在前面的Silverlight入门系列文章中穿插讲了一些MVVM模式系列文章，MVVM模式貌似简单，其实要把界面逻辑抽象出来还是很不容易，像《TreeView真正实现MVVM模式和Expanded发生时异步动态加载子节点(WCFRiaService)》就不是这么简单，有的童鞋像feiyang还要实现Treeview的展开状态持久化和自动恢复，配合MVVM实现不容易。所以，MVVM的核心概念理解不难，在具体使用上则问题多多。今天要讲的话题就是一个MVVM使用上的具体问题: Silverlight中的Storyboard动画是否可以在ViewModel中来控制？

 

为什么想在ViewModel中控制Storyboard?

假设我的业务逻辑在ViewModel中，业务操作好了保存Save成功了就需要启动一个动画：Stobyboard.begin()。而这个动画在视图中，怎么去控制它？这个需求很普遍吧。确实很普遍，但实现就不那么简单了，不像下面这样的Storyboard启动那么简单：

   1: <Image x:Name="myImage" 
   2:   Source="http://www.silverlightinaction.com/man.png">
   3:   <Image.Triggers>
   4:     <EventTrigger RoutedEvent="Image.Loaded">
   5:       <BeginStoryboard> 
   6:         <Storyboard x:Name="myStoryboard"> 
   7:           <DoubleAnimation Duration="0:0:2"
   8:                            Storyboard.TargetName="myImage"
   9:                            Storyboard.TargetProperty="Opacity"
  10:                            From="0" To="1" />
  11:         </Storyboard>
  12:       </BeginStoryboard>
  13:     </EventTrigger>
  14:   </Image.Triggers>
  15: </Image>

 

解决方法一：ViewModel中用事件Event通知View启动Storyboard动画

ViewModel是对界面逻辑、业务逻辑、和模型数据的封装和抽象，ViewModel不依赖于具体的View视图，所以ViewModel根本不知道具体的某个Storyboard，怎么去启动这个动画呢? 解决问题思路有好多：第一种方法就是很自然的想到在ViewModel中用事件Event通知View启动动画。具体做法是：在ViewModel中添加一个事件Event，当业务操作好了保存Save成功了用这个事件通知View，这样View在Event的处理函数里面打开动画即可。

ViewModel代码：

   1: public class YourViewModel 
   2: { 
   3:     public delegate void YourEventHandler(object sender, EventArgs e); 
   4:     public event YourEventHandler YourEvent; 
   5:     protected void OnYourEvent(EventArgs e) { 
   6:         if (YourEvent != null) YourEvent(this, e); 
   7:     } 
   8:     
   9:     //当业务操作好了保存Save成功了触发这个事件
  10:     //OnYourEvent(new EventArgs(a));
  11: }

在Xaml.cs写code behind代码：

   1: var vm = new YourViewModel();
   2: vm.YourEvent += (s,e) => 
   3: {
   4:    var story = Resources["YourTransition"] as Storyboard;
   5:    story.Begin();
   6: }; 
   7: this.DataContext = vm;

 

解决方法二：ViewModel属性和View绑定并用Trigger

大家知道，ViewModel的属性可以和View绑定，当属性变化的时候用NotifyPropertyChanged自动通知View。按照这个思路，我们只要在ViewModel加一个属性，当业务操作好了保存Save成功了就改变这个属性的值，然后就会自动通知View，在View中加个Trigger，当绑定的值变化的时候就触发启动动画。

假设ViewModel属性为bool PopupSideShow. 在视图中：

   1: xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

Storyboard定义在Resource中：（此处Storyboard没实际意义仅为演示）

   1: <UserControl.Resources>
   2:     <Storyboard x:Name="popupSideShowStory">
   3:         <DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Height" From="0" To="{Binding _PopupSideHeight}" Duration="0:0:1" />
   4:         <DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Width" From="0" To="{Binding _PopupSideWidth}" Duration="0:0:1" />
   5:     </Storyboard>
   6:     <Storyboard x:Name="popupSideHideStory">
   7:         <DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Height" From="{Binding _PopupSideHeight}" To="0" Duration="0:0:.8" />
   8:         <DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Width" From="{Binding _PopupSideWidth}" To="0" Duration="0:0:.8" />
   9:     </Storyboard>
  10: </UserControl.Resources>

在View视图中绑定ViewModel属性为bool PopupSideShow，并用Trigger实现当绑定的值PopupSideShow变化的时候就触发启动动画：

   1: <Grid x:Name="PopUpDisplaySide"  Background="White">
   2:    <i:Interaction.Triggers>
   3:       <ei:DataTrigger Binding="{Binding PopupSideShow}" Value="true">
   4:          <ei:ControlStoryboardAction Storyboard="{StaticResource popupSideShowStory}"/>
   5:       </ei:DataTrigger>
   6:       <ei:DataTrigger Binding="{Binding PopupSideShow}" Value="false">
   7:          <ei:ControlStoryboardAction Storyboard="{StaticResource popupSideHideStory}"/>
   8:       </ei:DataTrigger>
   9:    </i:Interaction.Triggers>
  10:    <StackPanel Orientation="Vertical">
  11:       <TextBlock Text="{Binding _PopupTitle}" FontSize="16" />
  12:    </StackPanel>
  13: </Grid>

 

解决方法三：加一个中间人管理Storyboard从而既实现ViewModel和View解耦，又能在ViewModel控制StoryboardViewModel属性和View

既然我们想在ViewModel里面控制Storyboard，而ViewModel又不能依赖具体的View，所以我们可以加个中间人把Storyboard抽象出来，这样既能实现ViewModel和View解耦，又能在ViewModel通过中间人控制Storyboard。这个思路我想也是很自然的。但怎么实现呢？首先这个中间人要和View发生联系必须要能在Xaml里面绑定，所以我们要实现DependencyProperty。

我们首先加一个StoryboardManager:

   1: using System;
   2: using System.Windows;
   3: using System.Windows.Media.Animation;
   4: using System.Collections.Generic;
   5:  
   6: namespace TestVMAnimation
   7: {
   8:     public class StoryboardManager
   9:     {
  10:         public static DependencyProperty IDProperty =
  11:             DependencyProperty.RegisterAttached("ID", typeof(string), typeof(StoryboardManager),
  12:                     new PropertyMetadata(null, IdChanged));
  13:         
  14:         static readonly Dictionary<string, Storyboard> Storyboards = new Dictionary<string, Storyboard>();
  15:  
  16:         public delegate void Callback(object state);
  17:  
  18:         /// <summary>
  19:         /// IDs the changed.
  20:         /// </summary>
  21:         /// <param name="obj">The obj.</param>
  22:         /// <param name="e">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>
  23:         private static void IdChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e) 
  24:         { 
  25:             var sb = obj as Storyboard; 
  26:             if (sb == null)            
  27:                 return; 
  28:             
  29:             var key = e.NewValue as string; 
  30:             if (Storyboards.ContainsKey(key))            
  31:                 Storyboards[key] = sb; 
  32:             else            
  33:                 Storyboards.Add(key, sb); 
  34:         }
  35:  
  36:         /// <summary>
  37:         /// Plays the storyboard.
  38:         /// </summary>
  39:         /// <param name="id">The id.</param>
  40:         /// <param name="callback">The callback.</param>
  41:         /// <param name="state">The state.</param>
  42:         public static void PlayStoryboard(string id, Callback callback, object state) 
  43:         { 
  44:             if (!Storyboards.ContainsKey(id)) 
  45:             { 
  46:                 callback(state); 
  47:                 return; 
  48:             } 
  49:             Storyboard sb = Storyboards[id]; 
  50:             EventHandler handler = null;
  51:             EventHandler handlertemp = handler;
  52:             handler = delegate { sb.Completed -= handlertemp; callback(state); }; 
  53:             sb.Completed += handler; 
  54:             sb.Begin(); 
  55:         }
  56:  
  57:         /// <summary>
  58:         /// Sets the ID.
  59:         /// </summary>
  60:         /// <param name="obj">The obj.</param>
  61:         /// <param name="id">The id.</param>
  62:         public static void SetID(DependencyObject obj, string id) 
  63:         { 
  64:             obj.SetValue(IDProperty, id); 
  65:         }
  66:  
  67:         /// <summary>
  68:         /// Gets the ID.
  69:         /// </summary>
  70:         /// <param name="obj">The obj.</param>
  71:         /// <returns></returns>
  72:         public static string GetID(DependencyObject obj) 
  73:         { 
  74:             return obj.GetValue(IDProperty) as string; 
  75:         }
  76:     }
  77:     
  78: }

有了DependencyProperty就可以在Xaml里面绑定了，注意下面的StoryboardManager.ID：

   1: <UserControl.Resources>
   2:     <Storyboard x:Key="YourStoryboardResourceKey" 
   3:              StoryboardManager:StoryboardManager.ID="YourAnimation">
   4:         <DoubleAnimation By="360" Duration="0:0:1" Storyboard.TargetName="btn1"
   5:                          Storyboard.TargetProperty="Angle" />
   6:     </Storyboard>
   7: </UserControl.Resources>

在ViewModel里面控制Storyboard很简单，下面这个例子是通过Command调用的，你当然也可以不通过Command直接调用Storyboard，像本文的例子，可以在ViewModel的业务逻辑里面当业务操作好了保存Save成功了启动Storyboard动画。

   1: public class YourViewModel
   2: {
   3:     public ICommand PlayStoryboardCommand   {  get; private set;  }
   4:     
   5:     public YourViewModel()
   6:     {
   7:         PlayStoryboardCommand = new DelegateCommand(
   8:             () => {
   9:                         StoryboardManager.PlayStoryboard("YourAnimation", (o) => { }, null);
  10:         });
  11:     }
  12:  
  13:     
  14: }

 

解决方法四：不要在ViewModel里面控制Storyboard，把Transition封装在控件中

用MVVM模式的出发点之一就是分离关注点（Separation of concerns). View负责什么？UI Layout, structure, appearance，animation, 那View的CodeBehind（Xaml.cs）可以有什么？View的Code Behind可以有Initialize Component, 可以有Xaml里面表示不了的视觉行为，比如复杂动画控制（带callback，completed事件那种）。还可以是视觉元素的控制。总之，只要这些代码是View该负责的，是高内聚的，是不想被重用的，是不能被测试的，那你就搁在code behind好了。绝对应该避免业务逻辑在里面哦。某位大神说过，“解决问题的最好办法是think different，说不定问题本身就不是个问题”。是的，你想在ViewModel里面控制Storyboard，这本身是不是有问题? 想想我们的动画一般在什么时候发生？真的是业务逻辑完成了发生吗？真的和业务逻辑相关吗？不！动画其实是和VisualElement的VisualState相关。也就是说，我们往往是在某个panel显示/隐藏/打开/关闭的时候有个淡入淡出、推箱子、跳跃、或者x/y/z/3D旋转的效果（不要告诉我是显示/隐藏panel本身，这个可以和ViewModel的属性绑定的，不是动画）。说白了就是一个transition，从一个VisualState到另一个VisualState而已。好了，想清楚了，问题就没有了。也就是说，你无须在ViewModel里面控制Storyboard，只要在View里面定义好VisualState就可以了，封装在控件行为中，把VisualState动画写在控件的模板中，有关怎么封装Silverlight控件这儿就不多说了，下回有空再说。具体做法可以参考MSDN这个页面，里面就有button的VisualState切换动画，比如MouseOver等:

   1: <Style TargetType="Button">
   2:       <Setter Property="Background" Value="#FF1F3B53"/>
   3:       <Setter Property="Foreground" Value="#FF000000"/>
   4:       <Setter Property="Padding" Value="3"/>
   5:       <Setter Property="BorderThickness" Value="1"/>
   6:       <Setter Property="BorderBrush">
   7:           <Setter.Value>
   8:               <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
   9:                   <GradientStop Color="#FFA3AEB9" Offset="0"/>
  10:                   <GradientStop Color="#FF8399A9" Offset="0.375"/>
  11:                   <GradientStop Color="#FF718597" Offset="0.375"/>
  12:                   <GradientStop Color="#FF617584" Offset="1"/>
  13:               </LinearGradientBrush>
  14:           </Setter.Value>
  15:       </Setter>
  16:       <Setter Property="Template">
  17:           <Setter.Value>
  18:               <ControlTemplate TargetType="Button">
  19:                   <Grid>
  20:                       <vsm:VisualStateManager.VisualStateGroups>
  21:                           <vsm:VisualStateGroup x:Name="CommonStates">
  22:                               <vsm:VisualState x:Name="Normal"/>
  23:                               <vsm:VisualState x:Name="MouseOver">
  24:                                   <Storyboard>
  25:                                       <DoubleAnimation Duration="0" Storyboard.TargetName="BackgroundAnimation" Storyboard.TargetProperty="Opacity" To="1"/>
  26:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" To="#F2FFFFFF"/>
  27:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" To="#CCFFFFFF"/>
  28:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" To="#7FFFFFFF"/>
  29:                                   </Storyboard>
  30:                               </vsm:VisualState>
  31:                               <vsm:VisualState x:Name="Pressed">
  32:                                   <Storyboard>
  33:                                       <ColorAnimation Duration="0" Storyboard.TargetName="Background" Storyboard.TargetProperty="(Border.Background).(SolidColorBrush.Color)" To="#FF6DBDD1"/>
  34:                                       <DoubleAnimation Duration="0" Storyboard.TargetName="BackgroundAnimation" Storyboard.TargetProperty="Opacity" To="1"/>
  35:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)" To="#D8FFFFFF"/>
  36:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" To="#C6FFFFFF"/>
  37:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" To="#8CFFFFFF"/>
  38:                                       <ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" To="#3FFFFFFF"/>
  39:                                   </Storyboard>
  40:                               </vsm:VisualState>
  41:                               <vsm:VisualState x:Name="Disabled">
  42:                                   <Storyboard>
  43:                                       <DoubleAnimation Duration="0" Storyboard.TargetName="DisabledVisualElement" Storyboard.TargetProperty="Opacity" To=".55"/>
  44:                                   </Storyboard>
  45:                               </vsm:VisualState>
  46:                           </vsm:VisualStateGroup>
  47:                           <vsm:VisualStateGroup x:Name="FocusStates">
  48:                               <vsm:VisualState x:Name="Focused">
  49:                                   <Storyboard>
  50:                                       <DoubleAnimation Duration="0" Storyboard.TargetName="FocusVisualElement" Storyboard.TargetProperty="Opacity" To="1"/>
  51:                                   </Storyboard>
  52:                               </vsm:VisualState>
  53:                               <vsm:VisualState x:Name="Unfocused" />
  54:                           </vsm:VisualStateGroup>
  55:                       </vsm:VisualStateManager.VisualStateGroups>
  56:                       <Border x:Name="Background" CornerRadius="3" Background="White" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}">
  57:                           <Grid Background="{TemplateBinding Background}"  Margin="1">
  58:                               <Border Opacity="0"  x:Name="BackgroundAnimation" Background="#FF448DCA" />
  59:                               <Rectangle x:Name="BackgroundGradient" >
  60:                                   <Rectangle.Fill>
  61:                                       <LinearGradientBrush StartPoint=".7,0" EndPoint=".7,1">
  62:                                           <GradientStop Color="#FFFFFFFF" Offset="0" />
  63:                                           <GradientStop Color="#F9FFFFFF" Offset="0.375" />
  64:                                           <GradientStop Color="#E5FFFFFF" Offset="0.625" />
  65:                                           <GradientStop Color="#C6FFFFFF" Offset="1" />
  66:                                       </LinearGradientBrush>
  67:                                   </Rectangle.Fill>
  68:                               </Rectangle>
  69:                           </Grid>
  70:                       </Border>
  71:                       <ContentPresenter
  72:                               x:Name="contentPresenter"
  73:                               Content="{TemplateBinding Content}"
  74:                               ContentTemplate="{TemplateBinding ContentTemplate}"
  75:                               VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
  76:                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
  77:                               Margin="{TemplateBinding Padding}"/>
  78:                       <Rectangle x:Name="DisabledVisualElement" RadiusX="3" RadiusY="3" Fill="#FFFFFFFF" Opacity="0" IsHitTestVisible="false" />
  79:                       <Rectangle x:Name="FocusVisualElement" RadiusX="2" RadiusY="2" Margin="1" Stroke="#FF6DBDD1" StrokeThickness="1" Opacity="0" IsHitTestVisible="false" />
  80:                   </Grid>
  81:               </ControlTemplate>
  82:           </Setter.Value>
  83:       </Setter>
  84:   </Style>

 

解决方法五：把Storyboard作为ViewModel的一个属性给View来绑定（糟糕的主意）

也许有人会想到这个主意：在ViewModel中加个Storyboard类型的属性，给view绑定传进去，这样在ViewModel的业务逻辑中当业务操作好了保存Save成功了就可以直接调用自己的Storyboard.begin()，岂不爽哉？我想说这是个糟糕的主意，为什么？不要把业务逻辑无关的纯UI的元素混到viewModel里面，难道要抽象依赖于具体？

 

解决方法六：用VisualStateManager，在ViewModel用事件通知View（仅供参考）

用VisualStateManager的方法（Event同方法一的事件），在视图收到事件通知以后，调用StateManager启动动画而已。在xaml.cs中：

   1:  
   2: VisualStateManager.GoToState(this, "YourState1", true);
   3: 
在Xaml中把动画不要定义在Resource中，而是定义为几个VisualState: 
   1: xmlns:ic="clr-namespace:Microsoft.Expression.Interactivity.Core;assembly=Microsoft.Expression.Interactions"
   2:  
   3: <Grid x:Name="LayoutRoot">
   4:         <VisualStateManager.CustomVisualStateManager>
   5:             <ic:ExtendedVisualStateManager/>
   6:         </VisualStateManager.CustomVisualStateManager>
   7:         <VisualStateManager.VisualStateGroups>
   8:             <VisualStateGroup x:Name="EditViewGroup" ic:ExtendedVisualStateManager.UseFluidLayout="True">
   9:                 <VisualStateGroup.Transitions>
  10:                     <VisualTransition GeneratedDuration="00:00:00.2500000"/>
  11:                 </VisualStateGroup.Transitions>
  12:                 <VisualState x:Name="YourState1">
  13:                     <Storyboard>
  14:                         <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(FrameworkElement.Margin)">
  15:                             <DiscreteObjectKeyFrame KeyTime="00:00:00">
  16:                                 <DiscreteObjectKeyFrame.Value>
  17:                                     <Thickness>0,0,0,-101</Thickness>
  18:                                 </DiscreteObjectKeyFrame.Value>
  19:                             </DiscreteObjectKeyFrame>
  20:                         </ObjectAnimationUsingKeyFrames>
  21:                     </Storyboard>
  22:                 </VisualState>
  23:                 <VisualState x:Name="YourState2">
  24:                     <Storyboard>
  25:                         <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[3].(TranslateTransform.X)">
  26:                             <EasingDoubleKeyFrame KeyTime="00:00:00" Value="3"/>
  27:                         </DoubleAnimationUsingKeyFrames>
  28:                         <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[3].(TranslateTransform.Y)">
  29:                             <EasingDoubleKeyFrame KeyTime="00:00:00" Value="-101"/>
  30:                         </DoubleAnimationUsingKeyFrames>
  31:                         <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(FrameworkElement.Margin)">
  32:                             <DiscreteObjectKeyFrame KeyTime="00:00:00">
  33:                                 <DiscreteObjectKeyFrame.Value>
  34:                                     <Thickness>-4,0,0,-101</Thickness>
  35:                                 </DiscreteObjectKeyFrame.Value>
  36:                             </DiscreteObjectKeyFrame>
  37:                         </ObjectAnimationUsingKeyFrames>
  38:                     </Storyboard>
  39:                 </VisualState>
  40:             </VisualStateGroup>
  41:         </VisualStateManager.VisualStateGroups>
  42: </Grid>

 

总结

以上几种方法个人觉得第二种最好，第三种次之，第四种也不错但是比较费时间。我们遇到问题不仅仅是思考问题，解决问题，还要发散思维想想多重解决方案并选择最优最简单的方案；如果当初是赶时间，那后续就需要重构来寻求最优解决方案。这种重构是有意义的。就像我在前一篇中如何在Silverlight页面间传递复杂对象，也给出了5种解决方法，选择最优的一种，好的攻城师应当多钻研，多分享，多接受批评和自我批评，这样才能进步的快一些。

 

继续阅读 – Silverlight入门MVVM系列

 

继续阅读 - Silverlight入门系列

 

作者: Mainz 发表于 2011-08-25 22:27 原文链接

关键字 silverlight入门系列,使用mvvm模式,想在viewmodel中控制storyboard动画？
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