Question

I’ve created a UserControl with an ItemContext DependencyProperty. This property contains the name of the property of my DataContext object the Control’s text property should bind to.

I cannot figure out how to do this in XAML. I tried several steps, I’m quite near but couldn’t find it.

Something like this:

<TextBox Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type me:UserControl}}, Path=ItemContext}" />

But here the contents of “ItemContext” is bound directly to the Text Property which I don’t want. The contents of “ItemContext” let’s say “Property1” is the name of the property in my DataContext I’d like to bind to.

In code it works like this:

this.txtValue0.SetBinding(TextBox.TextProperty, new Binding(this.ItemContext) { Mode = BindingMode.TwoWay });

Does someone have an idea?

Thanks

Answer 1

It sounds as though what you’re trying to pass an external value into the Path property of a Binding object. That is, if ItemContext‘s value is “Blob”, you want to bind to DataContext.Blob (not display the value “Blob”).

That’s easy to do in code, because you can reference the value directly (you pass this.ItemContext to your binding as a one-time value). In markup, however, you can’t do this. Instead, you’re trying to bind a value to the Path of the Binding, but you can’t (because it’s not a DependencyProperty).

I’d suggest that a much easier solution would be to create a different property on your UserControl: instead of passing in “the name of the thing you want to bind to,” why not just pass in the value of the thing?

I’m imagining that your current code looks like this:

<u:MyControl DataContext="{Binding SomeObject}" ItemContext="MyPropertyName" />

… and instead you should make it look like this:

<u:MyControl DataContext="{Binding SomeObject}" ItemValue="{Binding MyPropertyName}" />

… so the value is resolved externally of the control. Within the control, you can use @dowhilefor’s solution to bind to the value.

Hope that makes sense!