我无法从 Python 更新 Kivy 标签的内容

Question

声明这是我第一次使用Kivy。我附加的代码有效，唯一的问题是 lbl 标签不会自动更新，但只有在我按下 update 按钮时才会更新。实际上，如果我通过“更新”按钮调用 update_lbl 函数，它会起作用，当它被 unpacking_msg 自动调用时，它什么都不做。

from email import message
from kivy.app import App
from kivy.clock import Clock
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty, StringProperty
from kivy.lang import Builder
from numpy import empty
import paho.mqtt.client as mqttClient
from queue import Queue
import threading

q=Queue()
incoming_message =''
incoming_topic =''

class Manager(ScreenManager):
    pass

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

class HomeScreen(Screen):

    pass

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

class MsgDecoder ():
    
    def __init__(self,msg):
        self.msg = msg
    
    def unpacking_msg(self):
        global incoming_message
        global incoming_topic
        incoming_topic =  str(self.msg.topic)
        incoming_message = str(self.msg.payload.decode("utf-8"))
        MainApp().update_lbl()
        
#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

class MqttApp():

    def __init__(self,broker_address,port,user,password):   
        self.password = password
        self.user = user
        self.port = port
        self.broker_address = broker_address
       
    broker_address = "broker.hivemq.com"    
    port = 1883                   
    user = ""                  
    password = ""   

    try:
        client = mqttClient.Client(clean_session=True, userdata=True)               
        client.username_pw_set(user , password) 
        client.connect(broker_address,port)
        client.loop_start() 
    except:
        pass
        
    def on_connect(client, userdata, flags, rc):
        client.subscribe("kivy")

    def on_message(client, userdata, msg):
        q.put(msg)        
                    
    client.on_connect = on_connect
    client.on_message = on_message

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

class MainApp(App):  
    
    lbl_txt = StringProperty()

    def __init__(self):
            super(MainApp, self).__init__()
            self.lbl_txt = ("No message")
    
    def switch_callback(self, switchObject, switchValue):
        
        if(switchValue):
            MqttApp.client.publish("kivy", "ON")
        else:
            MqttApp.client.publish("kivy", "OFF") 

    def update_lbl(self, *args):
        self.lbl_txt=incoming_message 

 #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::  

def get_msg ():
    threading.Timer(1.0, get_msg).start()
    while not q.empty():
        msg = q.get()
        if msg is None:
            continue
        md= MsgDecoder(msg)
        md.unpacking_msg()
get_msg()

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

这是 Kivy 文件：

ScreenManager:
    HomeScreen:
        id: 'homescreen'
        
    
<HomeScreen>:
    swc: swc
    
    BoxLayout:
       

        orientation: 'vertical'
        spacing: 50
        padding: 100

        Label:
            text: 'Remote Lamp'

        Switch:
            id:swc
            on_active: app.switch_callback(*args)

        Button:
            text: "update"
            on_press: app.update_lbl()    

        Label:
            id: lbl
            text: app.lbl_txt

非常感谢任何其他有用的建议！如您所见，我不是专家。

Answer 1

问题是你的代码：

MainApp().update_lbl()

正在创建 MainApp 的新实例并调用其 update)lbl() 方法。但是，MainApp 的新实例不是您在屏幕上看到的实例。您必须调用运行 App 的 update_lbl() 方法。您可以使用 get_running_app() 方法来做到这一点。参见documentation。试试这个替换上面的行：

App.get_running_app().update_lbl()

我无法从 Python 更新 Kivy 标签的内容

I can't update the content of a Kivy label from Python

python

kivy