Swiping by button or finger is different

[BeaumerF]

How to make the "finger swipe" changing the data list like the "buttons swipe" (on the bottom) ?

I just want to keep the last imageDecoration as first of the list (instead of last) but it gives me an error when I change:
dismissImg() or addImg(img); by:

var i = data.removeLast(); data.insert(0, i);