main:

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.gridlayout import GridLayout
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from kivy.uix.widget import Widget


class testclass:
    def someth(txt):
        print (txt)
        #how get  access to textinput from begin Screen here?
class BeginScreen(Screen):
    def __init__(self,**kwargs):
        super().__init__()
        self.layout =BoxLayout(orientation='vertical',padding=20,spacing=5,)
        self.btn=Label(text=str('Hello'))
        self.layout.add_widget(self.btn)
        self.btn=TextInput(id='test',text='')
        self.layout.add_widget(self.btn)
        self.btn=Button(text='Button!', on_press=testclass.someth('?'))
        # what write in ? to send textinput text to testclass.someth?
        self.layout.add_widget(self.btn)
        self.add_widget(self.layout)
        print(self.layout.ids) #why i have no ids? textinput have id

class TestApp(App):   
    from kivy.config import Config
    Config.set('graphics', 'width', '800')
    Config.set('graphics', 'height', '400')
    def build(self):
        sm = ScreenManager()
        sm.add_widget(BeginScreen(name='test'))
        return sm
TestApp().run()

那么我如何访问文本输入呢？我有 id='test' 但当我打印布局时 id 说我没有。为什么？有人可以向我解释我做错了什么，我怎样才能改正呢？

从 functools 导入部分

要访问外部方法中的文本输入，您可以使用部分函数或 lambda 函数。

self.ids

因为您没有 kv 文件，所以您得到 None 或空字典。

Note

当你的 kv 文件被解析时，kivy 会收集所有用 id 标记的小部件，并将它们放置在 self.ids 字典类型属性中。

详细请参考我下面的例子。

Example

main.py

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from functools import partial


class testclass:
    def someth(*args, txt):
        print(txt)


class BeginScreen(Screen):
    def __init__(self, **kwargs):
        super(BeginScreen, self).__init__(**kwargs)
        layout = BoxLayout(orientation='vertical', padding=20, spacing=5)
        layout.add_widget(Label(text=str('Hello')))

    # layout.add_widget(TextInput(id='test', text=''))  # id in python+kivy is deprecated
    txtInput = TextInput(text='text input')
    layout.add_widget(txtInput)
    self.ids['test'] = txtInput

    layout.add_widget(Button(text='Button!', on_press=partial(testclass.someth, txt=self.ids.test.text)))
    self.add_widget(layout)

    print("self.ids={}".format(self.ids))
    print("self.ids['test']={}".format(self.ids['test']))
    print("self.ids['test'].text={}".format(self.ids['test'].text))
    print("self.ids.test.text={}".format(self.ids.test.text))
    for key, val in self.ids.items():
        print("key={0}, val={1}".format(key, val))


class TestApp(App):
    from kivy.config import Config
    Config.set('graphics', 'width', '800')
    Config.set('graphics', 'height', '400')

    def build(self):
        sm = ScreenManager()
        sm.add_widget(BeginScreen(name='test'))
        return sm

TestApp().run()

Output