控制Storyboard播放zz

<Grid Width="300" Height="460">
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>        
            <RowDefinition Height="60"/>
            <RowDefinition Height="100"/>
        </Grid.RowDefinitions>
        <Grid.Triggers>
            <EventTrigger SourceName="btnStart" RoutedEvent="Button.Click">
                <BeginStoryboard x:Name="myImageBStoryboard"  >
                    <Storyboard CurrentTimeInvalidated="Storyboard_CurrentTimeInvalidated">
                        <DoubleAnimation Storyboard.TargetName="myImageB" Storyboard.TargetProperty="Opacity" From="1" To="0" Duration="00:00:05">
                            
                        </DoubleAnimation>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
            <EventTrigger SourceName="btnPause" RoutedEvent="Button.Click">
                <PauseStoryboard BeginStoryboardName="myImageBStoryboard"></PauseStoryboard>
            </EventTrigger>
            <EventTrigger SourceName="btnResume" RoutedEvent="Button.Click">
                <ResumeStoryboard BeginStoryboardName="myImageBStoryboard"></ResumeStoryboard>
            </EventTrigger>
            <EventTrigger SourceName="btnStop" RoutedEvent="Button.Click">
                <StopStoryboard BeginStoryboardName="myImageBStoryboard"></StopStoryboard>
            </EventTrigger>
            <EventTrigger SourceName="btnMiddle" RoutedEvent="Button.Click">
                <SeekStoryboard BeginStoryboardName="myImageBStoryboard" Offset="00:00:02">                    
                </SeekStoryboard>
            </EventTrigger>
        </Grid.Triggers>
        <Grid Grid.Row="0" Grid.Column="0"  >
            <Image x:Name="myImageA" Source="Images/A.jpg"  Height="300" Width="300" Stretch="Fill"></Image>
            <Image x:Name="myImageB" Source="Images/B.jpg"   Height="300" Width="300"  Stretch="Fill" ></Image>
        </Grid>
        <StackPanel Grid.Row="1" Grid.Column="0" Orientation="Horizontal">            
            <Button x:Name="btnStart" Content="Start" Width="50" Height="40"  Margin="3" ></Button>
            <Button x:Name="btnPause" Content="Pause" Width="50" Height="40" Margin="3" ></Button>
            <Button x:Name="btnResume" Content="Resume" Width="50" Height="40" Margin="3" ></Button>
            <Button x:Name="btnStop" Content="Stop" Width="50" Height="40" Margin="3" ></Button>
            <Button x:Name="btnMiddle" Content="SeekToMiddle" Width="50" Height="40" Margin="3" ></Button>
        </StackPanel>
        <StackPanel Grid.Row="2" Grid.Column="0" Orientation="Vertical">
            <TextBlock x:Name="myTextBlock" FontSize="13" Foreground="Red"> </TextBlock>
            <ProgressBar x:Name="myProgressBar"  Height="35" Background="White" Width="300" >
                <ProgressBar.Foreground>
                    <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                        <GradientStop Color="#FF4DF22F" Offset="0.505" />
                        <GradientStop Color="#FFEFF5F1" Offset="1" />
                        <GradientStop Color="#FFF8F8F8" Offset="0.013" />
                    </LinearGradientBrush>
                </ProgressBar.Foreground>
            </ProgressBar>
        </StackPanel>
    </Grid>

public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Storyboard_CurrentTimeInvalidated(object sender, EventArgs e)
        {
            Clock storyboardClock = sender as Clock;
            if (storyboardClock.CurrentProgress != null)
            {
                myTextBlock.Text = storyboardClock.CurrentTime.ToString();
                myProgressBar.Value = (double)storyboardClock.CurrentProgress*100;(注意这儿storyboardClock.CurrentProgres值范围是0至1)
                System.Diagnostics.Debug.WriteLine(myProgressBar.Value);
            }
            else
            {
                myProgressBar.Value = 0;
                myTextBlock.Text = "Stopped";
            }
        }
    }