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python - Kivy - 在其他屏幕中创建的访问实例

问题描述

我在我的第一个 Screen 中创建了一个类（Player 类）的一些实例，并希望在另一个 Screen 中访问这些实例（及其数据）。这个想法是这样的：

我在下面的代码中标记了我尝试访问实例的位置，但出现了错误：

AttributeError: 'NoneType' object has no attribute 'get_screen'

我的问题是：如何访问玩家点ThirdRound(Screen) class以便在标签上显示他们的点并在按下 +/- 按钮时更改点？

（我搜索了类似的案例，但无法将它们应用于我的案例。）

.py 文件：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.textinput import TextInput
from kivy.uix.gridlayout import GridLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.properties import ObjectProperty, NumericProperty


class Player:
    def __init__(self, name):
        self.name = name
        self.points = 0

    def reset_points(self):
        self.points = 0

    def add_point(self, *args):
        self.points += 1

    def subtract_point(self, *args):
        self.points -= 1


class WelcomeWindow(Screen):
    # Introduce names of the 4 players
    def __init__(self, **kwargs):
        super(WelcomeWindow, self).__init__(**kwargs)
        self.name = "welcomewindow"

        # Create global layout of HOME screen
        global_layout = GridLayout(rows=3)
        self.add_widget(global_layout)

        # Some code with labels and buttons

        # Create button to go to next screen
        go_further_button = Button(text="Go to first round")
        go_further_button.bind(on_release=self.go_further)
        global_layout.add_widget(go_further_button)

    def go_further(self, *args):
        #Give names to players
        self.player1 = Player("name1") # <--- 4 player instances are created here
        self.player2 = Player("name2")
        self.player3 = Player("name3")
        self.player4 = Player("name4")

        self.manager.current = "thirdround"
        self.manager.transition.direction = "left"


class ThirdRound(Screen):
    def __init__(self, **kwargs):
        super(ThirdRound, self).__init__(**kwargs)
        self.name = "thirdround"

        welcome_window = self.manager.get_screen('welcomewindow') # <--- Trying to access player instances here but failed
        self.player1_points = welcome_window.player1.points


    def change_label(self, add_sub, *args): # <--- method which will change the points of the player instance

        label = self.ids['testlabel']
        if add_sub == 'add':
            label.text = 'should add one point'
        elif add_sub == 'sub':
            label.text = 'should subtract one point'


kv = Builder.load_file("Kingen.kv")

WindowManager = ScreenManager()
WindowManager.add_widget(WelcomeWindow())
WindowManager.add_widget(ThirdRound())


class KingenApp(App):

    def build(self):
        return WindowManager


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

.kv 文件：

<ThirdRound>:

    GridLayout:
        rows: 3

        Label:
            id: testlabel
            text: 'shows number of points here'

        Button:
            text: "+"
            on_release: root.change_label('add')

        Button:
            text: "-"
            on_release: root.change_label('sub')

标签： pythonclasskivykivy-language

解决方案

The __init__() method of ThirdRound is called at the line:

WindowManager.add_widget(ThirdRound())

Specifically, the ThirdRound() is executed before the WindowManager.add_widget, so the ThirdRound instance does not have its manager yet set when its __init__() is executed, so it is still None. Try moving the code that accesses the manager till it is needed. Something like this:

class ThirdRound(Screen):
    def __init__(self, **kwargs):
        super(ThirdRound, self).__init__(**kwargs)
        self.name = "thirdround"

    def change_label(self, add_sub, *args): # <--- method which will change the points of the player instance
        welcome_window = self.manager.get_screen('welcomewindow')

        label = self.ids['testlabel']
        if add_sub == 'add':
            welcome_window.player1.points += 1
            label.text = str(welcome_window.player1.points)
        elif add_sub == 'sub':
            welcome_window.player1.points -= 1
            label.text = str(welcome_window.player1.points)

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