从一个屏幕类获取变量到另一个屏幕类（KivyMD 问题）

Question

我正在构建一个 KivyMD 应用程序，但是我在将一个 Screen 类中定义的变量转换为另一个 Screen 类时遇到了一些问题。请参阅下面的脚本：

from kivymd.app import MDApp, Builder
from kivy.core.window import Window
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.properties import StringProperty
from api import gen_5_images

# --- this changes the app's default background --- #
Window.clearcolor = (.9, .9, .9, 1)
Window.size = (400, 500)

class HomeScreen(Screen):
    source = StringProperty()
    def __init__(self, **kwargs): 
        super(HomeScreen, self).__init__(**kwargs)
        self.text = 'dog'

    def get_text(self):
        self.text = self.ids.input.text
        return self.text

class ResultsScreen(HomeScreen):
    source = StringProperty()
    def on_manager(self, *args):
        # gets run when manager property is changed
        self.urls = gen_5_images(self.manager.get_screen('home').text)
        self.source = self.urls[0]
        
class Main(MDApp):
    def build(self):
        Builder.load_file("layout.kv")
        sm = ScreenManager()
        sm.add_widget(HomeScreen(name='home'))
        sm.add_widget(ResultsScreen(name='results'))
        return sm

Main().run()

当我从 HomeScreen 切换到 ResultsScreen 时，我得到变量“dog”（在 HomeScreen 的在里面) 作为文本，我想要“get_text”函数的输出。

请参阅下面我的 .kv 文件：

#:import hex kivy.utils.get_color_from_hex
<HomeScreen>:
    name: 'home'
    MDFloatLayout:
        md_bg_color: hex('#003153') # background color
        MDLabel:
            text: "DreamGen"
            color: hex('#f5deb3')
            halign: "center"
            pos_hint: {"center_x": .5, "center_y": .9}
            font_size: "40sp"
            font_name: "Pacifico"
        MDTextField:
            id: input
            hint_text: "I had a dream..."
            hint_text_color_normal: hex("#00aae4")
            hint_text_color_focus: hex("#00aae4")
            helper_text_color_focus: hex("#00aae4")
            line_color_normal: hex('#003153') #make line color of background
            line_color_focus: hex('#003153') #make line color of background
            helper_text: "Write what comes to your mind"
            helper_text_mode: "on_focus"
            text_color_focus: hex('#add8e6') # color of text clicked
            text_color_normal: hex('#add8e6') # color of text without clicked
            mode: "rectangle"
            multiline: True
            size_hint_x: 0.7
            size_hint_y: 0.5
            pos_hint: {"center_x": .5, "center_y": .5}
        MDFillRoundFlatButton:
            text: "Generate"
            text_color: hex('#003153')
            md_bg_color: hex('#add8e6')
            pos_hint: {"center_x": .5, "center_y": .1}
            font_size: "15sp"
            on_release: 
                root.get_text()
                root.manager.current = "results"

<ResultsScreen>:
    name: 'results'
    MDFloatLayout:
        md_bg_color: hex('#003153') # background color
        MDLabel:
            text: "DreamGen"
            color: hex('#f5deb3')
            halign: "center"
            pos_hint: {"center_x": .5, "center_y": .9}
            font_size: "40sp"
            font_name: "Pacifico"
        AsyncImage:
            size_hint: None,None
            size: root.height, root.height
            source: root.source
            mipmap: True
        MDFillRoundFlatButton:
            text: "Try again!"
            text_color: hex('#003153')
            md_bg_color: hex('#add8e6')
            pos_hint: {"center_x": .5, "center_y": .1}
            font_size: "15sp"
            on_release: root.manager.current = "home"

如果有人可以帮助我，我将不胜感激。

Answer 1

你的代码：

self.urls = gen_5_images(HomeScreen().text)

正在创建 HomeScreen 的新实例并访问该新实例的 text 变量。 HomeScreen 的新实例不是您的 GUI 中使用的实例。要访问 HomeScreen 的正确实例，请尝试将该代码更改为：

self.urls = gen_5_images(self.manager.get_screen('home').text)

糟糕，该代码可以工作，但不能在 __init__() 方法中使用，因为当时尚未设置 manager 属性。您可以等待 manager 属性被设置来处理。尝试更换：

class ResultsScreen(HomeScreen):
    source = StringProperty()
    def __init__(self, **kwargs):
        super().__init__()
        self.urls = gen_5_images(HomeScreen().text)
        self.source = self.urls[0]

和：

class ResultsScreen(HomeScreen):
    source = StringProperty()

    # def __init__(self, **kwargs):
    #     super().__init__()
    #     # self.urls = gen_5_images(HomeScreen().text)
    #     # self.source = self.urls[0]

    def on_manager(self, *args):
        # gets run when manager property is changed
        self.urls = gen_5_images(self.manager.get_screen('home').text)
        self.source = self.urls[0]