WPF/Silverlight:如何在MVVM中使用DataTrigger故事板动画？

<Window x:Class="MyApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyApp"
        Title="MyApp" Height="450" Width="800">
    <Window.DataContext>
        <local:MyViewModel />
    </Window.DataContext>
    <Grid>
        <Rectangle Width="100" Height="100" Fill="Red">
            <Rectangle.Style>
                <Style TargetType="Rectangle">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding IsAnimating}" Value="True">
                            <DataTrigger.EnterActions>
                                <BeginStoryboard>
                                    <Storyboard>
                                        <DoubleAnimation From="0" To="360" Duration="0:0:2" RepeatBehavior="Forever" Storyboard.TargetProperty="Angle" />
                                    </Storyboard>
                                </BeginStoryboard>
                            </DataTrigger.EnterActions>
                            <DataTrigger.ExitActions>
                                <StopStoryboard BeginStoryboardName="StoryboardName" />
                            </DataTrigger.ExitActions>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </Rectangle.Style>
        </Rectangle>
    </Grid>
</Window>