在使用MVVM架构时，我们会遇到各种各样的问题
其中一个很常见的问题就是如何在ViewModel层处理UI事件时在后台代码文件中不写任何代码。
在我这个例子中实现的是取得鼠标移动时的位置。
我的解决方法如下：
1、通过一个Behavior 取得关联对象的EventArgs,代码如下
1 public class ExtendedInvokeCommandAction : TriggerAction < FrameworkElement > 2 { 3 public static readonly DependencyProperty CommandProperty = DependencyProperty.Register( " Command " , typeof (ICommand), typeof (ExtendedInvokeCommandAction), new PropertyMetadata( null , CommandChangedCallback)); 4 public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register( " CommandParameter " , typeof ( object ), typeof (ExtendedInvokeCommandAction), new PropertyMetadata( null , CommandParameterChangedCallback)); 5 6 private static void CommandParameterChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e) 7 { 8 var invokeCommand = d as ExtendedInvokeCommandAction; 9 if (invokeCommand != null ) 10 invokeCommand.SetValue(CommandParameterProperty, e.NewValue); 11 } 12 13 private static void CommandChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e) 14 { 15 var invokeCommand = d as ExtendedInvokeCommandAction; 16 if (invokeCommand != null ) 17 invokeCommand.SetValue(CommandProperty, e.NewValue); 18 } 19 20 protected override void Invoke( object parameter) 21 { 22 if ( this .Command == null ) 23 return ; 24 25 if ( this .Command.CanExecute(parameter)) 26 { 27 var commandParameter = new ExtendedCommandParameter(parameter as EventArgs, this .AssociatedObject, 28 GetValue(CommandParameterProperty)); 29 this .Command.Execute(commandParameter); 30 } 31 } 32 33 #region public properties 34 35 public object CommandParameter 36 { 37 get { return GetValue(CommandParameterProperty); } 38 set { SetValue(CommandParameterProperty, value); } 39 } 40 41 public ICommand Command 42 { 43 get { return GetValue(CommandProperty) as ICommand; } 44 set { SetValue(CommandParameterProperty, value); } 45 } 46 47 #endregion 48 }
2、写一个类，包含的属性有事件源、EventArgs和对象，代码如下
1 public class ExtendedCommandParameter 2 { 3 public ExtendedCommandParameter(EventArgs eventArgs, FrameworkElement sender, object parameter) 4 { 5 EventArgs = eventArgs; 6 Sender = sender; 7 Parameter = parameter; 8 } 9 10 public EventArgs EventArgs { get ; private set ; } 11 public FrameworkElement Sender { get ; private set ; } 12 public object Parameter { get ; private set ; } 13 }
3、为对象添加Behavior
在我的这个例子中，我对Rectangle添加新建的类ExtendedInvokeCommandAction(即Behavior)
4、在ViewModel层把这个Behavior绑定到Command上，在这Command上选择一个事件，通过Comman调用这个事件
在我这个例子中，在ViewModle层我把MouseMove事件绑定到MouseMoved Command上，另外，如果需要的话，可以把任何对象绑定到CommandParameter,在我这个例子中，我把此View(变量名为userControl)绑定到了CommandParameter(不是必须的)
1 2 < Rectangle Fill = " #FF9B9BC5 " Height = " 200 " Stroke = " Black " Width = " 200 " > 3 < i:Interaction.Triggers > 4 < i:EventTrigger EventName = " MouseMove " > 5 < local:ExtendedInvokeCommandAction 6 Command = " {Binding MouseMoved} " 7 CommandParameter = " {Binding ElementName=userControl} " /> 8 </ i:EventTrigger > 9 </ i:Interaction.Triggers > 10 </ Rectangle > 11
5、在ViewModel层处理事件，代码如下
1 public class MainPageViewModel : INotifyPropertyChanged 2 { 3 public MainPageViewModel() 4 { 5 MouseMoved = new MainPageCommand( this ); // initialize the Command 6 } 7 8 // gets the position of the mouse 9 private void OnMouseMove(ExtendedCommandParameter commandParameter) 10 { 11 MouseEventArgs eventArgs; 12 13 // cast the EventArgs to the type you expect, according to the event you handle 14 // f.e. MouseMove Event gets you MouseEventArgs 15 // Click Event gets you RoutedEventArgs 16 if (commandParameter.EventArgs.GetType() == typeof (MouseEventArgs)) 17 { 18 eventArgs = commandParameter.EventArgs as MouseEventArgs; 19 if (commandParameter.Parameter != null ) 20 { 21 var view = commandParameter.Parameter as UIElement; 22 MousePosition = eventArgs.GetPosition(view).ToString(); 23 } 24 } 25 } 26 27 public MainPageCommand MouseMoved { get ; set ; } 28 private string _mousePosition; 29 public string MousePosition 30 { 31 get { return _mousePosition; } 32 set { _mousePosition = value; OnPropertyChanged( " MousePosition " ); } 33 } 34 35 #region INotifyChanged Members 36 37 public event PropertyChangedEventHandler PropertyChanged; 38 internal void OnPropertyChanged( string propertyName) 39 { 40 if ( this .PropertyChanged != null ) 41 { 42 this .PropertyChanged( this , new PropertyChangedEventArgs(propertyName)); 43 } 44 } 45 46 #endregion 47 48 #region command class 49 50 public class MainPageCommand : ICommand 51 { 52 public MainPageCommand(MainPageViewModel view) 53 { 54 _view = view; 55 } 56 57 private MainPageViewModel _view; 58 59 #region ICommand Members 60 61 public bool CanExecute( object parameter) 62 { 63 return true ; 64 } 65 66 public event EventHandler CanExecuteChanged; 67 68 public void Execute( object parameter) 69 { 70 // call the method to handle the event 71 _view.OnMouseMove(parameter as ExtendedCommandParameter); 72 } 73 74 #endregion 75 76 } 77 #endregion 78 79 }
如果需要，可以为每一个EventArgs建一个Behavior,只要把它绑定到Command上，然后Command代码中处理EventArgs就可以了
代码下载
