[Silverlight入门系列]使用MVVM模式(9): 想在ViewModel中控制Storyboard动画？

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：

<Image x:Name="myImage"

Source="http://www.silverlightinaction.com/man.png">

<Image.Triggers>

<EventTrigger RoutedEvent="Image.Loaded">

<BeginStoryboard>

<Storyboard x:Name="myStoryboard">

<DoubleAnimation Duration="0:0:2"

Storyboard.TargetName="myImage"

Storyboard.TargetProperty="Opacity"

From="0" To="1" />

</Storyboard>

</BeginStoryboard>

</EventTrigger>

</Image.Triggers>

</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：

public class YourViewModel

{

public delegate void YourEventHandler(object sender, EventArgs e);

public event YourEventHandler YourEvent;

protected void OnYourEvent(EventArgs e){

if (YourEvent != null) YourEvent(this, e);

}

//当业务操作好了保存Save成功了触发这个事件

//OnYourEvent(new EventArgs(a));

}

在Xaml.cs写code behind代码：

var vm = new YourViewModel();

vm.YourEvent += (s,e) =>

{

var story = Resources["YourTransition"] as Storyboard;

story.Begin();

};

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：

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

xmlns:ei=http://schemas.microsoft.com/expression/2010/interactions

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

<UserControl.Resources>

<Storyboard x:Name="popupSideShowStory">

<DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Height" From="0" To="{Binding _PopupSideHeight}" Duration="0:0:1" />

<DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Width" From="0" To="{Binding _PopupSideWidth}" Duration="0:0:1" />

</Storyboard>

<Storyboard x:Name="popupSideHideStory">

<DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Height" From="{Binding _PopupSideHeight}" To="0" Duration="0:0:.8" />

<DoubleAnimation Storyboard.TargetName="PopUpDisplaySide" Storyboard.TargetProperty="Width" From="{Binding _PopupSideWidth}" To="0" Duration="0:0:.8" />

</Storyboard>

</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：

<Grid x:Name="PopUpDisplaySide"Background="White">

<i:Interaction.Triggers>

<ei:DataTrigger Binding="{Binding PopupSideShow}" Value="true">

<ei:ControlStoryboardAction Storyboard="{StaticResource popupSideShowStory}"/>

</ei:DataTrigger>

<ei:DataTrigger Binding="{Binding PopupSideShow}" Value="false">

<ei:ControlStoryboardAction Storyboard="{StaticResource popupSideHideStory}"/>

</ei:DataTrigger>

</i:Interaction.Triggers>

<StackPanel Orientation="Vertical">

<TextBlock Text="{Binding _PopupTitle}" FontSize="16" />

</StackPanel>

</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:

using System;

using System.Windows;

using System.Windows.Media.Animation;

using System.Collections.Generic;

namespace TestVMAnimation

{

public class StoryboardManager

{

public static DependencyProperty IDProperty =

 DependencyProperty.RegisterAttached("ID", typeof(string), typeof(StoryboardManager),

 new PropertyMetadata(null, IdChanged));

static readonly Dictionary<string, Storyboard> Storyboards = new Dictionary<string, Storyboard>();

public delegate void Callback(object state);

/// <summary>

/// IDs the changed.

/// </summary>

/// <param name="obj">The obj.</param>

/// <param name="e">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>

private static void IdChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e) 

{

 var sb = obj as Storyboard; 

 if (sb == null)

return; 

 var key = e.NewValue as string; 

 if (Storyboards.ContainsKey(key))

Storyboards[key] = sb; 

 else

Storyboards.Add(key, sb); 

}

/// <summary>

/// Plays the storyboard.

/// </summary>

/// <param name="id">The id.</param>

/// <param name="callback">The callback.</param>

/// <param name="state">The state.</param>

public static void PlayStoryboard(string id, Callback callback, object state) 

{

 if (!Storyboards.ContainsKey(id)) 

{

callback(state); 

return; 

}

 Storyboard sb = Storyboards[id]; 

 EventHandler handler = null;

 EventHandler handlertemp = handler;

 handler = delegate{sb.Completed -= handlertemp; callback(state);};

 sb.Completed += handler; 

 sb.Begin(); 

}

/// <summary>

/// Sets the ID.

/// </summary>

/// <param name="obj">The obj.</param>

/// <param name="id">The id.</param>

public static void SetID(DependencyObject obj, string id) 

{

 obj.SetValue(IDProperty, id); 

}

/// <summary>

/// Gets the ID.

/// </summary>

/// <param name="obj">The obj.</param>

/// <returns></returns>

public static string GetID(DependencyObject obj) 

{

 return obj.GetValue(IDProperty) as string; 

}

}

}

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

<UserControl.Resources>

<Storyboard x:Key="YourStoryboardResourceKey" 

StoryboardManager:StoryboardManager.ID="YourAnimation">

<DoubleAnimation By="360" Duration="0:0:1" Storyboard.TargetName="btn1"

 Storyboard.TargetProperty="Angle" />

</Storyboard>

</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。

public class YourViewModel

{

public ICommand PlayStoryboardCommand{ get; private set;}

public YourViewModel()

{

PlayStoryboardCommand = new DelegateCommand(

 () =>{

StoryboardManager.PlayStoryboard("YourAnimation", (o) =>{}, null);

});

}

}

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:

<Style TargetType="Button">

<Setter Property="Background" Value="#FF1F3B53"/>

<Setter Property="Foreground" Value="#FF000000"/>

<Setter Property="Padding" Value="3"/>

<Setter Property="BorderThickness" Value="1"/>

<Setter Property="BorderBrush">

 <Setter.Value>

<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">

<GradientStop Color="#FFA3AEB9" Offset="0"/>

<GradientStop Color="#FF8399A9" Offset="0.375"/>

<GradientStop Color="#FF718597" Offset="0.375"/>

<GradientStop Color="#FF617584" Offset="1"/>

</LinearGradientBrush>

 </Setter.Value>

</Setter>

<Setter Property="Template">

 <Setter.Value>

<ControlTemplate TargetType="Button">

<Grid>

 <vsm:VisualStateManager.VisualStateGroups>

<vsm:VisualStateGroup x:Name="CommonStates">

 <vsm:VisualState x:Name="Normal"/>

 <vsm:VisualState x:Name="MouseOver">

<Storyboard>

<DoubleAnimation Duration="0" Storyboard.TargetName="BackgroundAnimation" Storyboard.TargetProperty="Opacity" To="1"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" To="#F2FFFFFF"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" To="#CCFFFFFF"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" To="#7FFFFFFF"/>

 </Storyboard>

 </vsm:VisualState>

 <vsm:VisualState x:Name="Pressed">

<Storyboard>

<ColorAnimation Duration="0" Storyboard.TargetName="Background" Storyboard.TargetProperty="(Border.Background).(SolidColorBrush.Color)" To="#FF6DBDD1"/>

<DoubleAnimation Duration="0" Storyboard.TargetName="BackgroundAnimation" Storyboard.TargetProperty="Opacity" To="1"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)" To="#D8FFFFFF"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" To="#C6FFFFFF"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" To="#8CFFFFFF"/>

<ColorAnimation Duration="0" Storyboard.TargetName="BackgroundGradient" Storyboard.TargetProperty="(Rectangle.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" To="#3FFFFFFF"/>

 </Storyboard>

 </vsm:VisualState>

 <vsm:VisualState x:Name="Disabled">

<Storyboard>

<DoubleAnimation Duration="0" Storyboard.TargetName="DisabledVisualElement" Storyboard.TargetProperty="Opacity" To=".55"/>

 </Storyboard>

 </vsm:VisualState>

</vsm:VisualStateGroup>

<vsm:VisualStateGroup x:Name="FocusStates">

 <vsm:VisualState x:Name="Focused">

<Storyboard>

<DoubleAnimation Duration="0" Storyboard.TargetName="FocusVisualElement" Storyboard.TargetProperty="Opacity" To="1"/>

 </Storyboard>

 </vsm:VisualState>

 <vsm:VisualState x:Name="Unfocused" />

</vsm:VisualStateGroup>

 </vsm:VisualStateManager.VisualStateGroups>

 <Border x:Name="Background" CornerRadius="3" Background="White" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}">

<Grid Background="{TemplateBinding Background}"Margin="1">

 <Border Opacity="0"x:Name="BackgroundAnimation" Background="#FF448DCA" />

 <Rectangle x:Name="BackgroundGradient" >

<Rectangle.Fill>

<LinearGradientBrush StartPoint=".7,0" EndPoint=".7,1">

 <GradientStop Color="#FFFFFFFF" Offset="0" />

 <GradientStop Color="#F9FFFFFF" Offset="0.375" />

 <GradientStop Color="#E5FFFFFF" Offset="0.625" />

 <GradientStop Color="#C6FFFFFF" Offset="1" />

</LinearGradientBrush>

</Rectangle.Fill>

 </Rectangle>

</Grid>

 </Border>

 <ContentPresenter

 x:Name="contentPresenter"

 Content="{TemplateBinding Content}"

 ContentTemplate="{TemplateBinding ContentTemplate}"

 VerticalAlignment="{TemplateBinding VerticalContentAlignment}"

 HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"

 Margin="{TemplateBinding Padding}"/>

 <Rectangle x:Name="DisabledVisualElement" RadiusX="3" RadiusY="3" Fill="#FFFFFFFF" Opacity="0" IsHitTestVisible="false" />

 <Rectangle x:Name="FocusVisualElement" RadiusX="2" RadiusY="2" Margin="1" Stroke="#FF6DBDD1" StrokeThickness="1" Opacity="0" IsHitTestVisible="false" />

</Grid>

</ControlTemplate>

 </Setter.Value>

</Setter>

 </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：

VisualStateManager.GoToState(this, "YourState1", true);

在Xaml中把动画不要定义在Resource中，而是定义为几个VisualState:

xmlns:ic="clr-namespace:Microsoft.Expression.Interactivity.Core;assembly=Microsoft.Expression.Interactions"

<Grid x:Name="LayoutRoot">

<VisualStateManager.CustomVisualStateManager>

 <ic:ExtendedVisualStateManager/>

</VisualStateManager.CustomVisualStateManager>

<VisualStateManager.VisualStateGroups>

 <VisualStateGroup x:Name="EditViewGroup" ic:ExtendedVisualStateManager.UseFluidLayout="True">

<VisualStateGroup.Transitions>

 <VisualTransition GeneratedDuration="00:00:00.2500000"/>

</VisualStateGroup.Transitions>

<VisualState x:Name="YourState1">

 <Storyboard>

<ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(FrameworkElement.Margin)">

<DiscreteObjectKeyFrame KeyTime="00:00:00">

 <DiscreteObjectKeyFrame.Value>

<Thickness>0,0,0,-101</Thickness>

 </DiscreteObjectKeyFrame.Value>

</DiscreteObjectKeyFrame>

</ObjectAnimationUsingKeyFrames>

</Storyboard>

</VisualState>

<VisualState x:Name="YourState2">

 <Storyboard>

<DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[3].(TranslateTransform.X)">

<EasingDoubleKeyFrame KeyTime="00:00:00" Value="3"/>

</DoubleAnimationUsingKeyFrames>

<DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[3].(TranslateTransform.Y)">

<EasingDoubleKeyFrame KeyTime="00:00:00" Value="-101"/>

</DoubleAnimationUsingKeyFrames>

<ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="GridFlyout" Storyboard.TargetProperty="(FrameworkElement.Margin)">

<DiscreteObjectKeyFrame KeyTime="00:00:00">

 <DiscreteObjectKeyFrame.Value>

<Thickness>-4,0,0,-101</Thickness>

 </DiscreteObjectKeyFrame.Value>

</DiscreteObjectKeyFrame>

</ObjectAnimationUsingKeyFrames>

</Storyboard>

</VisualState>

 </VisualStateGroup>

</VisualStateManager.VisualStateGroups>

</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。