Application Example

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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