silverlight做一些复杂动画时，不可能所有的动画都事先用Blend之类的设计工具"画"好(或者在设计期就在vs里编好)，很多时候我们希望在运行时能动态控制动画，或者凭空动态创建一段动画.
sl3.0的官方sdk文档里有一节"以编程方式使用动画"讲的就是这个，今天研究了下整理分析于此:
对于事先"画"好(或者称之为在设计期准备好的动画)，我们可以在运行时通过名字获取动画引用，进而改变某些属性:
1.示例1(代码来自sdk,以下同)，运行时动态改变动画的To属性值，从而实现鼠标点击跟随效果
Xaml部分:
Change.Xaml
<UserControl x:Class="AnimationControl.Change"
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"
mc:Ignorable="d" >
<Canvas MouseLeftButtonDown="Handle_MouseDown" Background="DarkSeaGreen" Width="400" Height="300" Cursor="Hand">
<Canvas.Resources>
<Storyboard x:Name="myStoryboard">
<PointAnimation x:Name="myPointAnimation" Storyboard.TargetProperty="Center" Storyboard.TargetName="MyAnimatedEllipseGeometry" Duration="0:0:0.5"/>
</Storyboard>
</Canvas.Resources>
<TextBlock Text="请在圆形之外的空白处点击" Foreground="White" FontStretch="Normal" FontWeight="Bold" FontSize="18" TextAlignment="Center" Canvas.Left="100" Canvas.Top="130" Cursor="Hand" Opacity="0.5">
</TextBlock>
<Path Fill="Blue">
<Path.Data>
<EllipseGeometry x:Name="MyAnimatedEllipseGeometry" Center="200,100" RadiusX="15" RadiusY="15" />
</Path.Data>
</Path>
</Canvas>
</UserControl>布局很简单，一个Canvas上放了一个圆，并创建了一个动画myPointAnimation
CS部分：
Change.Xaml.Cs
1using System.Windows;
2using System.Windows.Controls;
3using System.Windows.Input;
4
5namespace AnimationControl
6
{
7
public partial class Change : UserControl
8
{
9 public Change()
10 {
11 InitializeComponent();
12
}
13
14 private void Handle_MouseDown(object sender, MouseButtonEventArgs e)
15 {
16 //取得鼠标当前在Canvas中的点击坐标
17 double newX = e.GetPosition(sender as UIElement).X;
18 double newY = e.GetPosition(sender as UIElement).Y;
19 Point myPoint = new Point();
20 myPoint.X = newX;
21 myPoint.Y = newY;
22
23 //动态设置动画的To属性值
24 myPointAnimation.To = myPoint;
25
26 //播放
27 myStoryboard.Begin();
28 }
29
30 }
31
}
32
代码不长，一看就明，获取鼠标的点击坐标后，赋值为动画myPointAnimation的To属性(即移动后的目标坐标值)，然后播放
2.示例2，有时候很多对象可能会引用到同一效果的动画，每个对象都去创建一个动画太浪费，这时候我们可以把类似的动画通过改变TartgetName值得以重用
但有一点要注意：因为同一个动画同一时间只能有一个Target，所以如果给这个动画赋值了TartgetName，并且该动画正在播放的过程中，又用代码给动画的TargetName属性赋值另外一个对象，并要求播放，显示是会失效的。(实际测试中发现，虽然这样不会抛出任何异常)
为避免这种错误的发生，sdk中的示例代码提示我们可以这样做：
Xaml部分：
Code
1<UserControl x:Class="AnimationControl.Change2"
2 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
5 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
6 mc:Ignorable="d"
7 >
8
9 <StackPanel Orientation="Horizontal">
10 <StackPanel.Resources>
11 <Storyboard x:Name="myStoryboard1" Completed="Storyboard_Completed">
12 <DoubleAnimation x:Name="myDoubleAnimation1" Storyboard.TargetProperty="Opacity" From="1.0" To="0.0" Duration="0:0:2" AutoReverse="True" />
13 </Storyboard>
14 <Storyboard x:Name="myStoryboard2" Completed="Storyboard_Completed">
15 <DoubleAnimation x:Name="myDoubleAnimation2" Storyboard.TargetProperty="Opacity" From="1.0" To="0.0" Duration="0:0:2" AutoReverse="True" />
16 </Storyboard>
17 <Storyboard x:Name="myStoryboard3" Completed="Storyboard_Completed">
18 <DoubleAnimation x:Name="myDoubleAnimation3" Storyboard.TargetProperty="Opacity" From="1.0" To="0.0" Duration="0:0:2" AutoReverse="True" />
19 </Storyboard>
20 </StackPanel.Resources>
21 <Rectangle x:Name="MyAnimatedRectangle1" Margin="3" Width="90" Height="100" Fill="Blue" MouseLeftButtonDown="Start_Animation" Cursor="Hand" />
22 <Rectangle x:Name="MyAnimatedRectangle2" Margin="3" Width="90" Height="100" Fill="Blue" MouseLeftButtonDown="Start_Animation" Cursor="Hand" />
23 <Rectangle x:Name="MyAnimatedRectangle3" Margin="3" Width="90" Height="100" Fill="Blue" MouseLeftButtonDown="Start_Animation" Cursor="Hand" />
24 <Rectangle x:Name="MyAnimatedRectangle4" Margin="3" Width="90" Height="100" Fill="Blue" MouseLeftButtonDown="Start_Animation" Cursor="Hand" />
25 </StackPanel>
26
27</UserControl>
28
StackPanel中横向放了4个矩形，同时放置了三个完全相同的double型动画(用来让对象的透明度从1变到0，即渐渐淡去)，实现目的：4个矩形，3个动画，显示按照一一对应的默认原则，总会有一个矩形无法分配到动画，如何实现重用呢？看下面的
cs部分：
Code
1using System;
2using System.Windows.Controls;
3using System.Windows.Input;
4using System.Windows.Media.Animation;
5using System.Windows.Shapes;
6
7namespace AnimationControl
8{
9 public partial class Change2 : UserControl
10 {
11 public Change2()
12 {
13 InitializeComponent();
14 }
15
16 bool storyboard1Active = false;
17 bool storyboard2Active = false;
18 bool storyboard3Active = false;
19
20 private void Start_Animation(object sender, MouseEventArgs e)
21 {
22 //得到被点击的矩形对象引用
23 Rectangle myRect = (Rectangle)sender;
24
25 if (!storyboard1Active)
26 {
27 myStoryboard1.Stop();
28 myDoubleAnimation1.SetValue(Storyboard.TargetNameProperty, myRect.Name);
29 myStoryboard1.Begin();
30 storyboard1Active = true;
31 }
32 else if (!storyboard2Active)
33 {
34 myStoryboard2.Stop();
35 myDoubleAnimation2.SetValue(Storyboard.TargetNameProperty, myRect.Name);
36 myStoryboard2.Begin();
37 storyboard2Active = true;
38 }
39 else if (!storyboard3Active)
40 {
41 myStoryboard3.Stop();
42 myDoubleAnimation3.SetValue(Storyboard.TargetNameProperty, myRect.Name);
43 myStoryboard3.Begin();
44 storyboard3Active = true;
45 }
46 }
47
48 private void Storyboard_Completed(object sender, EventArgs e)
49 {
50 Storyboard myStoryboard = sender as Storyboard;
51 switch (myStoryboard.GetValue(NameProperty).ToString())
52 {
53 case "myStoryboard1": storyboard1Active = false; break;
54 case "myStoryboard2": storyboard2Active = false; break;
55 case "myStoryboard3": storyboard3Active = false; break;
56 }
57 }
58
59 }
60}
61
这里注意：定义了三个标识变量，用于标识每个动画是否正在播放中，如果播放完成后该变量为false，否则为true(即正在播放)，这个每个矩形上点击请求播放动画时，总是优先找到空闲（即处于播放状态）的动画，然后为该动画赋值TargetName属性并播放，同时播放途中把对应的标识变量改成true，以防止播放过程中被人修改TargetName值
也许有人会问了:如果没找到空闲的动画，不是没效果了？Yes，你猜对了，如果快速依次点击4个矩形，会发现最后一次点击没什么变化。这种情况就要用到下面提到的代码动态创建动画了
3。示例3 代码动态创建动画
理解起来很简单，代码创建动画对象，并让其播放。
xaml部分:
Code
1<UserControl x:Class="AnimationControl.Create"
2 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
5 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
6 mc:Ignorable="d"
7 >
8
9 <Canvas Name="LayoutRoot" Background="DarkOliveGreen" Width="400" Height="300">
10 <TextBlock Text="点击我将动态创建一段动画" MouseLeftButtonDown="TextBlock_MouseLeftButtonDown" Foreground="White" FontStretch="Normal" FontWeight="Bold" FontSize="18" TextAlignment="Center" Canvas.Left="100" Canvas.Top="130" Cursor="Hand" Opacity="0.5">
11
12 </TextBlock>
13 </Canvas>
14</UserControl>
15
一个几乎是空的Canvas，没啥特别的
再来看cs部分:
Code
1using System;
2using System.Windows;
3using System.Windows.Controls;
4using System.Windows.Media;
5using System.Windows.Media.Animation;
6using System.Windows.Shapes;
7
8namespace AnimationControl
9{
10 public partial class Create : UserControl
11 {
12 public Create()
13 {
14
15 InitializeComponent();
16
17 }
18
19 public void CreateAnimation()
20 {
21 //创建一个矩形
22 Rectangle myRectangle = new Rectangle();
23 myRectangle.Width = 50;
24 myRectangle.Height = 50;
25 myRectangle.Fill = new SolidColorBrush(Color.FromArgb(255, 255, 0, 0));
26
27 //把矩形加入到Canvas中
28 LayoutRoot.Children.Add(myRectangle);
29
30 //创建二个double型的动画，并设定播放时间为2秒
31 Duration duration = new Duration(TimeSpan.FromSeconds(2));
32 DoubleAnimation myDoubleAnimation1 = new DoubleAnimation();
33 DoubleAnimation myDoubleAnimation2 = new DoubleAnimation();
34
35 myDoubleAnimation1.Duration = duration;
36 myDoubleAnimation2.Duration = duration;
37
38 //创建故事版，并加入上面的二个double型动画
39 Storyboard sb = new Storyboard();
40 sb.Duration = duration;
41
42 sb.Children.Add(myDoubleAnimation1);
43 sb.Children.Add(myDoubleAnimation2);
44
45 //设置动画的Target目标值
46 Storyboard.SetTarget(myDoubleAnimation1, myRectangle);
47 Storyboard.SetTarget(myDoubleAnimation2, myRectangle);
48
49 //设置动画的变化属性
50 Storyboard.SetTargetProperty(myDoubleAnimation1, new PropertyPath("(Canvas.Left)"));
51 Storyboard.SetTargetProperty(myDoubleAnimation2, new PropertyPath("(Canvas.Top)"));
52
53 myDoubleAnimation1.To = 200;
54 myDoubleAnimation2.To = 200;
55
56 if (!LayoutRoot.Resources.Contains("unique_id"))
57 {
58 //将动画版加入Canvas资源,注意：这里的unique_id必须是资源中没有的唯一键
59 LayoutRoot.Resources.Add("unique_id", sb);
60 sb.Completed += new EventHandler(sb_Completed);
61
62 //播放
63 sb.Begin();
64 }
65 else
66 {
67 sb = null;
68 LayoutRoot.Children.Remove(myRectangle);
69 }
70
71
72
73 }
74
75 void sb_Completed(object sender, EventArgs e)
76 {
77 LayoutRoot.Resources.Remove("unique_id");//播放完成后，移除资源，否则再次点击时将报错
78 }
79
80 private void TextBlock_MouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
81 {
82 CreateAnimation();
83 }
84 }
85}
86
几乎所有关键的地方，都加了注释了应该能容易看明白
这里有一点要注意：创建动画的代码，必须放在构造函数中的InitializeComponent()之后调用，原因很简单，如果组件尚未初始化完毕，这时向根容器加入一些动态创建的元件当然会报错。
