WPF showing dialog before main window

Question

How one can show dialog window (e.g. login / options etc.) before the main window?

Here is what I tried (it apparently has once worked, but not anymore):

Answer 1

If you put Application.Current.ShutdownMode = ShutdownMode.OnExplicitShutdown; into the constructor of the dialog, and add

protected override void OnClosed(EventArgs e) {
    base.OnClosed(e);
    Application.Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
}

into the dialog class, you don't need to worry about making any changes to the default behaviour of the application. This works great if you want to just snap a login screen into an already-existing app without tweaking the startup procedures.