How to use Python Kivy RecycleView in another layout without using Kivy language?

Question

I want to use RecycleView in another layout without using Kivy language, but I couldn't display the data on the Window. What did I write bad or miss in my code?
I know kv language is good, but I don't want to use it in this small project.

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.recycleboxlayout import RecycleBoxLayout
from kivy.uix.recycleview import RecycleView

class MainWidget(FloatLayout):
    def __init__(self):
        super().__init__()
        self.create_layouts()

    def create_layouts(self):
        self.create_recycle_view()

    def create_recycle_view(self):
        recycle_view = RecycleView()
        recycle_view.data = [{'text': str(x)} for x in range(20)]
        recycle_view.viewclass = 'Label'
        recycle_box_layout = RecycleBoxLayout()
        recycle_box_layout.size_hint = (1, 0.2)
        recycle_view.add_widget(recycle_box_layout)
        self.add_widget(recycle_view)

class MainApp(App):
    def build(self):
        return MainWidget()

Answer 1

There seem to be some strange side effects with some of the RecycleView classes, resulting in viewclass being set to None. So setting viewclass must be done later than in your code. Also, I believe that the building of the RecycleView should not be done in the __init__() method of the MainWidget. So, based on that, a modified version of your code that works is:

from kivy.app import App
from kivy.clock import Clock
from kivy.metrics import dp
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.recycleboxlayout import RecycleBoxLayout
from kivy.uix.recycleview import RecycleView


class MainWidget(FloatLayout):

    def create_layouts(self):
        self.create_recycle_view()

    def create_recycle_view(self):
        recycle_box_layout = RecycleBoxLayout(default_size=(None, dp(56)), default_size_hint=(1, None),
                                              size_hint=(1, None), orientation='vertical')
        recycle_box_layout.bind(minimum_height=recycle_box_layout.setter("height"))
        recycle_view = RecycleView()
        recycle_view.add_widget(recycle_box_layout)
        recycle_view.viewclass = 'Label'
        self.add_widget(recycle_view)
        recycle_view.data = [{'text': str(x)} for x in range(20)]


class MainApp(App):
    def build(self):
        Clock.schedule_once(self.add_rv)
        return MainWidget()

    def add_rv(self, dt):
        self.root.create_layouts()


MainApp().run()

This code uses Clock.schedule_once() (in the build() method of the App) to build the RecycleView. Also, the height of the RecycleBoxLayout is bound to its minimum_height property.