Silverlight 行为(Behavior)

行为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。行为是一组相关操作的组合，它包含了触发器（监听某个事件或改变）和动作（完成适当的操作）的工作。例如，Deep Zoom功能由一些事件处理程序组成，允许通过鼠标按键和鼠标滚轮对Deep Zoom 图像进行平移和缩放。

想象一下在Canvas上如何让一个元素可以拥有拖放的行为，首先要创建一个派生自Behavior的类，Behavior是个泛型类，可以通过类型参数将行为限制到特定的元素，通常可以使用UIElement 或者是 FrameworkElement。

当用户按下鼠标左键，DragInCanvasBehavior开始拖拽操作，记录下元素左上角与鼠标指针之间的偏移量，并捕获鼠标。

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public class DragInCanvasBehavior : Behavior<UIElement>
{
protected override void OnAttached()
{
base.OnAttached();
//附加事件处理程序
this.Associatedobject.MouseLeftButtonDown += new MouseButtonEventHandler(Associatedobject_MouseLeftButtonDown);
this.Associatedobject.MouseMove += new MouseEventHandler(Associatedobject_MouseMove);
this.Associatedobject.MouseLeftButtonUp += new MouseButtonEventHandler(Associatedobject_MouseLeftButtonUp);
}
protected override void OnDetaching()
{
base.OnDetaching();
//分离事件处理程序
this.Associatedobject.MouseLeftButtonDown -= new MouseButtonEventHandler(Associatedobject_MouseLeftButtonDown);
this.Associatedobject.MouseMove -= new MouseEventHandler(Associatedobject_MouseMove);
this.Associatedobject.MouseLeftButtonUp -= new MouseButtonEventHandler(Associatedobject_MouseLeftButtonUp);
}
//记录当前元素所放置的Canvas
private Canvas canvas;
//记录当前元素是否正被拖拽
private bool isDragging = false;
//当鼠标左键按下的时候，记录单击所在的准确位置
private Point mouSEOffset;
private void Associatedobject_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
//找到Canvas
if (canvas == null)
{
canvas = (Canvas)VisualTreeHelper.GetParent(this.Associatedobject);
}
//拖拽模式开始
isDragging = true;
//获取鼠标单击时相对于元素的位置
//因此元素左上角的坐标为(0, 0)
mouSEOffset = e.GetPosition(Associatedobject);
//捕获鼠标，这样即使用户突然将鼠标指针拽到元素外，仍然可以接收到MouseMove事件
Associatedobject.CaptureMouse();
}
private void Associatedobject_MouseMove(object sender, MouseEventArgs e)
{
if (isDragging)
{
//鼠标指针相对于Canvas的位置
Point point = e.GetPosition(canvas);
//重定位元素
Canvas.SetLeft(Associatedobject, point.X - mouSEOffset.X);
Canvas.SetTop(Associatedobject, point.Y - mouSEOffset.Y);
}
}
private void Associatedobject_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
if (isDragging)
{
Associatedobject.ReleaseMouseCapture();
isDragging = false;
}
}
}

接下来只要简单的附加到Canvas中的任何元素，就可以使用这个行为。

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@H_162_502@<UserControl x:Class="SilverlightApplication1.Behaviors.BehaviorSample"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:custom="clr-namespace:SilverlightApplication1.Behaviors"
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400"@H_162_502@>
@H_162_502@<Canvas@H_162_502@>
@H_162_502@<Rectangle Canvas.Left="10" Canvas.Top="10" Width="40" Height="60" Fill="Yellow" @H_162_502@/>
@H_162_502@<Ellipse Canvas.Left="10" Canvas.Top="70" Fill="Blue" Width="80" Height="60"@H_162_502@>
@H_162_502@<i:Interaction.Behaviors@H_162_502@>
@H_162_502@<custom:DragInCanvasBehavior @H_162_502@/>
@H_162_502@</i:Interaction.Behaviors@H_162_502@>
@H_162_502@</Ellipse@H_162_502@>
@H_162_502@<Ellipse Canvas.Left="80" Canvas.Top="70" Fill="OrangeRed" Width="40" Height="70"@H_162_502@>
@H_162_502@<i:Interaction.Behaviors@H_162_502@>
@H_162_502@<custom:DragInCanvasBehavior @H_162_502@/>
@H_162_502@</i:Interaction.Behaviors@H_162_502@>
@H_162_502@</Ellipse@H_162_502@>
@H_162_502@</Canvas@H_162_502@>
@H_162_502@</UserControl@H_162_502@>

本文链接地址为：http://blog.csdn.net/fan_ken/article/details/6737495

Silverlight 行为(Behavior)

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