Is it possible to bind PolyLineSegment.Points through xaml in ControlTemplate? - wpf

Question

Recently, I needed to change the Thumb's Template. I want to change its shape to a Triangle like so. I used a Path as its ControlTemplate. Here's the code:
<Thumb
Width="100"
Height="30"
HorizontalAlignment="Left"
VerticalAlignment="Top">
<Thumb.Template>
<ControlTemplate>
<Path Fill="Red">
<Path.Data>
<PathGeometry>
<PathFigure>
<PolyLineSegment>
<PolyLineSegment.Points>
<PointCollection>
<Point X="0" Y="0" />
<Point X="{TemplateBinding Width}" Y="{TemplateBinding Height}" />
<Point X="0" Y="{TemplateBinding Height}" />
</PointCollection>
</PolyLineSegment.Points>
</PolyLineSegment>
</PathFigure>
</PathGeometry>
</Path.Data>
</Path>
</ControlTemplate>
</Thumb.Template>
</Thumb>
You can see that I tried to bind PolyLineSegment.Points to Thumb's Width and Height.
But Visual Studio throws an error:
"Error Object of type 'System.Windows.TemplateBindingExpression'
cannot be converted to type 'System.Double'."
I don't know why it can't work. Can anyone give me a hint?

Answer 1

Finally, I found where the problem is. I found it's because Point.X or Point.Y is not Dependency Property. So that's why binding doesn't work.
I resolve this question by binding to LineSegment.
<ControlTemplate>
<Path Fill="{TemplateBinding Background}">
<Path.Data>
<PathGeometry>
<PathFigure StartPoint="0 0">
<LineSegment>
<LineSegment.Point>
<MultiBinding Converter="{StaticResource thumb2PointConverter}" ConverterParameter="rightBottom">
<Binding Path="Width" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Thumb}" />
<Binding Path="Height" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Thumb}" />
</MultiBinding>
</LineSegment.Point>
</LineSegment>
<LineSegment>
<LineSegment.Point>
<MultiBinding Converter="{StaticResource thumb2PointConverter}" ConverterParameter="leftBottom">
<Binding Path="Width" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Thumb}" />
<Binding Path="Height" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Thumb}" />
</MultiBinding>
</LineSegment.Point>
</LineSegment>
</PathFigure>
</PathGeometry>
</Path.Data>
</Path>
</ControlTemplate>