matrixion/third_party/SingleApplication-3.3.2/Windows.md

Windows Specific Implementations

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() 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 and the options parameter must include Mode::SecondaryNotification, See SingleApplication::Mode for more details.

Here is an example:

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

if( app.isPrimary() ) {
    QObject::connect(
        &app,
        &SingleApplication::instanceStarted,
        this,
        &App::instanceStarted
    );
}

void App::instanceStarted() {
    QApplication::setActiveWindow( [window/widget to set to the foreground] );
}