Binding to an element within a UserControl

Question

Say I have a user control like the one below, how would I bind something to the ActualWidth of the "G1" grid from outside of the control?

<UserControl x:Class="Blah">
  <WrapPanel>
    <Grid x:Name="G1">
      ...
    </Grid>
    <Grid>
      ...
    </Grid>
  </WrapPanel>
</UserControl>

Answer 1

Can you expose the ActualWidth as a public property and set it in your parent's page for example?

Answer 2

If you want to bind to an external control where you use this user control, declare a DependancyProperty at your UserControl code behind and then Bind G1 to that property. And bind the external control's property to the UserControl's Dependancy propery. It is like a 2 level of indirection.

Answer 3

If you mean with outside the control, not as Content of the control, you can use ElementName in the Binding like so:

{Binding ElementName=G1, Path=ActualWidth}

If you mean outside the control in another Xaml file, then you can try to use the Path property if your control is in the scope of the other control:

{Binding ElementName=ParentControl, Path=G1.ActualWidth}

However I would advise against this design, because you may change the name of G1 one day, and you would never know of any Bindings that might break...

HTH