Canvas布局下使用附加属性使控件岁鼠标移动

定义附加属性
 public class MoveBehavior
    {
        public static readonly DependencyProperty IsMoveAbleProperty = DependencyProperty.RegisterAttached("IsMoveAble", typeof(bool),
            typeof(MoveBehavior),new PropertyMetadata(false, OnEnableMoveChanged));

        public static bool GetIsMoveAble(DependencyObject obj)
        {
            return (bool)obj.GetValue(IsMoveAbleProperty);
        }

        public static void SetIsMoveAble(DependencyObject obj,bool value)
        {
            obj.SetValue(IsMoveAbleProperty, value);
        }
        public static void OnEnableMoveChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var element = d as FrameworkElement;
            if (d!=null&& GetIsMoveAble(d))
            {
                element.PreviewMouseDown += Element_MouseDown;
                element.PreviewMouseUp += Element_MouseUp;
                element.PreviewMouseMove += Element_MouseMove;           
            }            
        }

        private static bool isCaptured = false;
        private static void Element_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {            
            var element = sender as FrameworkElement;
            if (element == null) return;
             var parent = VisualTreeHelper.GetParent(element) as FrameworkElement;
            if (parent == null) return;
            if (!isCaptured) return;
            var p = e.GetPosition(parent);
            Canvas.SetTop(element, p.Y - element.ActualWidth / 2);
            Canvas.SetLeft(element, p.X - element.ActualHeight / 2);
        }

        private static void Element_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            isCaptured = false;
            (sender as FrameworkElement).ReleaseMouseCapture();
        }

        private static void Element_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            isCaptured = true;
            (sender as FrameworkElement).CaptureMouse();
        }
    }

<Canvas>
        <Ellipse Width="50" Height="50" Fill="Red" x:Name="el"
               local:MoveBehavior.IsMoveAble="True"  ></Ellipse>
        <Button local:MoveBehavior.IsMoveAble="False" Click="Button_Click_1" Content="Button" Canvas.Left="303.112" Canvas.Top="196.833" Width="75" Height="47.005"/>
    </Canvas>