Silverlight动画学习笔记（四）：以编程方式使用动画

（一）通过名称访问动画

（1）命名该动画对象，然后在代码中通过该名称引用它

（2）以使用集合来访问动画或动画的关键帧

      a）访问动画集合：Storyboard 具有 Children 属性，该属性允许您访问指定 Storyboard 中的所有动画对象

      b)访问关键帧集合:关键帧动画名称.KeyFrames[i]

      实例讲解： 

      <Canvas MouseLeftButtonDown="Handle_MouseDown"
  Width="600" Height="500" Background="Gray">
  <Canvas.Resources>
    <Storyboard x:Name="myStoryboard">
      <PointAnimationUsingKeyFrames
        x:Name="myPointAnimationUsingKeyFrames"
        Storyboard.TargetProperty="Center"
        Storyboard.TargetName="MyAnimatedEllipseGeometry"
        Duration="0:0:3">

        <DiscretePointKeyFrame KeyTime="0:0:0" />
        <LinearPointKeyFrame KeyTime="0:0:0.5" />
        <SplinePointKeyFrame KeySpline="0.6,0.0 0.9,0.00" KeyTime="0:0:2" />

      </PointAnimationUsingKeyFrames>

    </Storyboard>
  </Canvas.Resources>

  <Path Fill="Blue">
    <Path.Data>

      <!-- Describes an ellipse. -->
      <EllipseGeometry x:Name="MyAnimatedEllipseGeometry"
        Center="200,100" RadiusX="15" RadiusY="15" />
    </Path.Data>
  </Path>
</Canvas>

 

// Global variables that keep track of the end point
// of the last animation.
double lastX = 200;
double lastY = 100;
private void Handle_MouseDown(object sender, MouseEventArgs e)
{
    // Retrieve current mouse coordinates.
    double newX = e.GetPosition(null).X;
    double newY = e.GetPosition(null).Y;

    int i;
    for (i = 0; i < myPointAnimationUsingKeyFrames.KeyFrames.Count; i++)
    {
        PointKeyFrame keyFrame = myPointAnimationUsingKeyFrames.KeyFrames[i];
        if (keyFrame.GetType().Name == "DiscretePointKeyFrame")
        {
            keyFrame.SetValue(DiscretePointKeyFrame.ValueProperty, new Point(lastX, lastY));
        }
        else if (keyFrame.GetType().Name == "LinearPointKeyFrame")
        {    
            // Calculate the slope.
            double m = (newY - lastY) / (newX - lastX);

            // Calculate the y-intercept.
            double b = newY - (m * newX);

            // Set X to a third of the way to the end point.
            double intermediateX = lastX + (newX - lastX) / 3;

            // Find the value Y from X and the line formula.
            double intermediateY = (m * intermediateX) + b;

            // Set the keyframe value to the intermediate x and y value.
            keyFrame.SetValue(LinearPointKeyFrame.ValueProperty, 
                new Point(intermediateX, intermediateY));
        }
        else if (keyFrame.GetType().Name == "SplinePointKeyFrame")
        {
            keyFrame.SetValue(SplinePointKeyFrame.ValueProperty, new Point(newX, newY));
        }
    }
    myStoryboard.Stop();
    myStoryboard.Begin();
    lastX = newX;
    lastY = newY;
}

（二）动态更改TargetName

     动态更改 Storyboard.TargetName 属性最常见的情况是您想将同一动画应用到多个对象

     优点：当具有要应用相似动画的大量对象时，这特别有用。例如，您可能要显示几行图像并使用动画突出显示鼠标当前所指示的图像。为每个图像创建单独的 Storyboard 对象非常麻烦。重用同一 Storyboard 更为合适。

     实例讲解：这里讲同一动画动态赋给选中的矩形图形，给人的感觉是每个矩形都具有动画效果。这里要注意的是，在赋给当前图形动画时，要将上一个动画播放停止。

 

private void Start_Animation(object sender, MouseEventArgs e)
{

    // If the Storyboard is running and you try to change
    // properties of its animation objects programmatically, 
    // an error will occur.
    myStoryboard.Stop();

    // Get a reference to the rectangle that was clicked.
    Rectangle myRect = (Rectangle)sender;

    // Change the TargetName of the animation to the name of the
    // rectangle that was clicked.
    myDoubleAnimation.SetValue(Storyboard.TargetNameProperty, myRect.Name);

    // Begin the animation.
    myStoryboard.Begin();
}