I have a Flex application running correctly when my resolution is 1152 per 864. If I set the resolution to a smaller value I got the horizontal scroll bar on, but I would like the screen adjusted automatically to the resolution of the screen. There should be few rules to fallow to be able to adjust display to fit on the screen.
Experiement with your containers. Most times try to avoid Canvas or absolute layout, and use auto-layout containers width and height set to 100%.
I'm not saying never use Canvas or absolute positioning, they are very useful in many circumstances auto-layout is the way to go. Constraint based layout can also help.
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Greg Lafrance - Flex 2 and 3 ACE certified
Flex / AIR Development, Training, and Support Services