatusTip(tr("Create a new file"));
     connect(newAct, SIGNAL(triggered()), this, SLOT(newFile()));

     openAct = new QAction(QIcon(":/images/open.png"), tr("&Open..."), this);
     openAct->setShortcut(tr("Ctrl+O"));
     openAct->setStatusTip(tr("Open an existing file"));
     connect(openAct, SIGNAL(triggered()), this, SLOT(open()));

     saveAct = new QAction(QIcon(":/images/save.png"), tr("&Save"), this);
     saveAct->setShortcut(tr("Ctrl+S"));
     saveAct->setStatusTip(tr("Save the document to disk"));
     connect(saveAct, SIGNAL(triggered()), this, SLOT(save()));

     saveAsAct = new QAction(tr("Save &As..."), this);
     saveAsAct->setStatusTip(tr("Save the document under a new name"));
     connect(saveAsAct, SIGNAL(triggered()), this, SLOT(saveAs()));

     exitAct = new QAction(tr("E&xit"), this);
     exitAct->setShortcut(tr("Ctrl+Q"));
     exitAct->setStatusTip(tr("Exit the application"));
     connect(exitAct, SIGNAL(triggered()), qApp, SLOT(closeAllWindows()));

     cutAct = new QAction(QIcon(":/images/cut.png"), tr("Cu&t"), this);
     cutAct->setShortcut(tr("Ctrl+X"));
     cutAct->setStatusTip(tr("Cut the current selection's contents to the "
                             "clipboard"));
     connect(cutAct, SIGNAL(triggered()), this, SLOT(cut()));

     copyAct = new QAction(QIcon(":/images/copy.png"), tr("&Copy"), this);
     copyAct->setShortcut(tr("Ctrl+C"));
     copyAct->setStatusTip(tr("Copy the current selection's contents to the "
                              "clipboard"));
     connect(copyAct, SIGNAL(triggered()), this, SLOT(copy()));

     pasteAct = new QAction(QIcon(":/images/paste.png"), tr("&Paste"), this);
     pasteAct->setShortcut(tr("Ctrl+V"));
     pasteAct->setStatusTip(tr("Paste the clipboard's contents into the current "
                               "selection"));
     connect(pasteAct, SIGNAL(triggered()), this, SLOT(paste()));

     closeAct = new QAction(tr("Cl&ose"), this);
     closeAct->setShortcut(tr("Ctrl+F4"));
     closeAct->setStatusTip(tr("Close the active window"));
     connect(closeAct, SIGNAL(triggered()),
             mdiArea, SLOT(closeActiveSubWindow()));

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

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

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

     nextAct = new QAction(tr("Ne&xt"), this);
     nextAct->setStatusTip(tr("Move the focus to the next window"));
     connect(nextAct, SIGNAL(triggered()),
             mdiArea, SLOT(activateNextSubWindow()));

     previousAct = new QAction(tr("Pre&vious"), this);
     previousAct->setStatusTip(tr("Move the focus to the previous "
                                  "window"));
     connect(previousAct, SIGNAL(triggered()),
             mdiArea, SLOT(activatePreviousSubWindow()));

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

     aboutAct = new QAction(tr("&About"), this);
     aboutAct->setStatusTip(tr("Show the application's About box"));
     connect(aboutAct, SIGNAL(triggered()), this, SLOT(about()));

     aboutQtAct = new QAction(tr("About &Qt"), this);
     aboutQtAct->setStatusTip(tr("Show the Qt library's About box"));
     connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
 }

 void MainWindow::createMenus()
 {
     fileMenu = menuBar()->addMenu(tr("&File"));
     fileMenu->addAction(newAct);
     fileMenu->addAction(openAct);
     fileMenu->addAction(saveAct);
     fileMenu->addAction(saveAsAct);
     fileMenu->addSeparator();
     QAction *action = fileMenu->addAction(tr("Switch layout direction"));
     connect(action, SIGNAL(triggered()), this, SLOT(switchLayoutDirection()));
     fileMenu->addAction(exitAct);

     editMenu = menuBar()->addMenu(tr("&Edit"));
     editMenu->addAction(cutAct);
     editMenu->addAction(copyAct);
     editMenu->addAction(pasteAct);

     windowMenu = menuBar()->addMenu(tr("&Window"));
     updateWindowMenu();
     connect(windowMenu, SIGNAL(aboutToShow()), this, SLOT(updateWindowMenu()));

     menuBar()->addSeparator();

     helpMenu = menuBar()->addMenu(tr("&Help"));
     helpMenu->addAction(aboutAct);
     helpMenu->addAction(aboutQtAct);
 }

 void MainWindow::createToolBars()
 {
     fileToolBar = addToolBar(tr("File"));
     fileToolBar->addAction(newAct);
     fileToolBar->addAction(openAct);
     fileToolBar->addAction(saveAct);

     editToolBar = addToolBar(tr("Edit"));
     editToolBar->addAction(cutAct);
     editToolBar->addAction(copyAct);
     editToolBar->addAction(pasteAct);
 }

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

 void MainWindow::readSettings()
 {
     QSettings settings("Trolltech", "MDI Example");
     QPoint pos = settings.value("pos", QPoint(200, 200)).toPoint();
     QSize size = settings.value("size", QSize(400, 400)).toSize();
     move(pos);
     resize(size);
 }

 void MainWindow::writeSettings()
 {
     QSettings settings("Trolltech", "MDI Example");
     settings.setValue("pos", pos());
     settings.setValue("size", size());
 }

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

 QMdiSubWindow *MainWindow::findMdiChild(const QString &fileName)
 {
     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)
         qApp->setLayoutDirection(Qt::RightToLeft);
     else
         qApp->setLayoutDirection(Qt::LeftToRight);
 }

 void MainWindow::setActiveSubWindow(QWidget *window)
 {
     if (!window)
         return;
     mdiArea->setActiveSubWindow(qobject_cast<QMdiSubWindow *>(window));
 }


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Qt 4.3.5