qtbase/src/widgets/doc/snippets/code/src_gui_kernel_qapplication.cpp

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//! [0]
int main(int argc, char **argv)
{
#ifdef Q_WS_X11
    bool useGUI = getenv("DISPLAY") != 0;
#else
    bool useGUI = true;
#endif
    QApplication app(argc, argv, useGUI);

    if (useGUI) {
       // start GUI version
       ...
    } else {
       // start non-GUI version
       ...
    }
    return app.exec();
}
//! [0]


//! [1]
QApplication::setStyle(QStyleFactory::create("Fusion"));
//! [1]


//! [2]
int main(int argc, char *argv[])
{
    QApplication::setColorSpec(QApplication::ManyColor);
    QApplication app(argc, argv);
    ...
    return app.exec();
}
//! [2]


//! [3]
QSize MyWidget::sizeHint() const
{
    return QSize(80, 25).expandedTo(QApplication::globalStrut());
}
//! [3]


//! [4]
void showAllHiddenTopLevelWidgets()
{
    foreach (QWidget *widget, QApplication::topLevelWidgets()) {
        if (widget->isHidden())
            widget->show();
    }
}
//! [4]


//! [5]
void updateAllWidgets()
{
    foreach (QWidget *widget, QApplication::allWidgets())
        widget->update();
}
//! [5]


//! [6]
int main(int argc, char *argv[])
{
    QApplication::setDesktopSettingsAware(false);
    QApplication app(argc, argv);
    ...
    return app.exec();
}
//! [6]


//! [7]
if ((startPos - currentPos).manhattanLength() >=
        QApplication::startDragDistance())
    startTheDrag();
//! [7]


//! [8]
void MyApplication::commitData(QSessionManager& manager)
{
    if (manager.allowsInteraction()) {
        int ret = QMessageBox::warning(
                    mainWindow,
                    tr("My Application"),
                    tr("Save changes to document?"),
                    QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel);

        switch (ret) {
        case QMessageBox::Save:
            manager.release();
            if (!saveDocument())
                manager.cancel();
            break;
        case QMessageBox::Discard:
            break;
        case QMessageBox::Cancel:
        default:
            manager.cancel();
        }
    } else {
        // we did not get permission to interact, then
        // do something reasonable instead
    }
}
//! [8]


//! [9]
appname -session id
//! [9]


//! [10]
foreach (const QString &command, mySession.restartCommand())
    do_something(command);
//! [10]


//! [11]
foreach (const QString &command, mySession.discardCommand())
    do_something(command);
//! [11]


//! [12]
QWidget *widget = qApp->widgetAt(x, y);
if (widget)
    widget = widget->window();
//! [12]


//! [13]
QWidget *widget = qApp->widgetAt(point);
if (widget)
    widget = widget->window();
//! [13]