In a Kivy form, how to add a new button dinamically to RecycleView using Python3?

Question

I have a Kivy form with one Recycleview. I would dinamically add a button to my Recycleview, by clicking a simple Button. My Python3 script:

from kivy.app import App
from kivy.lang.builder import Builder
from kivy.uix.recycleview import RecycleView
class RV(RecycleView):
    def __init__(self, **kwargs):
        super(RV, self).__init__(**kwargs)
        self.data=[]
class app(App):
    rv=RV()
    def build(self):
        return Builder.load_file('lab.kv')
    def add_to_rv(self):
        self.rv.data.append('ok')
        # which command i should use to show new button in recycleview with new data?
app().run()

My kv file:

BoxLayout:
    RV:
        id:rv
        viewclass:'Button'
        RecycleBoxLayout:
            default_size: None, dp(56)
            default_size_hint: 1, None
            size_hint_y: None
            height: self.minimum_height
            orientation: 'vertical'
    Button:
        text:'ADD TO RV'
        on_press:app.add_to_rv()

Answer 1

Your add_to_rv() method is adding to the data of self.rv. But self.rv is defined in the statement:

rv=RV()

which creates a new instance of RV. However, that instance of RV is not used in your GUI. The instance of RV that is displayed in your GUI is built by the line of code:

return Builder.load_file('lab.kv')

And those two instances are not related. The fix is to access the correct instance of RV in your add_to_rv() method like this:

def add_to_rv(self):
    self.root.ids.rv.data.append({'text': 'ok'})

Also, note that the data is a list of dictionaries. And you can eliminate the rv=RV() line.