[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。