mainwindow.cpp Example File
draganddrop/puzzle/mainwindow.cpp

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 #include <QtGui>
 #include <stdlib.h>

 #include "mainwindow.h"
 #include "pieceslist.h"
 #include "puzzlewidget.h"

 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)
 {
     setupMenus();
     setupWidgets();

     setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
     setWindowTitle(tr("Puzzle"));
 }

 void MainWindow::openImage(const QString &path)
 {
     QString fileName = path;

     if (fileName.isNull())
         fileName = QFileDialog::getOpenFileName(this,
             tr("Open Image"), "", "Image Files (*.png *.jpg *.bmp)");

     if (!fileName.isEmpty()) {
         QPixmap newImage;
         if (!newImage.load(fileName)) {
             QMessageBox::warning(this, tr("Open Image"),
                                   tr("The image file could not be loaded."),
                                   QMessageBox::Cancel);
             return;
         }
         puzzleImage = newImage;
         setupPuzzle();
     }
 }

 void MainWindow::setCompleted()
 {
     QMessageBox::information(this, tr("Puzzle Completed"),
         tr("Congratulations! You have completed the puzzle!\n"
            "Click OK to start again."),
         QMessageBox::Ok);

     setupPuzzle();
 }

 void MainWindow::setupPuzzle()
 {
     int size = qMin(puzzleImage.width(), puzzleImage.height());
     puzzleImage = puzzleImage.copy((puzzleImage.width() - size)/2,
         (puzzleImage.height() - size)/2, size, size).scaled(400,
             400, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);

     piecesList->clear();

     for (int y = 0; y < 5; ++y) {
         for (int x = 0; x < 5; ++x) {
             QPixmap pieceImage = puzzleImage.copy(x*80, y*80, 80, 80);
             piecesList->addPiece(pieceImage, QPoint(x, y));
         }
     }

     qsrand(QCursor::pos().x() ^ QCursor::pos().y());

     for (int i = 0; i < piecesList->count(); ++i) {
         if (int(2.0*qrand()/(RAND_MAX+1.0)) == 1) {
             QListWidgetItem *item = piecesList->takeItem(i);
             piecesList->insertItem(0, item);
         }
     }

     puzzleWidget->clear();
 }

 void MainWindow::setupMenus()
 {
     QMenu *fileMenu = menuBar()->addMenu(tr("&File"));

     QAction *openAction = fileMenu->addAction(tr("&Open..."));
     openAction->setShortcut(QKeySequence(tr("Ctrl+O")));

     QAction *exitAction = fileMenu->addAction(tr("E&xit"));
     exitAction->setShortcut(QKeySequence(tr("Ctrl+Q")));

     QMenu *gameMenu = menuBar()->addMenu(tr("&Game"));

     QAction *restartAction = gameMenu->addAction(tr("&Restart"));

     connect(openAction, SIGNAL(triggered()), this, SLOT(openImage()));
     connect(exitAction, SIGNAL(triggered()), qApp, SLOT(quit()));
     connect(restartAction, SIGNAL(triggered()), this, SLOT(setupPuzzle()));
 }

 void MainWindow::setupWidgets()
 {
     QFrame *frame = new QFrame;
     QHBoxLayout *frameLayout = new QHBoxLayout(frame);

     piecesList = new PiecesList;
     puzzleWidget = new PuzzleWidget;

     connect(puzzleWidget, SIGNAL(puzzleCompleted()),
             this, SLOT(setCompleted()), Qt::QueuedConnection);

     frameLayout->addWidget(piecesList);
     frameLayout->addWidget(puzzleWidget);
     setCentralWidget(frame);
 }