我希望这样可以看到循环执行的进度，但是progressbar只在循环执行后退出。我怎样才能解决这个问题？

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.progressbar import ProgressBar

class MyApp(App):
    def build(self):
        self.wid = FloatLayout()
        self.prog_bar = ProgressBar(max=99999, pos = [0, -150])
        self.wid.add_widget(self.prog_bar)
        self.prog_bar.value = 0
        for i in range(0, 99999):
            self.prog_bar.value = i
            print(i/99999)

        return self.wid
if __name__ == '__main__':
    MyApp().run()