Handle opening a WPF application via protocol from another WPF application in a reusable manne

I open WPF application “A” via protocol from another WPF application “B”, I can handle this event in application “B”, using for example as in this code

if (activatedEventArgs != null)
{
    app.OnProtocolActivated(activatedEventArgs);
}

but it is triggered only on the first call of the opening event via protocol, I need that after the application has been opened via protocol and remains open that this event handler is triggered the next times.