Silverlight 行為(Behavior)

 

        行為的目的在於封裝部分UI功能，那樣就可以直接應用於元素而不用寫任何代碼。行為是一組相關操作的組合，它包含了觸發器（監聽某個事件或改變）和動作（完成適當的操作）的工作。例如，Deep Zoom功能由一些事件處理常式組成，允許通過滑鼠按鍵和滑鼠滾輪對Deep Zoom 映像進行平移和縮放。

        想象一下在Canvas上如何讓一個元素可以擁有拖放的行為，首先要建立一個派生自Behavior的類，Behavior是個泛型類，可以通過型別參數將行為限制到特定的元素，通常可以使用UIElement 或者是 FrameworkElement。

        當使用者按下滑鼠左鍵，DragInCanvasBehavior開始拖拽操作，記錄下元素左上方與滑鼠指標之間的位移量，並捕獲滑鼠。

    public class DragInCanvasBehavior : Behavior<UIElement>    {        protected override void OnAttached()        {            base.OnAttached();            //附加事件處理常式            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();            //分離事件處理常式            this.AssociatedObject.MouseLeftButtonDown -= new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonDown);            this.AssociatedObject.MouseMove -= new MouseEventHandler(AssociatedObject_MouseMove);            this.AssociatedObject.MouseLeftButtonUp -= new MouseButtonEventHandler(AssociatedObject_MouseLeftButtonUp);        }        //記錄當前元素所放置的Canvas        private Canvas canvas;        //記錄當前元素是否正被拖拽        private bool isDragging = false;        //當滑鼠左鍵按下的時候，記錄單擊所在的準確位置        private Point mouseOffset;        private void AssociatedObject_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)        {            //找到Canvas            if (canvas == null)            {                canvas = (Canvas)VisualTreeHelper.GetParent(this.AssociatedObject);            }            //拖拽模式開始            isDragging = true;            //擷取按一下滑鼠時相對於元素的位置            //因此元素左上方的座標為(0, 0)            mouseOffset = e.GetPosition(AssociatedObject);            //捕獲滑鼠，這樣即使使用者突然將滑鼠指標拽到元素外，仍然可以接收到MouseMove事件            AssociatedObject.CaptureMouse();        }        private void AssociatedObject_MouseMove(object sender, MouseEventArgs e)        {            if (isDragging)            {                //滑鼠指標相對於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;            }        }    }

接下來只要簡單的附加到Canvas中的任何元素，就可以使用這個行為。

<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">    <Canvas>        <Rectangle Canvas.Left="10" Canvas.Top="10" Width="40" Height="60" Fill="Yellow" />        <Ellipse Canvas.Left="10" Canvas.Top="70" Fill="Blue" Width="80" Height="60">            <i:Interaction.Behaviors>                <custom:DragInCanvasBehavior />            </i:Interaction.Behaviors>        </Ellipse>        <Ellipse Canvas.Left="80" Canvas.Top="70" Fill="OrangeRed" Width="40" Height="70">            <i:Interaction.Behaviors>                <custom:DragInCanvasBehavior />            </i:Interaction.Behaviors>        </Ellipse>    </Canvas></UserControl>