Kivy: auto-sized dialog

dialog.kv

<AppDialog>:
    size_hint: 1, None
    height: grid.minimum_height

    GridLayout:
        id: grid
        size_hint_x: 0.8
        size_hint_y: None
        height: self.minimum_height
        on_height: root._align_center()
        cols: 1
        padding: 0, dp(24)
        spacing: dp(16)

dialog.py

class AppDialog(ModalView):
    def add_widget(self, *args, **kwargs):
        if self.children:
            return self.children[0].add_widget(*args, **kwargs)
        return super(AppDialog, self).add_widget(*args, **kwargs)
    
    def remove_widget(self, *args, **kwargs):
        if self.children:
            return self.children[0].remove_widget(*args, **kwargs)
        return super(AppDialog, self).remove_widget(*args, **kwargs)
    
    def clear_widgets(self, *args, **kwargs):
        if self.children:
            return self.children[0].clear_widgets(*args, **kwargs)
        return super(AppDialog, self).clear_widgets(*args, **kwargs)