What exactly does WPF Data Binding's "RelativeSource FindAncestor" do?

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I am currently working within a WPF user control (the root element of my XAML file is "UserControl"), which I know is being hosted inside a Window. How can I access a property of the Window using data binding?

Does anyone know why simply

<Binding RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type Window}}" Path="..." />

does not work? The error message I get is:

System.Windows.Data Warning: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''.

Edit: I ended up using a variation on ArsenMkrt's approach, so have accepted his answer. However, I am still interested in finding out why FindAncestor does not "just work".

findancestor relativesource data-binding xaml wpf
4 Answers

If you are using a view model as your Window's DataContext and the property you need to bind to is from that view model then you should prefix the path with DataContext.MyPropertyPath, something like this:

<TextBox Text="{Binding DataContext.MyProperty, RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"/>

this translates as "Find me an ancestor window and then look in it's data context for MyProperty"

user_15844110
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