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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;
     }