After various attempts I tried the hammer of explicetly setting it from code behind
Private Sub dlg_TimeGridBase_SizeChanged(ByVal sender As Object, ByVal e As System.Windows.SizeChangedEventArgs) Handles Me
Me.grdContent.Width = e.NewSize.Width - Me.grdContent.Margin.Left - Me
Me.stkContent.Width = Me.grdContent.Width - Me.stkContent.Margin.Left - Me
Me.grdRows.Width = Me.stkContent.Width - Me.grdRows.Margin.Left - Me
The Grid is nested within a stackpanel within the layout grid. The problem is that this seems to set the values well, but the width of the gid is still limited to the width it was initially rendered at as a maximum and I still can not expand it beyond that width.
I did try binding it in the xaml, but no matter what I do it does not seem to want to fill out the width wider than a fixed amount I have no clue about.
any suggestions? I want the grid to resize up its width with when the dialog size is widened no matter how big the user makes it. I do observe that the right portion (beyond the initially displayed window) never appears, but seems to be accounted for in the horizontal scrollbar, and as I expand the width past my initial width the vertical scrollbar disapears from view, but reappears when I reduce the width below the initial display width. Its as if there is a mask over the right hand side of the grid starting where the initial width first displayed with a higher z-order that prevents viewing that portion of the grid.