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, QImageReader::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);
        }

        printPdfAct = new QAction(tr("&Print as PDF"), this);
        connect(printPdfAct, SIGNAL(triggered()), scribbleArea, SLOT(printPdf()));

        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(printPdfAct);
        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()) {
            int ret = QMessageBox::warning(this, tr("Scribble"),
                              tr("The image has been modified.\n"
                                 "Do you want to save your changes?"),
                              QMessageBox::Yes | QMessageBox::Default,
                              QMessageBox::No,
                              QMessageBox::Cancel | QMessageBox::Escape);
            if (ret == QMessageBox::Yes) {
                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);
        }
    }