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mainwindow.cpp Example File
^{tools/plugandpaint/mainwindow.cpp}

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 #include "interfaces.h"
 #include "mainwindow.h"
 #include "paintarea.h"
 #include "plugindialog.h"

 #include <QPluginLoader>
 #include <QTimer>

 #include <QScrollArea>
 #include <QMessageBox>
 #include <QActionGroup>
 #include <QAction>
 #include <QMenu>
 #include <QMenuBar>
 #include <QFileDialog>
 #include <QColorDialog>
 #include <QInputDialog>
 #include <QApplication>

 MainWindow::MainWindow() :
     paintArea(new PaintArea),
     scrollArea(new QScrollArea)
 {
     scrollArea->setBackgroundRole(QPalette::Dark);
     scrollArea->setWidget(paintArea);
     setCentralWidget(scrollArea);

     createActions();
     createMenus();
     loadPlugins();

     setWindowTitle(tr("Plug & Paint"));

     if (!brushActionGroup->actions().isEmpty())
         brushActionGroup->actions().first()->trigger();

     QTimer::singleShot(500, this, SLOT(aboutPlugins()));
 }

 void MainWindow::open()
 {
     const QString fileName = QFileDialog::getOpenFileName(this,
                                                           tr("Open File"),
                                                           QDir::currentPath());
     if (!fileName.isEmpty()) {
         if (!paintArea->openImage(fileName)) {
             QMessageBox::information(this, tr("Plug & Paint"),
                                      tr("Cannot load %1.").arg(fileName));
             return;
         }
         paintArea->adjustSize();
     }
 }

 bool MainWindow::saveAs()
 {
     const QString initialPath = QDir::currentPath() + "/untitled.png";

     const QString fileName = QFileDialog::getSaveFileName(this, tr("Save As"),
                                                           initialPath);
     if (fileName.isEmpty()) {
         return false;
     } else {
         return paintArea->saveImage(fileName, "png");
     }
 }

 void MainWindow::brushColor()
 {
     const QColor newColor = QColorDialog::getColor(paintArea->brushColor());
     if (newColor.isValid())
         paintArea->setBrushColor(newColor);
 }

 void MainWindow::brushWidth()
 {
     bool ok;
     const int newWidth = QInputDialog::getInteger(this, tr("Plug & Paint"),
                                                   tr("Select brush width:"),
                                                   paintArea->brushWidth(),
                                                   1, 50, 1, &ok);
     if (ok)
         paintArea->setBrushWidth(newWidth);
 }

 void MainWindow::changeBrush()
 {
     QAction *action = qobject_cast<QAction *>(sender());
     BrushInterface *iBrush = qobject_cast<BrushInterface *>(action->parent());
     const QString brush = action->text();

     paintArea->setBrush(iBrush, brush);
 }

 void MainWindow::insertShape()
 {
     QAction *action = qobject_cast<QAction *>(sender());
     ShapeInterface *iShape = qobject_cast<ShapeInterface *>(action->parent());

     const QPainterPath path = iShape->generateShape(action->text(), this);
     if (!path.isEmpty())
         paintArea->insertShape(path);
 }

 void MainWindow::applyFilter()
 {
     QAction *action = qobject_cast<QAction *>(sender());
     FilterInterface *iFilter =
             qobject_cast<FilterInterface *>(action->parent());

     const QImage image = iFilter->filterImage(action->text(), paintArea->image(),
                                               this);
     paintArea->setImage(image);
 }

 void MainWindow::about()
 {
    QMessageBox::about(this, tr("About Plug & Paint"),
             tr("The <b>Plug & Paint</b> example demonstrates how to write Qt "
                "applications that can be extended through plugins."));
 }

 void MainWindow::aboutPlugins()
 {
     PluginDialog dialog(pluginsDir.path(), pluginFileNames, this);
     dialog.exec();
 }

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

     saveAsAct = new QAction(tr("&Save As..."), this);
     saveAsAct->setShortcut(tr("Ctrl+S"));
     connect(saveAsAct, SIGNAL(triggered()), this, SLOT(saveAs()));

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

     brushColorAct = new QAction(tr("&Brush Color..."), this);
     connect(brushColorAct, SIGNAL(triggered()), this, SLOT(brushColor()));

     brushWidthAct = new QAction(tr("&Brush Width..."), this);
     connect(brushWidthAct, SIGNAL(triggered()), this, SLOT(brushWidth()));

     brushActionGroup = new QActionGroup(this);

     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()));

     aboutPluginsAct = new QAction(tr("About &Plugins"), this);
     connect(aboutPluginsAct, SIGNAL(triggered()), this, SLOT(aboutPlugins()));
 }

 void MainWindow::createMenus()
 {
     fileMenu = menuBar()->addMenu(tr("&File"));
     fileMenu->addAction(openAct);
     fileMenu->addAction(saveAsAct);
     fileMenu->addSeparator();
     fileMenu->addAction(exitAct);

     brushMenu = menuBar()->addMenu(tr("&Brush"));
     brushMenu->addAction(brushColorAct);
     brushMenu->addAction(brushWidthAct);
     brushMenu->addSeparator();

     shapesMenu = menuBar()->addMenu(tr("&Shapes"));

     filterMenu = menuBar()->addMenu(tr("&Filter"));

     menuBar()->addSeparator();

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

 void MainWindow::loadPlugins()
 {
     foreach (QObject *plugin, QPluginLoader::staticInstances())
         populateMenus(plugin);

     pluginsDir = QDir(qApp->applicationDirPath());

 #if defined(Q_OS_WIN)
     if (pluginsDir.dirName().toLower() == "debug" || pluginsDir.dirName().toLower() == "release")
         pluginsDir.cdUp();
 #elif defined(Q_OS_MAC)
     if (pluginsDir.dirName() == "MacOS") {
         pluginsDir.cdUp();
         pluginsDir.cdUp();
         pluginsDir.cdUp();
     }
 #endif
     pluginsDir.cd("plugins");

     foreach (QString fileName, pluginsDir.entryList(QDir::Files)) {
         QPluginLoader loader(pluginsDir.absoluteFilePath(fileName));
         QObject *plugin = loader.instance();
         if (plugin) {
             populateMenus(plugin);
             pluginFileNames += fileName;
         }
     }

     brushMenu->setEnabled(!brushActionGroup->actions().isEmpty());
     shapesMenu->setEnabled(!shapesMenu->actions().isEmpty());
     filterMenu->setEnabled(!filterMenu->actions().isEmpty());
 }

 void MainWindow::populateMenus(QObject *plugin)
 {
     BrushInterface *iBrush = qobject_cast<BrushInterface *>(plugin);
     if (iBrush)
         addToMenu(plugin, iBrush->brushes(), brushMenu, SLOT(changeBrush()),
                   brushActionGroup);

     ShapeInterface *iShape = qobject_cast<ShapeInterface *>(plugin);
     if (iShape)
         addToMenu(plugin, iShape->shapes(), shapesMenu, SLOT(insertShape()));

     FilterInterface *iFilter = qobject_cast<FilterInterface *>(plugin);
     if (iFilter)
         addToMenu(plugin, iFilter->filters(), filterMenu, SLOT(applyFilter()));
 }

 void MainWindow::addToMenu(QObject *plugin, const QStringList &texts,
                            QMenu *menu, const char *member,
                            QActionGroup *actionGroup)
 {
     foreach (QString text, texts) {
         QAction *action = new QAction(text, plugin);
         connect(action, SIGNAL(triggered()), this, member);
         menu->addAction(action);

         if (actionGroup) {
             action->setCheckable(true);
             actionGroup->addAction(action);
         }
     }
 }