Issue Trying To Get Button Border to Animate on Click

I'm trying to animate the border of a button, but having trouble getting it to work. Here's the XAML I setup:

<Button x:Name="Btn">
    &l开发者_JAVA百科t;Button.Triggers>
        <EventTrigger RoutedEvent="Button.Click">
            <BeginStoryboard>
                <Storyboard Duration="100" AutoReverse="True"
                            Storyboard.TargetName="Btn"                                     
                            Storyboard.TargetProperty="BorderBrush">
                    <ColorAnimation To="Yellow" />
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </Button.Triggers>
</Button>

I'm getting this error:

Failed to assign to property 'System.Windows.EventTrigger.RoutedEvent'. [Line: 17 Position: 30]

Any idea why? Total noob at this. I'm using Silverlight 4.

---

Silverlight only supports the Loaded event in an event trigger. For this sort of thing you need to be looking into Visual State Manager.

The Button already supports a Visual State called "Pressed". However in order to change the buttons visual behaviour you need to first copy its default template and place it in a static resource.

You can get a copy of the default style used for button here. Lets assume you give this a x:Key of "MyButtonStyle".

You would add your ColorAnimation to the existing Storyboard for the "Pressed" VisualState.

Then your button xaml should be:

<Button Style="{StaticResource MyButtonStyle}" Content="Click Me" />