I found when I set focus mode to "FOCUS_MODE_CONTINUOUSAUTO" on Samsung S2, the setFocusMode method returns TRUE.
But it is infact not working! The camera video is very blurry, it is very obvious that continuous auto focus is not working!
Touch to auto focus does work, but after triggering auto focus, when I set the focus mode back to "FOCUS_MODE_CONTINUOUSAUTO", it becomes blurry again!
I think Samsung S2 does support continuous auto focus, or if it doesn't, at least QCAR should tell me the continuous auto focus mode is not supported, then I can use touch to auto focus.