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mainwindow.cpp Example File
^{widgets/scribble/mainwindow.cpp}

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 #include <QtGui>

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

 MainWindow::MainWindow()
 {
     scribbleArea = new ScribbleArea;
     setCentralWidget(scribbleArea);

     createActions();
     createMenus();

     setWindowTitle(tr("Scribble"));
     resize(500, 500);
 }

 void MainWindow::closeEvent(QCloseEvent *event)
 {
     if (maybeSave()) {
         event->accept();
     } else {
         event->ignore();
     }
 }

 void MainWindow::open()
 {
     if (maybeSave()) {
         QString fileName = QFileDialog::getOpenFileName(this,
                                    tr("Open File"), QDir::currentPath());
         if (!fileName.isEmpty())
             scribbleArea->openImage(fileName);
     }
 }

 void MainWindow::save()
 {
     QAction *action = qobject_cast<QAction *>(sender());
     QByteArray fileFormat = action->data().toByteArray();
     saveFile(fileFormat);
 }

 void MainWindow::penColor()
 {
     QColor newColor = QColorDialog::getColor(scribbleArea->penColor());
     if (newColor.isValid())
         scribbleArea->setPenColor(newColor);
 }

 void MainWindow::penWidth()
 {
     bool ok;
     int newWidth = QInputDialog::getInteger(this, tr("Scribble"),
                                             tr("Select pen width:"),
                                             scribbleArea->penWidth(),
                                             1, 50, 1, &ok);
     if (ok)
         scribbleArea->setPenWidth(newWidth);
 }

 void MainWindow::about()
 {
     QMessageBox::about(this, tr("About Scribble"),
             tr("<p>The <b>Scribble</b> example shows how to use QMainWindow as the "
                "base widget for an application, and how to reimplement some of "
                "QWidget's event handlers to receive the events generated for "
                "the application's widgets:</p><p> We reimplement the mouse event "
                "handlers to facilitate drawing, the paint event handler to "
                "update the application and the resize event handler to optimize "
                "the application's appearance. In addition we reimplement the "
                "close event handler to intercept the close events before "
                "terminating the application.</p><p> The example also demonstrates "
                "how to use QPainter to draw an image in real time, as well as "
                "to repaint widgets.</p>"));
 }

 void MainWindow::createActions()
 {
     openAct = new QAction(tr("&Open..."), this);
     openAct->setShortcut(tr("Ctrl+O"));
     connect(openAct, SIGNAL(triggered()), this, SLOT(open()));

     foreach (QByteArray format, QImageWriter::supportedImageFormats()) {
         QString text = tr("%1...").arg(QString(format).toUpper());

         QAction *action = new QAction(text, this);
         action->setData(format);
         connect(action, SIGNAL(triggered()), this, SLOT(save()));
         saveAsActs.append(action);
     }

     printAct = new QAction(tr("&Print..."), this);
     connect(printAct, SIGNAL(triggered()), scribbleArea, SLOT(print()));

     exitAct = new QAction(tr("E&xit"), this);
     exitAct->setShortcut(tr("Ctrl+Q"));
     connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

     penColorAct = new QAction(tr("&Pen Color..."), this);
     connect(penColorAct, SIGNAL(triggered()), this, SLOT(penColor()));

     penWidthAct = new QAction(tr("Pen &Width..."), this);
     connect(penWidthAct, SIGNAL(triggered()), this, SLOT(penWidth()));

     clearScreenAct = new QAction(tr("&Clear Screen"), this);
     clearScreenAct->setShortcut(tr("Ctrl+L"));
     connect(clearScreenAct, SIGNAL(triggered()),
             scribbleArea, SLOT(clearImage()));

     aboutAct = new QAction(tr("&About"), this);
     connect(aboutAct, SIGNAL(triggered()), this, SLOT(about()));

     aboutQtAct = new QAction(tr("About &Qt"), this);
     connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
 }

 void MainWindow::createMenus()
 {
     saveAsMenu = new QMenu(tr("&Save As"), this);
     foreach (QAction *action, saveAsActs)
         saveAsMenu->addAction(action);

     fileMenu = new QMenu(tr("&File"), this);
     fileMenu->addAction(openAct);
     fileMenu->addMenu(saveAsMenu);
     fileMenu->addAction(printAct);
     fileMenu->addSeparator();
     fileMenu->addAction(exitAct);

     optionMenu = new QMenu(tr("&Options"), this);
     optionMenu->addAction(penColorAct);
     optionMenu->addAction(penWidthAct);
     optionMenu->addSeparator();
     optionMenu->addAction(clearScreenAct);

     helpMenu = new QMenu(tr("&Help"), this);
     helpMenu->addAction(aboutAct);
     helpMenu->addAction(aboutQtAct);

     menuBar()->addMenu(fileMenu);
     menuBar()->addMenu(optionMenu);
     menuBar()->addMenu(helpMenu);
 }

 bool MainWindow::maybeSave()
 {
     if (scribbleArea->isModified()) {
        QMessageBox::StandardButton ret;
        ret = QMessageBox::warning(this, tr("Scribble"),
                           tr("The image has been modified.\n"
                              "Do you want to save your changes?"),
                           QMessageBox::Save | QMessageBox::Discard
                           | QMessageBox::Cancel);
         if (ret == QMessageBox::Save) {
             return saveFile("png");
         } else if (ret == QMessageBox::Cancel) {
             return false;
         }
     }
     return true;
 }

 bool MainWindow::saveFile(const QByteArray &fileFormat)
 {
     QString initialPath = QDir::currentPath() + "/untitled." + fileFormat;

     QString fileName = QFileDialog::getSaveFileName(this, tr("Save As"),
                                initialPath,
                                tr("%1 Files (*.%2);;All Files (*)")
                                .arg(QString(fileFormat.toUpper()))
                                .arg(QString(fileFormat)));
     if (fileName.isEmpty()) {
         return false;
     } else {
         return scribbleArea->saveImage(fileName, fileFormat);
     }
 }