如何引用屏幕管理器的屏幕

Question

我还是个新手，似乎在别处找不到我的案例。我想从app主类访问screen类中的方法：

class MainGUI(Screen):
    d_travelled = StringProperty()
    def update_distance(self,dt):
         self.d_travelled = dt

class SecondaryGUI(Screen):
    pass

class GUIManager(ScreenManager):
    pass

class WindowGUI(App):
    def __init__(self):
        super().__init__()
        self.odrive = myDrive.Motors()
        threading.Thread(target = self.RobotControl).start()

    def build(self):
        self.title = 'MyTitle'
        kv = all_imports.Builder.load_file('kv_styles/robot_3.kv')# which instantiate the GUIs
        return kv
    
    def RobotControl(self):
        while True:
            self.root.update_distance(self.odrive.encoder_cal()) <-----Error

我在WindowGUI中有我的机器人指令，需要与kivy并排运行。首先，我想在我的MainGUI上显示编码器读数。但RobotControl中的self.root指的是GUIManager。当然，这会抛出一个错误。如何在RobotControl中引用MainGUI？是否可以将def update_distance(self,dt)放入GUIManager中，并让MainGUI显示编码器读数？如果是这样的话，是怎么做的？

我的kv文件：

#:kivy 2.0
#:import utils kivy.utils
GUIManager:
    MainGUI:
    SecondaryGUI:

<MainGUI>:
    name: "main"

    BoxLayout:
        orientation: "horizontal"
        size: root.width, root.height #covers entire window
        padding: 15
        GridLayout:
            cols: 1
            spacing: 10
            size_hint_x: 0.4
            # padding_right: 50
            BoxLayout:
                orientation:"horizontal"
                size_hint: 1,.4 

                Label:
                    text: "Drop Distance"
                    size_hint: .75,0.1
                
                Button:
                    id: zero_drop
                    text: "Zero"
                    size_hint: .25,.1
                    on_press:app.odrive.zero_encoder_read()
            BoxLayout:
                orientation: "horizontal"
                TextInput:
                    id: Encoder
                    multiline: False
                    readonly: True
                    text: root.d_travelled <-------I want to display it here
                    size_hint_x: 0.75

Answer 1

从kivy discord频道到el3phanten的致谢。这是我如何解决我的问题的：

from kivy.clock import mainthread

class MainGUI(Screen):
    # Do something

class SecondaryGUI(Screen):
    pass

class GUIManager(ScreenManager):
    pass

class WindowGUI(App):
    d_travelled = StringProperty()
    def __init__(self):
        super().__init__()
        self.odrive = myDrive.Motors()
        threading.Thread(target = self.RobotControl).start()

    def build(self):
        self.title = 'MyTitle'
        kv = all_imports.Builder.load_file('kv_styles/robot_3.kv')
        return kv
    
    def RobotControl(self):
        while True:
            val = self.odrive.encoder_cal()
            self.set_val(val)

    @mainthread 
    def set_val(self, val) :
    self.d_travelled = val

和kv：

    BoxLayout:
                orientation: "horizontal"
                TextInput:
                    id: Encoder
                    multiline: False
                    readonly: True
                    text: app.d_travelled 
                    size_hint_x: 0.75