test_optioncontainer_get_it_tab_view.py

import toga
from colosseum import CSS

class StartApp(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow(self.name)
        self.main_window.app = self

        self.outer_box = toga.Box()

        all_tests_box = toga.Tree(['Tests'])
        problems_box = toga.Tree(['Problems'])
        self.notebook = toga.OptionContainer(content=[
                                        ('All tests', all_tests_box),
                                        ('Problems', problems_box)])

        self.button = toga.Button('Print ID', on_press=self.printCurrentID,
                                style=CSS(margin=50))

        self.outer_box.add(self.notebook)
        self.outer_box.add(self.button)

        self.main_window.content = self.outer_box
        self.main_window.show()

    def printCurrentID(self, button):
        print(self.notebook.selected['id'])

def main():
    app = StartApp('ProgressBar Test', 'org.pybee.test')
    app.main_loop()

if __name__ == '__main__':
    main()

Hello! I want to use the optioinCintainer widget to add tab views to my app, when I type briefcase dev, it works fine on Windows systems, but after I typebriefcase package android, and install it on my android phone and open it, there is nothing appeare on my screen but a title of the app...How could this happen? Is there something wrong? How can I add tab views to my android app?