Kivy 屏幕管理器，找到屏幕实例名称？

Question

目前正在开发基于 kivy 的程序，但需要在 2 个屏幕之间传递一个变量，我正在使用屏幕管理器，需要找到“LoginScreen”的实例以获取用户名，然后将其显示在“主屏幕'

screenmanager 是否创建用户定义屏幕的实例，如果是，我如何访问此实例

如果不是我如何找到“登录屏幕”创建的实例

import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.label import Label
from kivy.uix.screenmanager import *
from kivy.config import Config

import hashlib

import sqlite3

with sqlite3.connect('scorestore.db') as db:
    cursor = db.cursor()

kivy.require("1.11.0")

Builder.load_string("""
<RegisterScreen>
    name: 'register'
    FloatLayout:
        Image:
            source: 'scorestorelogo.png'
            size_hint: 0.8, 0.8
            pos_hint: {"x":0.1 , "y":0.535}

        Label:
            text: "Name"
            pos_hint: {"x":-0.3, "y":0.275}

        TextInput:
            id: name
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.75}

        Label:
            text: "Email Address"
            pos_hint: {"x":-0.3, "y":0.1925}

        TextInput:
            id: email
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.667}

        Label:
            text: "Password"
            pos_hint: {"x":-0.3, "y":0.11}

        TextInput:
            id: password
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.584}
            password: True

        Label:
            text: "Club ID"
            pos_hint: {"x":-0.3, "y":0.0275}

        TextInput:
            id: clubid
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.501}

        Button:
            font_size: 30
            size_hint: 0.4, 0.1
            pos_hint: {"x":0.3, "y":0.35}
            text: "Register Account"
            on_press: 
                root.register_account(name.text, email.text, password.text, clubid.text)

        Button:
            font_size: 20
            size_hint: 0.15, 0.05
            pos_hint: {"x":0.82, "y":0.500}
            text: "Find Club ID"
            on_press: root.manager.current = 'find-club'

        Label:
            id: error
            text: ""
            pos_hint: {"x": 0, "y": -0.2}

        Button:
            font_size: 20
            text: "Return to login"
            size_hint: 0.2, 0.05
            pos_hint: {"x": 0.4, "y":0.15}
            on_press: root.manager.current = 'login'

<LoginScreen>
    name: 'login'
    FloatLayout:
        Image:
            source: 'scorestorelogo.png'
            size_hint: 0.8, 0.8
            pos_hint: {"x":0.1 , "y":0.535}

        Label:
            text: "User Email Address"
            pos_hint: {"x":-0.3, "y":0.1925}

        TextInput:
            id: email
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.667}

        Label:
            text: "Password"
            pos_hint: {"x":-0.3, "y":0.11}

        TextInput:
            id: password
            size_hint: 0.5, 0.05
            pos_hint: {"x":0.3, "y":0.584}
            password: True

        Button:
            font_size: 30
            size_hint: 0.4, 0.1
            pos_hint: {"x":0.3, "y":0.42}
            text: "Log in"
            on_press:
                root.login(email.text, password.text)

        Label:
            font_size: 20
            text: "or"
            pos_hint: {"x":0, "y":-0.12}

        Button:
            font_size: 30
            size_hint: 0.4, 0.1
            pos_hint: {"x":0.3, "y":0.23}
            text: "Register"
            on_press: root.manager.current = 'register'

        Label:
            id: error
            text: ""
            pos_hint: {"x":0, "y":-0.4}



<FindClubScreen>
    name: 'find-club'
    Image:
        source: 'scorestorelogo.png'
        size_hint: 0.8, 0.8
        pos_hint: {"x":0.1 , "y":0.535}

    Label:
        text: "Search club name"
        pos_hint: {"x":-0.25, "y":0.275}

    TextInput:
        id: club
        size_hint: 0.5, 0.1
        pos_hint: {"x":0.35, "y":0.7}

    Label:
        id: no_clubs
        text: ''
        pos_hint: {"x": 0.05, "y": 0}

    Label:
        id: index
        text: ""
        pos_hint: {"x": 0.05, "y": 0.07}

    Label:
        id: result_list
        text: ""
        pos_hint: {"x": 0.08, "y": -0.05}


    Button:
        font_size: 30
        size_hint: 0.3, 0.075
        pos_hint: {"x": 0.4, "y": 0.6}  
        text: "Search Clubs"
        on_press: 
            root.get_club(club.text)

    Label:
        text: "Can't see your club? Try changing your search terms"  
        pos_hint: {"x": 0.05, "y": -0.4}    

    Button:
        font_size: 30
        size_hint: 0.3, 0.075
        pos_hint: {"x": 0.4, "y": 0.15}
        text: "Register Account"
        on_press:
            root.manager.current = 'register'

<HomeScreen>
    name: 'home'
    Image:
        source: 'scorestorelogo.png'
        size_hint: 0.8, 0.8
        pos_hint: {"x":0.1 , "y":0.535}

    Label:
        id: user
        text: ""
        pos_hint: {"x": 0, "y": 0}


""")


class LoginScreen(Screen):
    def __init__(self, **kw):
        super().__init__(**kw)
        self.email = ""
        self.password = ""
        self.password_attempt = ""
        self.user_name = ""

    def get_password(self):
        cursor.execute('''SELECT password FROM Users WHERE email LIKE ?''', (self.email,))
        user_pw = cursor.fetchall()
        user_pw = str(user_pw)
        user_pw = user_pw.strip("[]")
        user_pw = user_pw.strip("()")
        user_pw = user_pw.strip(",")
        user_pw = user_pw.strip("'")
        return user_pw

    def get_user_name(self):
        cursor.execute('''SELECT name FROM Users WHERE email LIKE ?''', (self.email,))
        user_name = cursor.fetchall()
        user_name = str(user_name)
        user_name = user_name.strip("[]")
        user_name = user_name.strip("()")
        user_name = user_name.strip(",")
        user_name = user_name.strip("'")
        return user_name

    def login(self, emailText, passwordText):
        self.ids.error.text = ""
        self.email = emailText
        self.password_attempt = passwordText
        self.password = self.get_password()
        self.user_name = self.get_user_name()
        self.password_attempt = hashlib.md5(self.password_attempt.encode())
        self.password_attempt = self.password_attempt.hexdigest()

        if self.password == self.password_attempt:
            print("Login successful")
            sm.current = 'home'

        else:
            self.ids.error.text = "Login unsuccessful please check your details and try again"
            return


class RegisterScreen(Screen):
    def __init__(self, **kw):
        super().__init__(**kw)
        self.fullname = ""
        self.email = ""
        self.password = ""
        self.clubID = 0
        self.userID = 0
        self.last_user = []
        self.last_uid = 0

    def create_uid(self, last_user):
        for i in last_user:
            last_uid = i
            break

        last_uid = str(last_uid)
        last_uid = last_uid.strip("()")
        last_uid = last_uid.strip(",")
        last_uid = int(last_uid)
        userID = last_uid + 1
        return userID

    def register_account(self, nameText, emailText, passwordText, clubidText):
        self.ids.error.text = ""
        try:
            self.fullname = nameText
            self.email = emailText.lower()
            self.password = passwordText
            self.clubID = int(clubidText)
            self.userID = self.create_uid(cursor.execute('''SELECT max(userID) as userID FROM Users;'''))

        except ValueError:
            self.ids.error.text = "Invalid input check format of inputted info"
            return

        already = cursor.execute('''SELECT email FROM Users WHERE email LIKE ?''', (self.email,))
        for i in already:
            already = i
            break

        if len(already[0]) > 0:
            self.ids.error.text = "An account with that email already exists"
            return

        self.password = hashlib.md5(self.password.encode())
        self.password = self.password.hexdigest()

        cursor.execute('''INSERT INTO Users(userID, name, clubID, email, password) VALUES (?,?,?,?,?)''',
                       (self.userID, self.fullname, self.clubID, self.email, self.password))
        db.commit()

        sm.current = 'login'


class FindClubScreen(Screen):
    def __init__(self, **kw):
        super().__init__(**kw)
        self.club = ""
        self.results = []
        self.search_terms = []
        self.result_labels = []

    def get_club(self, clubText):
        self.club = clubText
        self.club = self.club.split()
        self.search_terms = []
        self.results = []
        self.result_labels = []
        for i in self.club:
            if i.lower() not in ["college", "rifle", "club", "school", "association", "and"]:
                self.search_terms.append(i)
            else:
                self.club.remove(i)

        for i in self.search_terms:
            self.results += cursor.execute('''SELECT * FROM Clubs WHERE name LIKE ?''', ('%'+i+'%',))

        self.ids.no_clubs.text = ""
        self.ids.index.text = ""
        self.ids.result_list.text = ""

        if len(self.results) == 0:
            self.ids.no_clubs.text = "No clubs with that name found"
            return

        self.ids.index.text = "ID, Club name"

        count = 0
        for i in range(len(self.results)):
            count += 1
            self.ids.result_list.text += str(self.results[i]).strip('()') + "\n"
            if count == 5:
                break


class HomeScreen(Screen):
    def __init__(self, **kw):
        super().__init__(**kw)
        self.ids.user.text = LoginScreenInstance.user_name


sm = ScreenManager(transition=FadeTransition())

sm.add_widget(LoginScreen(name='login'))
sm.add_widget(RegisterScreen(name='register'))
sm.add_widget(FindClubScreen(name='find-club'))
sm.add_widget(HomeScreen(name='home'))


class ScoreStore(App):
    def build(self):
        return sm


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

Answer 1

您将类定义与类的实例混淆了。没有 LoginScreen.user_name 这样的东西，因为没有代码可以将此属性添加到类中（也不应该有）。但是如果你创建一个类的实例，例如l = LoginScreen()，然后l.user_name 具有您在初始化类时分配的值。

相反，您需要访问您关心的LoginScreen 实例的user_name 属性。如果您不知道该怎么做，请发布一个最小的可运行示例，其中包含一个您无法建立连接的简单案例。

Answer 2

您的LoginScreen 将user_name 定义为实例级属性。这意味着，为了访问实例级属性，您必须创建您的类的实例，在您的情况下为 LoginScreen。为了解决您当前的问题，您可以更改以下代码行

self.ids.user.text = LoginScreen.user_name

到

login_screen= LoginScreen()
self.ids.user.text = login_screen.user_name

您可以在here 阅读有关实例和类级别属性的更多信息。