如何通过图标按钮KivyMD使用MDDropdownMenu？

from kivymd.app import MDApp
from kivy.uix.boxlayout import BoxLayout
from kivymd.uix.menu import MDDropdownMenu
from kivymd.uix.button import MDIconButton

class MainLayout(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        
        self.orientation = 'vertical'
        
        # 创建图标按钮
        self.icon_button = MDIconButton(icon="dots-vertical")
        self.icon_button.pos_hint = {'center_x': 0.5}
        self.icon_button.bind(on_release=self.show_menu)
        
        # 创建下拉菜单
        self.menu_items = [
            {'text': '选项1', 'viewclass': 'MDMenuItem'},
            {'text': '选项2', 'viewclass': 'MDMenuItem'},
            {'text': '选项3', 'viewclass': 'MDMenuItem'}
        ]
        self.menu = MDDropdownMenu(items=self.menu_items, width_mult=4)
        self.menu.bind(on_release=self.menu_callback)
        
        # 添加图标按钮和下拉菜单到布局中
        self.add_widget(self.icon_button)
        self.add_widget(self.menu)

def show_menu(self, instance):
    self.menu.open()

def menu_callback(self, instance_menu, instance_menu_item):
    print(instance_menu_item.text)
    self.menu.dismiss()

class TestApp(MDApp):
    def build(self):
        return MainLayout()


TestApp().run()