I've asked a similar question about the Android ActionBar before: Change ActionBar Tabs background color
I still don't have an answer to the question: when will the two line design/when the one line design used? I've set a custom divider to my tab bar and it's also being used in the horizontal layout. However to create drawables/styles based on the orientation/screen size etc I need to know when which layout is being used. Looking through the Android source it seems they are using the same drawables for both layouts, so that doesn't really help me. The same problem applies when changing the font color of the Tab View.
I fear that it'll be decided in code which format is being used, so there's not really any way around this. Can anyone confirm this? Or is there at least a way to find out in code if the Action bar is one lined or two lined?