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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));
     }