ok, after read a lot, I think that with SHOW_ALL, onResize doesn't fire, then, How I know when the user resizes the window of my app?
I have the same need here.
For instance, I have a background image (1920 x 1200) higher than the stage (1920 x 1080) so that those with 16:10 monitors don't get blank top and bottom. Then, I have a rolling tractor that scrolls from left to right of the stage. Those with 16:10 monitors get to see a flying tractor (scrolling higher than the bottom of the stage), instead of a rolling one.
When running in full screen, we both can use Capabilities.screenResolutionX and Capabilities.screenResolutionY to determine the screen size and aspect ratio as well.
Hope this helps!
Thanks for the link.