Style DataTrigger not updating Custom Control Dependency Property - wpf

Question

I've defined a custom control that allows me to draw a series of arcs that result in a segmented circle. In this control I've defined a dependency property that allows me to set the number of segments to draw, i.e.,
public int SegmentCount
{
get => (int) GetValue( SegmentCountProperty );
set => SetValue( SegmentCountProperty, value );
}
public static readonly DependencyProperty SegmentCountProperty =
DependencyProperty.Register( nameof(SegmentCount), typeof( int ), typeof( MyCustomControl ), new PropertyMetadata( 1 ) );
I want to set this property in xaml according to a data trigger defined in a style as follows
<Style x:Key="MyCustomControlStyle" TargetType="local:MyCustomControl">
<Setter Property="SegmentCount" Value="0"/>
<Style.Triggers>
<DataTrigger Binding="{Binding IsActive}" Value="True">
<Setter Property="SegmentCount" Value="4"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsActive}" Value="False">
<Setter Property="SegmentCount" Value="0"/>
</DataTrigger>
</Style.Triggers>
</Style>
However, the "False" DataTrigger that attempts to set the SegmentCount property back to 0 doesn't appear to update the view. If I set the Stroke property as well (which i don't want to do) like this
<Style x:Key="MyCustomControlStyle" TargetType="local:MyCustomControl">
<Setter Property="SegmentCount" Value="0"/>
<Style.Triggers>
<DataTrigger Binding="{Binding IsActive}" Value="True">
<Setter Property="SegmentCount" Value="4"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsActive}" Value="False">
<Setter Property="SegmentCount" Value="0"/>
<Setter Property="Stroke" Value="Green"/>
</DataTrigger>
</Style.Triggers>
</Style>
It seems to kick things along and I get the expected view, albeit with the wrong colour now. Is there a reason why my Dependency property is not updating the view in this scenario? Do I have to tell the framework it has changed similar to a RaiseNotifyProperty changed event?

Answer 1

There is no PropertyChangedCallback registered for the SegmentCount property.
It probably just does not trigger rendering. Try to set Framework​Property​Metadata​Options.AffectsRender:
public static readonly DependencyProperty SegmentCountProperty =
DependencyProperty.Register(
nameof(SegmentCount), typeof(int), typeof(MyCustomControl),
new FrameworkPropertyMetadata(
1, FrameworkPropertyMetadataOptions.AffectsRender));