KivyMD update: MDDropdownMenu.open() generates an error

Question

After updating an old project after a couple of years, I got an error:

TypeError: MDDropdownMenu.open() takes 1 positional argument but 2 were given

The relevant code (it used to work, two years ago), main.py:

    def build(self):
        ...
        return Builder.load_file("main.kv")

    def on_start(self):
        ...
        self.menu_lang_append()
    ...
    ...

    def menu_lang_append(self):
        self.menu_lang = MDDropdownMenu(width_mult=2)
        for lng in co_lang.LANG:
            self.menu_lang.items.append(
                {
                    "viewclass": "MDMenuItem",
                    "text": lng,
                    "callback": self.menu_lang_callback,
                }
            )

main.kv:

MDBottomAppBar:
    MDToolbar:
        id: ps_toolbar
        title: T["co-toolbar-title"]
        icon: ACTION_ICON
        type: "bottom"
        animate_action_button: False
        next_icon: app.pulse_icon_counter() # Not a callback.
        on_action_button: app.discovery_request()
        right_action_items: [ ['minus-box-outline', lambda x: app.discovery_clean()], ['earth-box', lambda x: app.menu_lang.open(x)], ['dots-vertical', lambda x: app.menu_main.open(x)], ]

A very similar case here, unresolved.

I tried to add the caller like this, no luck and no wonder; runtime errors

main.py:

    self.menu_lang = MDDropdownMenu(width_mult=2, caller=self.root.ids.ps_toolbar)

or

    self.menu_lang = MDDropdownMenu(width_mult=2, caller=self.root.ids.ps_toolbar.right_action_items)

main.kv:

    right_action_items: [... , ['earth-box', lambda x: app.menu_lang.open()], ...]

Software:

[tool.poetry.dependencies]
python = "^3.10"
Kivy = "^2.1.0"
kivymd = "^0.104.2"

Answer 1

According to #1203, copy/paste/run example:

from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.clock import Clock
from kivy.metrics import dp

from kivymd.app import MDApp
from kivymd.uix.menu import MDDropdownMenu


KV = """
BoxLayout:

    MDBottomAppBar:

        MDToolbar:
            id: toolbar
            title: "co-toolbar-title"
            icon: "eye"
            type: "bottom"
            animate_action_button: False
            right_action_items: [['earth-box', lambda x: app.menu_lang_open(x)]]
"""


class Contero(MDApp):
    menu_lang = ObjectProperty()

    def menu_lang_open(self, button):
        self.menu_lang.caller = button
        self.menu_lang.open()

    def menu_item_lang_callback(self, lng):
        self.menu_lang.dismiss()
        # Handle lng.

    def menu_lang_append(self):
        items = []

        for lng in ["EN", "RU"]:
            items.append(
                {
                    "viewclass": "OneLineListItem",
                    "text": lng,
                    "height": dp(48),
                    "on_release": lambda x=lng: self.menu_item_lang_callback(x),
                }
            )
        self.menu_lang = MDDropdownMenu(
            width_mult=2,
            items=items,
            caller=self.root.ids.toolbar.ids.right_actions.children[0],
        )

    def build(self):
        return Builder.load_string(KV)

    def on_start(self):
        def on_start(interval):
            self.menu_lang_append()

        Clock.schedule_once(on_start)


Contero().run()