Question

I have a wpf cusotm control derived from combobox System.Windows.Controls.ComboBox the control template is redefined and the popup (PART_Popup) contains a DataGrid and some other control. I use it in two places – in TabControl(,Grid) and in a Window(Grid,,Grid). When the DataGrid is resized either by dragging columns or from code the behavior is different: in window the Popup resizes in TabControl Popup remains the same and a scrollbar appears if necessary.

I need to know what can cause such difference.

Edit
Datagrid is has HorizontalAlignment=”Stretch”

Answer 1

I find it. By mistake there was

  Popup.Width=Me.Width

instead of

 Popup.Width=Me.ActualWidth

This caused resizability in case when the Me.Width was not set.