Silverlight中的Behavior-蒲公英云

Silverlight中的Behavior

上次写了关于Trigger和Action的文章（Silverlight中的Action和Trigger），这次写一个Behavior的。Behavior的目的在于封装部分UI功能，那样就可以直接应用于元素而不用写任何代码。Behavior是一组相关操作的组合，它包含了Trigger和Action的工作。简单的说就是Trigger和Action的合体。

听说过Behavior的人一说到Behavior很容易想到拖动效果，这里我就做一个简单的在Canvas里的拖动行为。创建自定义Behavior需要从Behavior继承，并覆盖OnAttached和OnDetaching方法（和Trigger差不多）。还是用代码说话方便。

新建一个Behavior如下：

1: public class Behavior1 : Behavior<Shape>
2: {
3:     private Canvas _canvas;
4:     private bool _isDraging;
5:     private Point _originalMousePosition;
6: 
7:     public Behavior1()
8:     {
9:         _isDraging = false;
10:     }
11: 
12:     protected override void OnAttached()
13:     {
14:         base.OnAttached();
15:         this.AssociatedObject.MouseLeftButtonDown += new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonDown);
16:         this.AssociatedObject.MouseMove += new MouseEventHandler(AssociatedObject_MouseMove);
17:         this.AssociatedObject.MouseLeftButtonUp += new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonUp);
18:     }
19: 
20:     protected override void OnDetaching()
21:     {
22:         base.OnDetaching();
23:         this.AssociatedObject.MouseLeftButtonDown -= new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonDown);
24:         this.AssociatedObject.MouseMove -= new MouseEventHandler(AssociatedObject_MouseMove);
25:         this.AssociatedObject.MouseLeftButtonUp -= new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonUp);
26:     }
27: 
28:     private void AssociatedObject_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
29:     {
30:         _canvas = (Canvas)VisualTreeHelper.GetParent(this.AssociatedObject);
31:         _originalMousePosition = e.GetPosition(_canvas);
32:         _isDraging = true;
33:         this.AssociatedObject.CaptureMouse();
34:     }
35: 
36:     private void AssociatedObject_MouseMove(object sender, MouseEventArgs e)
37:     {
38:         if (_isDraging)
39:         {
40:             //get the current mouse position
41:             Point currentMousePosition = e.GetPosition(_canvas);
42:             //calculate the current position of the shape
43:             this.AssociatedObject.SetValue(Canvas.LeftProperty, ((double)this.AssociatedObject.GetValue(Canvas.LeftProperty)) + (currentMousePosition.X - _originalMousePosition.X));
44:             this.AssociatedObject.SetValue(Canvas.TopProperty, ((double)this.AssociatedObject.GetValue(Canvas.TopProperty)) + (currentMousePosition.Y - _originalMousePosition.Y));
45:             //update original mouse position
46:             _originalMousePosition = currentMousePosition;
47:         }
48:     }
49: 
50:     private void AssociatedObject_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
51:     {
52:         _isDraging = false;
53:         this.AssociatedObject.ReleaseMouseCapture();
54:     }
55: }

OnAttached里面注册MouseLeftButtonDown，MouseMove，MouseLeftButtonUp三个事件，OnDetaching里面取消注册。MouseLeftButtonDown事件获取Canvas和原始坐标，并设置开始拖动的标志；MouseMove事件不停的计算当前坐标与原始坐标的差值，并更新到Shape的坐标，从而实现移动（坐标的计算方法这里不多说）；MouseLeftButtonUp结束拖动。这三个事件处理方法实际上可以看成三个Action，而Behavior本身可以看成一个Trigger。

下面该使用这个Behavior了。

因为是在Canvas上的拖动，所以要有一个Canvas，然后在上面放一个矩形和一个椭圆：

1: <Canvas x:Name="LayoutRoot" Background="White">
2:     <Rectangle Fill="#FFF4F4F5" Height="76" Canvas.Left="82" Stroke="Black" Canvas.Top="78" Width="81">
3:         <i:Interaction.Behaviors>
4:             <local:Behavior1/>
5:         </i:Interaction.Behaviors>
6:     </Rectangle>
7:     <Ellipse Fill="#FFF4F4F5" Height="76" Canvas.Left="221" Stroke="Black" Canvas.Top="154" Width="79">
8:         <i:Interaction.Behaviors>
9:             <local:Behavior1/>
10:         </i:Interaction.Behaviors>
11:     </Ellipse>
12: </Canvas>