RecycleView with png images.

recycle.py

#In my py file I have:

from kivy.lang import Builder
from kivy.uix.recycleview import RecycleView
from kivymd.uix.list import TwoLineIconListItem, TwoLineAvatarListItem

from kivy.properties import StringProperty

from kivymd.app import MDApp

class ItemImage(TwoLineAvatarListItem):
    source = StringProperty()
    
class ScreenListItens(Screen):

    def on_kv_post(self, base_widget):
        p = Detalhe.select(Detalhe.dsdetalhe, Detalhe.cdprincipal) \
        .order_by(Detalhe.cdprincipal)

        for row in p.dicts():

            self.ids.rv.data.append(
                {
                    "viewclass": "ItemImage",
                    "source": './images/python.png',
                    "text": row['dsdetalhe'],
                    "secondary_text":"SEGUNDO TEXTO",
                    "callback": lambda x: x,
                }
            )     
            
            
class AppDesktop(MDApp):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def build(self):
        return Builder.load_file('main.kv')
        
AppDesktop().run()   




# In my kv file I have the following screen:

<ScreenListItens>:
    name: "list_itens"

    MDBoxLayout:
        orientation: 'vertical'
        spacing: dp(10)
        padding: dp(63)
                
        RecycleView:
            id: rv
            key_viewclass: 'viewclass'
            key_size: 'height'

            RecycleBoxLayout:
                padding: dp(10)
                default_size: None, dp(48)
                default_size_hint: 1, None
                size_hint_y: None
                height: self.minimum_height
                orientation: 'vertical'       
                
                
# If I don't use RecycleView the images appear beautifully. 
# Why can't I show the images?
# Why do widgets get disorganized?