Python Kivy switching between button inside Popup

i would like to ask for favor here for python kivy desktop application, i have small problem but it is so annoying. the problem that i have is switching between two buttons (Yes Button and No Button) in kivy Popup with keyboard "Tab key" is not working and also i want to be able pressing "Enter key" for the selected button processing the function.

here is my Popup looks like:

Popup screenshot

and the code of the popup is as follow:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.popup import Popup
from kivy.uix.label import Label


class testWindow(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        def yes_btn(instance):
            print("this function is called.")

        contents = BoxLayout(orientation='vertical')
        content_text = Label(text="Lanjutkan Transaksi?")
        pop_btn = BoxLayout(spacing=10)
        btn_yes = Button(text='Ya', size_hint_y=None, height=40)
        btn_no = Button(text='Tidak', size_hint_y=None, height=40)
        pop_btn.add_widget(btn_yes)
        pop_btn.add_widget(btn_no)
        contents.add_widget(content_text)
        contents.add_widget(pop_btn)

        pop_insert = Popup(title="Confirmation Message", content=contents, size_hint=(None, None), size=(300, 300))

        btn_yes.bind(on_release=yes_btn)
        btn_no.bind(on_release=pop_insert.dismiss)

        pop_insert.open()


class testApp(App):
    def build(self):
        return testWindow()


if __name__ == '__main__':
    m = testApp()
    m.run()

The popup is functioned properly when i click the button using mouse. as the popup picture above, i would like to make Yes Button focused and when i press "Enter key" popup dismiss and running the function i want. meanwhile to switch between button just press "Tab key".

i have been trying to find the way to solve the problems but still got no result, so please if anyone know how to solve my problem help me.

Solution

Here is a modification of your code that I think does what you want:

from kivy.app import App
from kivy.core.window import Window
from kivy.lang import Builder
from kivy.properties import BooleanProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.popup import Popup
from kivy.uix.label import Label
from kivy.uix.behaviors import FocusBehavior

# This is a Button that also has focus behavior
class FocusButton(FocusBehavior, Button):
    first_focus = BooleanProperty(False)

    def on_parent(self, widget, parent):
        # if first_focus is set, this Button takes the focus first
        if self.first_focus:
            self.focus = True


class MyPopup(Popup):
    def keydown(self, window, scancode, what, text, modifiers):
        if scancode == 13:
            for w in self.walk():
                if isinstance(w, FocusButton) and w.focus:
                    w.dispatch('on_press')

    def keyup(self, key, scancode, codepoint):
        if scancode == 13:
            for w in self.walk():
                if isinstance(w, FocusButton) and w.focus:
                    w.dispatch('on_release')

    def on_dismiss(self):
        Window.unbind(on_key_down=self.keydown)
        Window.unbind(on_key_up=self.keyup)

Builder.load_string('''
# provide for a small border that indicates Focus
<FocusButton>:
    canvas.before:
        Color:
            rgba: 1,1,1,1
        Rectangle:
            pos: self.x-2, self.y-2
            size: (self.size[0]+4, self.size[1]+4) if self.focus else (0,0)
''')


class testWindow(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        def yes_btn(instance):
            print("this function is called.")

        contents = BoxLayout(orientation='vertical')
        content_text = Label(text="Lanjutkan Transaksi?")
        pop_btn = BoxLayout(spacing=10)

        # set first_focus to True for this Button
        self.btn_yes = FocusButton(text='Ya', size_hint_y=None, height=40, first_focus=True)
        self.btn_no = FocusButton(text='Tidak', size_hint_y=None, height=40)
        pop_btn.add_widget(self.btn_yes)
        pop_btn.add_widget(self.btn_no)
        contents.add_widget(content_text)
        contents.add_widget(pop_btn)

        pop_insert = MyPopup(title="Confirmation Message", content=contents, size_hint=(None, None), size=(300, 300))

        self.btn_yes.bind(on_release=yes_btn)
        self.btn_no.bind(on_release=pop_insert.dismiss)

        # bind to get key down and up events
        Window.bind(on_key_down=pop_insert.keydown)
        Window.bind(on_key_up=pop_insert.keyup)

        pop_insert.open()

class testApp(App):
    def build(self):
        return testWindow()


if __name__ == '__main__':
    m = testApp()
    m.run()

This code adds FocusBehavior to a Button to create a FocusButton, and adds key down and key up processing to the MyPopup class.