Question

I have a databinding problem in WPF.

I would like to “customise” a slider in a way that the thumb grows when you move the slider to the right and the thumb shrinks when you move the slider to the left.

So I edited the template for the slider and changed the look of the slider so the slider looks like I want it to.

But now I have to bind the height of the thumb to the value of the slider but I do not know how that works.

I did some simple data binding things but I cannot figure out how I can bind this “thumb height” that’s inside of my slider’s template to the slider’s value that’s inside the User Control where my slider is in.

So how can I do it?

Answer 1

You can use RelativeSource binding (Height="{Binding Value, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Slider}}}").

Here is an example of the thumb style, that depends on Slider.Value:

<Style x:Key="SliderThumbStyle" TargetType="{x:Type Thumb}">
  <Setter Property="SnapsToDevicePixels" Value="true"/>
  <Setter Property="OverridesDefaultStyle" Value="true"/>
  <Setter Property="Width" Value="14"/>
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="{x:Type Thumb}">
        <Ellipse 
          Name="Ellipse" 
          Fill="#C0C0C0"
          Stroke="#404040" 
          Height="{Binding Value, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Slider}}}"
          StrokeThickness="1" />
        <ControlTemplate.Triggers>
          <Trigger Property="IsMouseOver" Value="True">
            <Setter TargetName="Ellipse" Property="Fill" Value="#808080"/>
          </Trigger>
          <Trigger Property="IsEnabled" Value="false">
            <Setter TargetName="Ellipse" Property="Fill" Value="#EEEEEE"/>
          </Trigger>
        </ControlTemplate.Triggers>
      </ControlTemplate>
    </Setter.Value>
  </Setter>
</Style>

Hope this helps.

Cheers Anvaka