public MainWindowViewModel() { MessageBoxCommand = new DelegateCommand(async() => { var info = new MessageBoxNotification() { Title = "Confirm", Content = "aaaaaaaaaaaaaaaaaaaaaaaaaa\nbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\ncccccc", Icon = MessageBoxNotification.IconType.Question, Button = MessageBoxNotification.ButtonType.OkCancel }; var result = await MessageBoxRequest.RaiseAsync(info); Debug.WriteLine(result.Confirmed); }); var notify = new SubWindowNotification(); SubWindowShowCommand = new DelegateCommand(() => { SubWindowRequest.Raise(notify); }); SubWindowCloseCommand = new DelegateCommand(() => { notify.DoClosing(); }); }