This isn't supported 'out-of-the-box' in the current MvvmCross source -
but it should be relatively straight-forward to merge the fragments and
Activity-dialog code in order to create a working sample.
The exception you list is thrown from https://github.com/slodge/MvvmCross/blob/v3/CrossUI/CrossUI.Droid/DroidResources.cs#L99
It suggests that the Setup hasn't been called - in the standard samples
(e.g. N+1 video samples) this is called via https://github.com/slodge/MvvmCross/blob/v3/Cirrious/Cirrious.MvvmCross.Dialog.Droid/MvxAndroidDialogSetup.cs#L45
So this suggests you should check the setup in your code sample - are
the resources being initialised?