How to stretch in width a WPF user control to its window?

Question

I have a Window with my user control and I would like to make usercontrol width equals window width. How to do that?

The user control is a horizontal menu and contains a

Answer 1

What container are you adding the UserControl to? Generally when you add controls to a Grid, they will stretch to fill the available space (unless their row/column is constrained to a certain width).