Scrolling Button On Scroll View with Middle Button Selected

Please guide me on how can I create a dynamic button a scroll view that will be scrollable,开发者_如何学Python with the middle button always selected.

like this

b1    b2   b3   b4   b5(selected)     b6   b7   b8     b9

if user select b4 it should seems like that

      b1   b2   b3   b4(selected)     b5   b6   b7     b8

b2   b3   b4   b5    b6(selected)   b7   b8     b9

the way should like that. Please guide.