WPF and AutoRedraw

I have a custom WPF Line and its style. UserControl Resources:

    <!-- Framework properties to update -->
    <SolidColorBrush x:Key="MyLineBrush" Color="LightGreen" />
    <sys:Double x:Key="MyLineStrokeThickness">1</sys:Double>

    <!-- Custom property to update -->
    <sys:Boolean x:Key="MyLineIsArrowUsed">false</sys:Boolean>


    <Style TargetType="local:MyLine" x:Key="MyLineStyleKey">

        <!-- AutoUpdates the control -->
        <Setter Property="Fill" 
                Value="{DynamicResource MyLineBrush}"/>
        <Setter Property="StrokeThickness" 
                Value="{DynamicResource MyLineStrokeThickness}" />

        <!-- does NOT AutoUpdate the control -->
        <Setter Property="ShowText" 
                Value="{开发者_JAVA百科DynamicResource MyLineIsArrowUsed}"/>

Now, I observed when I update the MyLineStrokeThickness the control is updated instantly. but when I update my custom dependency property MyLineIsArrowUsed there are no changes.

What should I use in order to update the custom control (line) drawing once my custom dependency property is updated?

I tried:

static void OnIsArrowUsedChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
    var s = (MyLine)source;
    s.UpdateLayout();            
}

but this does not work.

The control updates only when I move it or do other actions when it is forced to redraw itself.

In the dependency property declaration add FrameworkPropertyMetadata.AffectsMeasure

http://msdn.microsoft.com/en-us/library/system.windows.frameworkpropertymetadata.affectsmeasure.aspx