Kivy ScreenManager 的问题（ScreenManager.current 故障）

Question

I have problem with ScreenManager that it wont change screen after password check. When the password has been checked and its all right — there is need to be switched to the main_menu screen. Now it works after next start of the programm only, because when you are typing the right password — you just see that the password is correct and thats all!

There is my main.py:

from kivy.app import App
from kivymd.theming import ThemeManager
from kivymd.label import MDLabel
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.anchorlayout import AnchorLayout
from kivy.metrics import dp, sp, pt
from kivy.properties import ObjectProperty, NumericProperty, StringProperty, BooleanProperty, ListProperty
from kivymd.toast.kivytoast import toast
from kivymd.textfields import MDTextField
from kivy.storage.jsonstore import JsonStore
from kivy.uix.textinput import TextInput
from kivy.uix.screenmanager import SlideTransition
from kivy.uix.screenmanager import NoTransition

class keyinput(MDTextField):
    pass

class Manager(ScreenManager):
    def __init__(self, **kwargs):
        super(Manager, self).__init__(**kwargs)

        psw = JsonStore('password.json')

        if psw.exists('key'):
            registeredkey = psw.get('key')['keyvalue']
            if registeredkey != '12345678':
                self.transition = NoTransition()
                self.current = 'login_screen'
            else:
                self.transition = NoTransition()
                self.current = 'main_menu'
        else:
            toast('THERE IS NO KEY IN YOUR SYSTEM!')
            self.transition = NoTransition()
            self.current = 'login_screen'

class LoginScreen(Screen):

    def keycheck(self):

        psw = JsonStore('password.json')

        if self.kinput.text == '12345678':
            toast('KEY IS CORRECT')
            mngr = Manager()
            mngr.transition = NoTransition()
            mngr.current = 'main_menu'
            psw.put('key', keyvalue=str(self.kinput.text))
        elif len(self.kinput.text) > 8:
            toast('Too much text!')
        else:
            toast('KEY IS INCORRECT!')

class MainMenu(Screen):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        kinput = ObjectProperty(None)

        self.menu_items = [
                {
                    "viewclass": "MDMenuItem",
                    "text": "text%d" % i,
                    "callback": self.callback,
                }
                for i in range(1, 3)
            ]

        self.menu_button = None

    def change_variable(self, value):
        print("\nvalue=", value)
        self.VARIABLE = value
        print("\tself.VARIABLE=", self.VARIABLE)

    def callback(self, *args):
        toast(args[0])

class MainApp(App):
    title = "KivyMD MDDropdownMenu Demo"
    theme_cls = ThemeManager()

    def build(self):
        return Manager()

if __name__ == "__main__":
    MainApp().run()

There is my main.kv:

#:import MDDropdownMenu kivymd.menus.MDDropdownMenu
#:import MDRaisedButton kivymd.button.MDRaisedButton
#:import MDLabel kivymd.label.MDLabel

<OptionalLabel@MDLabel>:
    halign: 'center'
    font_size: dp(12)

<MDRB@MDRaisedButton>:
    size_hint: None, None
    size: 3 * dp(48), dp(48)
    pos_hint: {'center_x': 0.5, 'center_y': 0.5}
    opposite_colors: True

<keyinput>:
    size_hint_x: 0.5
    halign: 'center'
    pos_hint: {'center_x': .5, 'center_y': .5}
    max_text_length: 8

<Manager>:
    LoginScreen:
        id: login_screen
        name: 'login_screen'
    MainMenu:
        id: main_menu
        name: 'main_menu'

<LoginScreen>:
    kinput: kinput
    AnchorLayout:
        anchor_y: 'center'
        BoxLayout:
            orientation: 'vertical'
            size_hint: 0.5, 0.5
            pos_hint: {'center_x': 0.5, 'center_y': 0.5}
            spacing: dp(10)
            MDRB:
                text: 'Login'
                on_release:
                    root.keycheck()
            keyinput:
                id: kinput
                hint_text: "Login password"

<MainMenu>:
    AnchorLayout:
        anchor_y: 'center'
        BoxLayout:
            orientation: 'vertical'
            size_hint: 0.5, 0.5
            pos_hint: {'center_x': 0.5, 'center_y': 0.5}
            spacing: dp(10)
            OptionalLabel:
                text: 'You have logged in'

Thanks for attention and help!

Answer 1

The Manager in your kv code is actually a different manager than the one in your keycheck function (you have instantiated a new object of your Manager class). Try using self.manager and self.manager.current = "whatever" in your keycheck function instead of mgr = Manager(). The manager attribute of a Screen should refer to it's ScreenManager. kivy.org/doc/stable/api-kivy.uix.screenmanager.html

Erik