Qt 5.11 | Qt Widgets | Application Example | mainwindow.cpp Example File

Qt 5.11.3 Reference Documentation

# mainwindow.cpp Example File

mainwindows/application/mainwindow.cpp

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      #include <QtWidgets>

      #include "mainwindow.h"

      MainWindow::MainWindow()
          : textEdit(new QPlainTextEdit)
      {
          setCentralWidget(textEdit);

          createActions();
          createStatusBar();

          readSettings();

          connect(textEdit->document(), &QTextDocument::contentsChanged,
                  this, &MainWindow::documentWasModified);

      #ifndef QT_NO_SESSIONMANAGER
          QGuiApplication::setFallbackSessionManagementEnabled(false);
          connect(qApp, &QGuiApplication::commitDataRequest,
                  this, &MainWindow::commitData);
      #endif

          setCurrentFile(QString());
          setUnifiedTitleAndToolBarOnMac(true);
      }

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

      void MainWindow::newFile()
      {
          if (maybeSave()) {
              textEdit->clear();
              setCurrentFile(QString());
          }
      }

      void MainWindow::open()
      {
          if (maybeSave()) {
              QString fileName = QFileDialog::getOpenFileName(this);
              if (!fileName.isEmpty())
                  loadFile(fileName);
          }
      }

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

      bool MainWindow::saveAs()
      {
          QFileDialog dialog(this);
          dialog.setWindowModality(Qt::WindowModal);
          dialog.setAcceptMode(QFileDialog::AcceptSave);
          if (dialog.exec() != QDialog::Accepted)
              return false;
          return saveFile(dialog.selectedFiles().first());
      }

      void MainWindow::about()
      {
         QMessageBox::about(this, tr("About Application"),
                  tr("The <b>Application</b> example demonstrates how to "
                     "write modern GUI applications using Qt, with a menu bar, "
                     "toolbars, and a status bar."));
      }

      void MainWindow::documentWasModified()
      {
          setWindowModified(textEdit->document()->isModified());
      }

      void MainWindow::createActions()
      {

          QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
          QToolBar *fileToolBar = addToolBar(tr("File"));
          const QIcon newIcon = QIcon::fromTheme("document-new", QIcon(":/images/new.png"));
          QAction *newAct = new QAction(newIcon, tr("&New"), this);
          newAct->setShortcuts(QKeySequence::New);
          newAct->setStatusTip(tr("Create a new file"));
          connect(newAct, &QAction::triggered, this, &MainWindow::newFile);
          fileMenu->addAction(newAct);
          fileToolBar->addAction(newAct);

          const QIcon openIcon = QIcon::fromTheme("document-open", QIcon(":/images/open.png"));
          QAction *openAct = new QAction(openIcon, tr("&Open..."), this);
          openAct->setShortcuts(QKeySequence::Open);
          openAct->setStatusTip(tr("Open an existing file"));
          connect(openAct, &QAction::triggered, this, &MainWindow::open);
          fileMenu->addAction(openAct);
          fileToolBar->addAction(openAct);

          const QIcon saveIcon = QIcon::fromTheme("document-save", QIcon(":/images/save.png"));
          QAction *saveAct = new QAction(saveIcon, tr("&Save"), this);
          saveAct->setShortcuts(QKeySequence::Save);
          saveAct->setStatusTip(tr("Save the document to disk"));
          connect(saveAct, &QAction::triggered, this, &MainWindow::save);
          fileMenu->addAction(saveAct);
          fileToolBar->addAction(saveAct);

          const QIcon saveAsIcon = QIcon::fromTheme("document-save-as");
          QAction *saveAsAct = fileMenu->addAction(saveAsIcon, tr("Save &As..."), this, &MainWindow::saveAs);
          saveAsAct->setShortcuts(QKeySequence::SaveAs);
          saveAsAct->setStatusTip(tr("Save the document under a new name"));

          fileMenu->addSeparator();

          const QIcon exitIcon = QIcon::fromTheme("application-exit");
          QAction *exitAct = fileMenu->addAction(exitIcon, tr("E&xit"), this, &QWidget::close);
          exitAct->setShortcuts(QKeySequence::Quit);
          exitAct->setStatusTip(tr("Exit the application"));

          QMenu *editMenu = menuBar()->addMenu(tr("&Edit"));
          QToolBar *editToolBar = addToolBar(tr("Edit"));
      #ifndef QT_NO_CLIPBOARD
          const QIcon cutIcon = QIcon::fromTheme("edit-cut", QIcon(":/images/cut.png"));
          QAction *cutAct = new QAction(cutIcon, tr("Cu&t"), this);
          cutAct->setShortcuts(QKeySequence::Cut);
          cutAct->setStatusTip(tr("Cut the current selection's contents to the "
                                  "clipboard"));
          connect(cutAct, &QAction::triggered, textEdit, &QPlainTextEdit::cut);
          editMenu->addAction(cutAct);
          editToolBar->addAction(cutAct);

          const QIcon copyIcon = QIcon::fromTheme("edit-copy", QIcon(":/images/copy.png"));
          QAction *copyAct = new QAction(copyIcon, tr("&Copy"), this);
          copyAct->setShortcuts(QKeySequence::Copy);
          copyAct->setStatusTip(tr("Copy the current selection's contents to the "
                                   "clipboard"));
          connect(copyAct, &QAction::triggered, textEdit, &QPlainTextEdit::copy);
          editMenu->addAction(copyAct);
          editToolBar->addAction(copyAct);

          const QIcon pasteIcon = QIcon::fromTheme("edit-paste", QIcon(":/images/paste.png"));
          QAction *pasteAct = new QAction(pasteIcon, tr("&Paste"), this);
          pasteAct->setShortcuts(QKeySequence::Paste);
          pasteAct->setStatusTip(tr("Paste the clipboard's contents into the current "
                                    "selection"));
          connect(pasteAct, &QAction::triggered, textEdit, &QPlainTextEdit::paste);
          editMenu->addAction(pasteAct);
          editToolBar->addAction(pasteAct);

          menuBar()->addSeparator();

      #endif // !QT_NO_CLIPBOARD

          QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));
          QAction *aboutAct = helpMenu->addAction(tr("&About"), this, &MainWindow::about);
          aboutAct->setStatusTip(tr("Show the application's About box"));

          QAction *aboutQtAct = helpMenu->addAction(tr("About &Qt"), qApp, &QApplication::aboutQt);
          aboutQtAct->setStatusTip(tr("Show the Qt library's About box"));

      #ifndef QT_NO_CLIPBOARD
          cutAct->setEnabled(false);
          copyAct->setEnabled(false);
          connect(textEdit, &QPlainTextEdit::copyAvailable, cutAct, &QAction::setEnabled);
          connect(textEdit, &QPlainTextEdit::copyAvailable, copyAct, &QAction::setEnabled);
      #endif // !QT_NO_CLIPBOARD
      }

      void MainWindow::createStatusBar()
      {
          statusBar()->showMessage(tr("Ready"));
      }

      void MainWindow::readSettings()
      {
          QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());
          const QByteArray geometry = settings.value("geometry", QByteArray()).toByteArray();
          if (geometry.isEmpty()) {
              const QRect availableGeometry = QApplication::desktop()->availableGeometry(this);
              resize(availableGeometry.width() / 3, availableGeometry.height() / 2);
              move((availableGeometry.width() - width()) / 2,
                   (availableGeometry.height() - height()) / 2);
          } else {
              restoreGeometry(geometry);
          }
      }

      void MainWindow::writeSettings()
      {
          QSettings settings(QCoreApplication::organizationName(), QCoreApplication::applicationName());
          settings.setValue("geometry", saveGeometry());
      }

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

      void MainWindow::loadFile(const QString &fileName)
      {
          QFile file(fileName);
          if (!file.open(QFile::ReadOnly | QFile::Text)) {
              QMessageBox::warning(this, tr("Application"),
                                   tr("Cannot read file %1:\n%2.")
                                   .arg(QDir::toNativeSeparators(fileName), file.errorString()));
              return;
          }

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

          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("Application"),
                                   tr("Cannot write file %1:\n%2.")
                                   .arg(QDir::toNativeSeparators(fileName),
                                        file.errorString()));
              return false;
          }

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

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

      void MainWindow::setCurrentFile(const QString &fileName)
      {
          curFile = fileName;
          textEdit->document()->setModified(false);
          setWindowModified(false);

          QString shownName = curFile;
          if (curFile.isEmpty())
              shownName = "untitled.txt";
          setWindowFilePath(shownName);
      }

      QString MainWindow::strippedName(const QString &fullFileName)
      {
          return QFileInfo(fullFileName).fileName();
      }
      #ifndef QT_NO_SESSIONMANAGER
      void MainWindow::commitData(QSessionManager &manager)
      {
          if (manager.allowsInteraction()) {
              if (!maybeSave())
                  manager.cancel();
          } else {
              // Non-interactive: save without asking
              if (textEdit->document()->isModified())
                  save();
          }
      }
      #endif