Rita Rita - 3 months ago 61
Android Question

Python+kivy+SQLite: How to set label initial value and how to update label text?

everyone,

I want to use

kivy+Python
to display items from a
db
file.

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

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

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.

For this two screens design, I have two questions:

Question 1: How to update the
label text
when the
button
is clicked?

I tried with two methods:

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.

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.

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.

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()


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

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

Answer
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()

is typically how you would do this ...