android - OnScrollListener for RecyclerView total scroll is inaccurate? -

i implemented onscrolllistener recyclerview follows:

new recyclerview.onscrolllistener() {     @override     public void onscrolled(recyclerview recyclerview, int dx, int dy) {         super.onscrolled(recyclerview, dx, dy);         scrolly += dy;     } }; 

this should add scroll changes scrolly holds total vertical scroll of recyclerview.

but when scroll down end of list , scroll up, scroll value not equal 0, positive (in test example ends @ around 300).

what part of implementation wrong?

okay, figured out , timing issue. might have same problem me @ point, here happened:

in fragment added onscrolllistener add dy complete scrolly value recyclerview:

new recyclerview.onscrolllistener() { @override     public void onscrolled(recyclerview recyclerview, int dx, int dy) {         super.onscrolled(recyclerview, dx, dy);         mscrolly += dy;     } }; 

in recyclerview rows, wanted use mscrolly value, whenever recyclerview scrolled, respond parallax effect, implemented onscrolllistener in viewholder, so:

new recyclerview.onscrolllistener() {     @override     public void onscrolled(recyclerview recyclerview, int dx, int dy) {         super.onscrolled(recyclerview, dx, dy);         applyparallax(mscrolly); //mscrolly calculated fragment's onscrolllistener     } }; 

i figured, since viewholders got destroyed , reused, resource efficient add child onscrolllisteners when needed.

the thing didn't know recyclerview onscrolllisteners handled in sequence of addition (it's kinda obvious after fact). since fragment's onscrolllistener added first , row's onscrolllisteners after, fragments onscrolllistener called last, resulting in mscrolly value being updated after had been handled row's onscrolllisteners, missed last update , stopped @ second last mscrolly value, positive.

i fixed implementing logic fragment's onscrolllistener (note, check first child, since needed parallax effect in first row! if have more effects in other places, must loop through current views in layoutmanager):

new recyclerview.onscrolllistener() {     @override     public void onscrolled(recyclerview recyclerview, int dx, int dy) {         super.onscrolled(recyclerview, dx, dy);         mscrolly += dy;         linearlayoutmanager manager = ((linearlayoutmanager) mrecyclerview.getlayoutmanager());         view firstchild = manager.getchildat(0);         if(firstchild.getid() == r.id.fpd_title_super){             final postdataadapter.maintitleviewholder holder = (postdataadapter.maintitleviewholder)mrecyclerview.getchildviewholder(firstchild);             holder.dispatchscrolly(mscrolly);         }     } }; 

and implementing method viewholders:

public void dispatchscrolly(int scrolly){     // handle parallax effect here } 

now works.