SingleApplication/Windows.md

Windows Specifics

Setting the foreground window

In the instanceStarted() example in the README we demonstrated how an application can bring it's primary instance window whenever a second copy of the application is started.

On Windows the ability to bring the application windows to the foreground is restricted, see [AllowSetForegroundWindow()][https://msdn.microsoft.com/en-us/library/windows/desktop/ms632668.aspx] for more details.

The background process (the primary instance) can bring its windows to the foreground if it is allowed by the current foreground process (the secondary instance). To bypass this SingleApplication must be initialized with the allowSecondary parameter set to true .

If the widget is minimized to Windows task bar, QWidget::raise() or QWidget::show() can not bring it to the front, you have to use Windows API ShowWindow() .

Here is an example, you can find this project in the example directory:

SingleApplication app(argc, argv, true);
if ( app.isSecondary() ) {
    // This API requires LIBS += User32.lib to be added to the project
    AllowSetForegroundWindow( DWORD( app.primaryPid() ) );

    objApp.sendMessage("SHOW_WINDOW");

    return 0;
}

QWidget* widget = new QWidget;

QObject::connect(&app, &SingleApplication::receivedMessage,
                 widget, [widget] () { RaiseWidget(widget); } );

void RaiseWidget(QWidget* widget) {

    HWND hwnd = (HWND)widget->winId();

    // check if widget is minimized
    if (::IsIconic(hwnd)) {
        ::ShowWindow(hwnd, SW_RESTORE);
    }

    ::SetForegroundWindow(hwnd);
}