WPF - Adopt size of parent

The Width and Height properties are primarily designed for setting requested dimensions.

If you are using dynamic layouts with stretching, etc. bind to the ActualWidth and ActualHeight properties:

<Binding RelativeSource="{RelativeSource ...}" Path="ActualWidth"/>

I was trying to do something similar, found this to work well:

    Width="{Binding RelativeSource={RelativeSource FindAncestor, 
    AncestorType={x:Type ListBox}},Path=ActualWidth}"

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