public Checkout() { InitializeComponent(); Loaded += (sender, args) => { Amount.Focus(); Amount.SelectAll(); }; KeyDown += (sender, args) => { if (args.Key == Key.Enter) { Model.OK(); } }; DataContextChanged += (sender, args) => { if (Model == null) { return; } Model.IsValid.Subscribe(x => { if (x) { Change.ClearValue(Label.ForegroundProperty); } else { Change.Foreground = Brushes.Red; } }); }; }