问题描述

大家，

我想使用 kivy+Python 来显示 db 文件中的项目.

I want to use kivy+Python to display items from a db file.

为此，我之前问过一个问题:Python+kivy+SQLite: How一起使用

To this purpose I have asked a question before: Python+kivy+SQLite: How to use them together

链接中的应用程序包含一个屏幕.它工作得很好.

The App in the link contains one screen. It works very well.

今天我已将应用程序更改为 两个 屏幕.第一屏没有特殊要求，只是将App引导到第二屏.在 second screen 中有一个 label 和一个 button.通过单击 button 我想更改 label text.label text 指的是我在上面链接中的 db 文件中的 car type.

Today I have changed the App to two screens. The first screen has no special requirement but to lead the App to the second screen. In the second screen there is a label and a button. By clicking the button I want to have the label text changed. The label text refers to the car type from the db file that I have in the link above.

对于这两个屏幕的设计，我有两个问题:

For this two screens design, I have two questions:

问题一:点击按钮时如何更新label text?

我尝试了两种方法:

方法一: self.ids.label.text = str(text)
它向我显示了错误消息: AttributeError: 'super' object has no attribute '__getattr__' 我用谷歌搜索了很多，但仍然无法理解.

Method A: self.ids.label.text = str(text)
It shows me the error message: AttributeError: 'super' object has no attribute '__getattr__' I have googled a lot but still cannot understand.

方法B: self.ids["label"].text = str(text)它向我显示错误消息: KeyError: 'label' 我很困惑，因为我定义了 label.

Method B: self.ids["label"].text = str(text) It shows me the error message: KeyError: 'label' I am confused because I have the label defined.

问题2:如何将label origin text设置为一种车型，这样每次第二屏显示时，已经有车型显示了.

Question 2: How to set the label origin text to one of the car type, so that everytime the second screen is shown, there is already a car type shown.

代码如下:(db文件请参考上面的链接)

Here is the code: (For the db file please refer to the link above.)

# -*- coding: utf-8 -*-
from kivy.app import App
from kivy.base import runTouchApp
from kivy.lang import Builder
from kivy.properties import ListProperty
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.gridlayout import GridLayout
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.uix.widget import Widget
from kivy.graphics import Rectangle
from kivy.properties import NumericProperty, StringProperty, BooleanProperty, ListProperty
from kivy.base import runTouchApp
from kivy.clock import mainthread

import sqlite3
import random

class MyScreenManager(ScreenManager):

    def init(self, **kwargs):
        super().__init__(**kwargs)

        @mainthread  # execute within next frame
        def delayed():
            self.load_random_car()
        delayed()

    def load_random_car(self):
        conn = sqlite3.connect("C:\test.db")
        cur = conn.cursor()

        cur.execute("SELECT * FROM Cars ORDER BY RANDOM() LIMIT 1;")

        currentAll = cur.fetchone()
        conn.close()
        currentAll = list(currentAll)   # Change it from tuple to list

        print currentAll

        current    = currentAll[1]
        print current
        self.ids.label.text = str(current)    # Method A
#        self.ids["label"].text = str(current) # Method B 

class FirstScreen(Screen):
    pass

class SecondScreen(Screen):
    pass

root_widget = Builder.load_string('''
#:import FadeTransition kivy.uix.screenmanager.FadeTransition
MyScreenManager:
    transition: FadeTransition()
    FirstScreen:
    SecondScreen:

<FirstScreen>:
    name: 'first'
    BoxLayout:
        orientation: 'vertical'
        Label:
            text: "First Screen"
            font_size: 30
        Button:
            text: 'Go to 2nd Screen'
            font_size: 30
            on_release:  app.root.current = 'second'

<SecondScreen>:
    name: 'second'
    BoxLayout:
        orientation: 'vertical'
        Label:
            id: label
            text: 'click to get a new car'   # I want its text changed when the button is clicked everytime. And its original text value should be one of the random car type from the db file.
            font_size: 30
        Button:
            text: 'Click to get a random car'
            font_size: 30
            on_release:  app.root.load_random_car()

''')

class ScreenManager(App):
    def build(self):
        return root_widget

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

我从互联网上阅读了很多内容，但我无法全部理解.:-(

I have read a lot from internet, but I cannot understand them all. :-(

请帮助我更正代码.非常感谢！

Please help me to correct the code. Thank you so much!

推荐答案

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import StringProperty
from kivy.uix.widget import Widget

Builder.load_string("""
<ScreenX>
    BoxLayout:
        orientation: 'vertical'
        Label:
            text: root.label_text
        Button:
            text: 'Click Me'
            on_release: root.on_clicked_button()
""")

class ScreenX(Widget):
    label_text = StringProperty("Default Value")
    def on_clicked_button(self):
        self.label_text = "New Text!"


class MyApp(App):
    def build(self):
        return ScreenX()

MyApp().run()

通常是你会这样做的方式......

is typically how you would do this ...

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