UserControl's DataContext

Question

I'm creating a UserControl I want to use something like this:

<controls:ColorWithText Color="Red" Text="Red color" /> 

So far, I've implemented similar controls like this:

<UserControl x:Class="Namespace.ColorWithText" Name="ThisControl">     <StackPanel Orientation="Horizontal" >         <Border Width="15" Height="15" Background="{Binding Color, ElementName=ThisControl}" />         <TextBlock Text="{Binding Text, ElementName=ThisControl}" />     </StackPanel> </UserControl> 

where Color and Text are dependency properties of the control defined in code. This works, but specifying ElementName every time seems unnecessary.

Another option that works is using

<UserControl x:Class=… DataContext="{Binding ElementName=ThisControl}" Name="ThisControl"> 

and not specifying ElementNames, but that doesn't seem like a clean solution to me either.

I have two questions:

1. Why doesn't <UserControl DataContext="{RelativeSource Self}"> work?
2. What is the best way to do something like this?

Answer 1

For first one, try :

<UserControl DataContext="{Binding RelativeSource={RelativeSource Self}}"> 

And for second question, I think using ElementName or AncestorBinding is best way to bind to UserControl's properties.

Answer 2

Why can't you use <UserControl DataContext="{RelativeSource Self}">?

This is how you would use the control

<Grid DataContext="{StaticResource ViewModel}">     <!-- Here we'd expect this control to be bound to -->     <!-- ColorToUse on our ViewModel resource          -->     <controls:ColorWithText Color="{Binding ColorToUse}" /> </Grid> 

Now because we've hardcoded our data-context in the control it will instead attempt to lookup ColorToUse property on the ColorWithText object not your ViewModel, which will obviously fail.

This is why you can't set the DataContext on the user control. Thanks to Brandur for making me understand that.

What is the best way to do something like this?

Instead you should set the DataContext in the first child UI element in your control.

In your case you want

<StackPanel    DataContext="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"   Orientation="Horizontal" > 

Now you have a DataContext which refers to your control so you can access any properties of that control using relative bindings.