WPF TemplateBinding vs RelativeSource TemplatedParent

Question

What is the difference between these 2 bindings:

<ControlTemplate TargetType="{x:Type Button}">
   <Border BorderBrush="{TemplateBinding Property=Background}">
      <ContentPresenter />
   </Border>
</ControlTemplate>

and

<ControlTemplate TargetType="{x:Type Button}">
   <Border BorderBrush="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Background}">
      <ContentPresenter />
   </Border>
</ControlTemplate>

?

Answer 1

TemplateBinding is not quite the same thing. MSDN docs are often written by people that have to quiz monosyllabic SDEs about software features, so the nuances are not quite right.

TemplateBindings are evaluated at compile time against the type specified in the control template. This allows for much faster instantiation of compiled templates. Just fumble the name in a templatebinding and you'll see that the compiler will flag it.

The binding markup is resolved at runtime. While slower to execute, the binding will resolve property names that are not visible on the type declared by the template. By slower, I'll point out that its kind of relative since the binding operation takes very little of the application's cpu. If you were blasting control templates around at high speed you might notice it.

As a matter of practice use the TemplateBinding when you can but don't fear the Binding.

Answer 2

TemplateBinding - More limiting than using regular Binding

• More efficient than a Binding but it has less functionality
• Only works inside a ControlTemplate's visual tree
• Doesn't work with properties on Freezables
• Doesn't work within a ControlTemplate's Trigger
• Provides a shortcut in setting properties(not as verbose),e.g. {TemplateBinding targetProperty}

Regular Binding - Does not have above limitations of TemplateBinding

• Respects Parent Properties
• Resets Target Values to clear out any explicitly set values
• Example: <Ellipse Fill="{Binding RelativeSource={RelativeSource TemplatedParent},Path=Background}"/>

Answer 3

One more thing - TemplateBindings don't allow value converting. They don't allow you to pass a Converter and don't automatically convert int to string for example (which is normal for a Binding).

Answer 4

TemplateBinding is a shorthand for Binding with TemplatedParent but it does not expose all the capabilities of the Binding class, for example you can't control Binding.Mode from TemplateBinding.

Answer 5

RelativeSource TemplatedParent

This mode enables tie a given ControlTemplate property to a property of the control that the ControlTemplate is applied to. To well understand the issue here is an example bellow

<Window.Resources>
    <ControlTemplate x:Key="template">
        <Canvas>
            <Canvas.RenderTransform>
                <RotateTransform Angle="20"/>
            </Canvas.RenderTransform>
            <Ellipse Height="100" Width="150" 
                     Fill="{Binding 
                RelativeSource={RelativeSource TemplatedParent},
                Path=Background}">

            </Ellipse>
            <ContentPresenter Margin="35" 
                      Content="{Binding RelativeSource={RelativeSource  
                      TemplatedParent},Path=Content}"/>
        </Canvas>
    </ControlTemplate>
</Window.Resources>

<Canvas Name="Parent0">
    <Button   Margin="50" 
              Template="{StaticResource template}" Height="0" 
              Canvas.Left="0" Canvas.Top="0" Width="0">
        <TextBlock FontSize="22">Click me</TextBlock>
    </Button>
</Canvas>

If I want to apply the properties of a given control to its control template then I can use the TemplatedParent mode. There is also a similar one to this markup extension which is the TemplateBinding which is a kind of short hand of the first one, but the TemplateBinding is evaluated at compile time at the contrast of the TemplatedParent which is evaluated just after the first run time. As you can remark in the bellow figure, the background and the content are applied from within the button to the control template.

Answer 6

I thought TemplateBinding does not support Freezable types (which includes brush objects). To get around the problem. One can make use of TemplatedParent

Answer 7

They are used in a similar way but they have a few differences. Here is a link to the TemplateBinding documentation: http://msdn.microsoft.com/en-us/library/ms742882.aspx