The easiest is to change window style and remove sizing frame style from there:
Window.ModifyStyle(WS_THICKFRAME, 0);
Otherwise you can also handle WM_WINDOWPOSCHANGING
, WM_GETMINMAXINFO
messages on the window and restrict window sizing as it goes.
Note that window creation you quoted in the question above is for view, that is, for child window. This is not the window you want to prevent sizing of.