In my UI XAML I\'m essentially inheriting from a class \"BaseView\" that contains functionality common to several forms, however this is preventing the designer from display
Yet another possible cause.
I have a user control which has child controls which generate events e.g. selection_changed on list control. The select_changed event handler makes changes to other child controls.
During initialisation the selected item property of the list box gets changed and triggers a selection_changed event. The handler tries to update the other child controls but cannot because they have not yet been instantiated. This leads to a null pointer exception and causes the problem.
Once the null pointer problem was handled the control was able to be instantiated and appeared in the parent control.