MainWindow.size strange behaviour in android

[cozimus]

Moving my first steps on toga, I run in this strange behaviour of MainWindow.size:
The following minimum working example work differently on windows and android.

import toga
from toga.style import Pack
from toga.style.pack import COLUMN

class Application(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow(title=self.formal_name)
        self.btn = toga.Button("click here", on_press=self.my_func)
        main_box = toga.Box(style=Pack(flex=1, direction=COLUMN))
        main_box.add(self.btn)
        self.main_window.content = main_box
        self.my_func()
        self.main_window.show()

    def my_func(self, widget=None):
        self.btn.text = self.main_window.size


def main():
    return Application("Application", "com.example")


if __name__ == "__main__":
    app = main()
    app.main_loop()

On windows the button text change when the application is started, and it shows the real window dimension (e.g. (640,480)), while on android when the application is started it shows (0,0). However when I press the button, my_func works ok and it gives the real window size.

My real question is: how can I get the window dimensions on the startup? My goal is to add a image to the windows that fit the windows width, something like:
toga.ImageView(my_image, style=Pack(flex=1, width=self.main_window.size[0]))
which works on windows but not on android

[freakboy3742]

The underlying problem is that at the point you're asking for the window size, the window doesn't exist yet. It won't exist until after main_window.show() is invoked and a redraw event has occurred.

I've logged this as #2274; see that ticket for an explanation and a potential workaround.

However, in terms of the way Toga tries to represent layouts, it's also not the best approach for the use case you're describing. By setting the imageView to a specific width, the layout can't dynamically adapt to size changes. The layout will work as long as the phone is in portrait mode, but if the phone rotates to landscape mode, the layout won't adapt. You'll also see this on Windows if you resize the window.

Unfortunately, this is also an area where Toga has a bug at present. If an image is smaller than the window, specifying flex=1 will cause Toga to make the image expand to fill the available space; however, if the image is larger than the window, it won't shrink the image to fit the window. I've logged this as #2275; I think I have a fix for this problem - watch the ticket for updates.

[cozimus]

Thanks a lot for your reply.
That way definitly the problem. I was working with an image bigger that the window and it wasn't shrinking ':).
Your workaround is great, that's nice!