How Do I Make aTextBlock Blink Only When a Dependency Property of the ViewModel Has a Certain Value?
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I have a View Model object that has a depednency property called `IsSearching`; it is a `bool`.  My form has a `TextBlock` control that is used to display the number of matching rows.  The property that is bound to the `TextBlock's ` `Text` property is an  `int?` type.  At the start of the search, the property is set to `null`.  The converter in the binding displays this as "--".  

I want the "--" string to flash while the `IsSearching` property is `true`, and I don't want it flash when it is `false`.  Here's what I have so far:

The `StoryBoard`:

    <Storyboard x:Key="FlashTextBlockText">
        <ObjectAnimationUsingKeyFrames RepeatBehavior="Forever" Storyboard.TargetProperty="(UIElement.Visibility)">
            <DiscreteObjectKeyFrame KeyTime="0:0:0.5" Value="{x:Static Visibility.Hidden}" />
            <DiscreteObjectKeyFrame KeyTime="0:0:1"   Value="{x:Static Visibility.Visible}" />
        </ObjectAnimationUsingKeyFrames>
    </Storyboard>

A named `Style` for `TextBlocks` only:

    <Style BasedOn="{StaticResource {x:Type TextBlock}}" x:Key="FlashBlockText" TargetType="TextBlock">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=IsSearching}" Value="True">
                <DataTrigger.EnterActions>
                    <BeginStoryboard Storyboard="{StaticResource FlashTextBlockText}" />
                </DataTrigger.EnterActions>
            </DataTrigger>
        </Style.Triggers>
    </Style>

The `IsSearching` property is initially `false`.  When the user clicks on the Search `Button`, it is set to true and the flashing begins.  But it doesn't stop flashing.

How do I get the `StoryBoard` to stop when `IsSearching` is set back to `false`?

Tony