private void cb_sensors_SelectionChanged(object sender, SelectionChangedEventArgs e) { var appvm = AppVM.GetCurrent(); SensorVM sensor = e.AddedItems[0] as SensorVM; // we assume comboBox so theres always a single selected item BoneVM bone = (BoneVM)DataContext; var arg = new Tuple <BoneVM, SensorVM>(bone, sensor); if (appvm.AssignSensorToBoneCommand.CanExecute(arg)) { appvm.AssignSensorToBoneCommand.Execute(arg); } ; }