Silverlight中的Behavior

ゝ一纸荒年。 2021-11-05 00:58 313阅读 0赞

上次写了关于Trigger和Action的文章（[Silverlight中的Action和Trigger][Silverlight_Action_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<DependencyObject>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;

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>

给它们分别应用上同一个Behavior，然后运行。结果很明显，两个Shape都能拖动了。

Behavior是个好东西，好处就不用说了，显而易见。其实在Blend（做Silverlight界面的）中已经预定义了不少Behaviors，在[Microsoft Expression Gallery][]也可以获得他人的或共享自己的Behavior。

附上上面的源代码

参考资料：

[http://hi.baidu.com/biongiser/item/6c3509355f9b49f32784f40b][http_hi.baidu.com_biongiser_item_6c3509355f9b49f32784f40b]

[http://kb.cnblogs.com/a/2253240/][http_kb.cnblogs.com_a_2253240]

转载于:https://www.cnblogs.com/sosowjb/archive/2012/06/29/2568957.html

[Silverlight_Action_Trigger]: http://www.cnblogs.com/sosowjb/archive/2012/06/28/2566615.html
[Microsoft Expression Gallery]: http://gallery.expression.microsoft.com/
[http_hi.baidu.com_biongiser_item_6c3509355f9b49f32784f40b]: http://hi.baidu.com/biongiser/item/6c3509355f9b49f32784f40b
[http_kb.cnblogs.com_a_2253240]: http://kb.cnblogs.com/a/2253240/