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mainwindow.cpp Example File
mainwindows/sdi/mainwindow.cpp

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 #include <QtGui>

 #include "mainwindow.h"

 MainWindow::MainWindow()
 {
     init();
     setCurrentFile("");
 }

 MainWindow::MainWindow(const QString &fileName)
 {
     init();
     loadFile(fileName);
 }

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

 void MainWindow::newFile()
 {
     MainWindow *other = new MainWindow;
     other->move(x() + 40, y() + 40);
     other->show();
 }

 void MainWindow::open()
 {
     QString fileName = QFileDialog::getOpenFileName(this);
     if (!fileName.isEmpty()) {
         MainWindow *existing = findMainWindow(fileName);
         if (existing) {
             existing->show();
             existing->raise();
             existing->activateWindow();
             return;
         }

         if (isUntitled && textEdit->document()->isEmpty()
                 && !isWindowModified()) {
             loadFile(fileName);
         } else {
             MainWindow *other = new MainWindow(fileName);
             if (other->isUntitled) {
                 delete other;
                 return;
             }
             other->move(x() + 40, y() + 40);
             other->show();
         }
     }
 }

 bool MainWindow::save()
 {
     if (isUntitled) {
         return saveAs();
     } else {
         return saveFile(curFile);
     }
 }

 bool MainWindow::saveAs()
 {
     QString fileName = QFileDialog::getSaveFileName(this, tr("Save As"),
                                                     curFile);
     if (fileName.isEmpty())
         return false;

     return saveFile(fileName);
 }

 void MainWindow::about()
 {
    QMessageBox::about(this, tr("About SDI"),
             tr("The <b>SDI</b> example demonstrates how to write single "
                "document interface applications using Qt."));
 }

 void MainWindow::documentWasModified()
 {
     setWindowModified(true);
 }

 void MainWindow::init()
 {
     setAttribute(Qt::WA_DeleteOnClose);

     isUntitled = true;

     textEdit = new QTextEdit;
     setCentralWidget(textEdit);

     createActions();
     createMenus();
     createToolBars();
     createStatusBar();

     readSettings();

     connect(textEdit->document(), SIGNAL(contentsChanged()),
             this, SLOT(documentWasModified()));
 }

 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()));

     closeAct = new QAction(tr("&Close"), this);
     closeAct->setShortcut(tr("Ctrl+W"));
     closeAct->setStatusTip(tr("Close this window"));
     connect(closeAct, SIGNAL(triggered()), this, SLOT(close()));

     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()), textEdit, 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()), textEdit, 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()), textEdit, SLOT(paste()));

     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()));

     cutAct->setEnabled(false);
     copyAct->setEnabled(false);
     connect(textEdit, SIGNAL(copyAvailable(bool)),
             cutAct, SLOT(setEnabled(bool)));
     connect(textEdit, SIGNAL(copyAvailable(bool)),
             copyAct, SLOT(setEnabled(bool)));
 }

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

     editMenu = menuBar()->addMenu(tr("&Edit"));
     editMenu->addAction(cutAct);
     editMenu->addAction(copyAct);
     editMenu->addAction(pasteAct);

     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", "SDI 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", "SDI Example");
     settings.setValue("pos", pos());
     settings.setValue("size", size());
 }

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

 void MainWindow::loadFile(const QString &fileName)
 {

     QFile file(fileName);
     if (!file.open(QFile::ReadOnly | QFile::Text)) {
         QMessageBox::warning(this, tr("SDI"),
                              tr("Cannot read file %1:\n%2.")
                              .arg(fileName)
                              .arg(file.errorString()));
         return;
     }

     QTextStream in(&file);
     QApplication::setOverrideCursor(Qt::WaitCursor);
     textEdit->setPlainText(in.readAll());
     QApplication::restoreOverrideCursor();

     setCurrentFile(fileName);
     statusBar()->showMessage(tr("File loaded"), 2000);
 }

 bool MainWindow::saveFile(const QString &fileName)
 {
     QFile file(fileName);
     if (!file.open(QFile::WriteOnly | QFile::Text)) {
         QMessageBox::warning(this, tr("SDI"),
                              tr("Cannot write file %1:\n%2.")
                              .arg(fileName)
                              .arg(file.errorString()));
         return false;
     }

     QTextStream out(&file);
     QApplication::setOverrideCursor(Qt::WaitCursor);
     out << textEdit->toPlainText();
     QApplication::restoreOverrideCursor();

     setCurrentFile(fileName);
     statusBar()->showMessage(tr("File saved"), 2000);
     return true;
 }

 void MainWindow::setCurrentFile(const QString &fileName)
 {
     static int sequenceNumber = 1;

     isUntitled = fileName.isEmpty();
     if (isUntitled) {
         curFile = tr("document%1.txt").arg(sequenceNumber++);
     } else {
         curFile = QFileInfo(fileName).canonicalFilePath();
     }

     textEdit->document()->setModified(false);
     setWindowModified(false);

     setWindowTitle(tr("%1[*] - %2").arg(strippedName(curFile))
                                        .arg(tr("SDI")));
 }

 QString MainWindow::strippedName(const QString &fullFileName)
 {
     return QFileInfo(fullFileName).fileName();
 }

 MainWindow *MainWindow::findMainWindow(const QString &fileName)
 {
     QString canonicalFilePath = QFileInfo(fileName).canonicalFilePath();

     foreach (QWidget *widget, qApp->topLevelWidgets()) {
         MainWindow *mainWin = qobject_cast<MainWindow *>(widget);
         if (mainWin && mainWin->curFile == canonicalFilePath)
             return mainWin;
     }
     return 0;
 }


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Qt 4.3.5