[Android] RecyclerView getPosition()

RecyclerView getPosition()

새로운 지원 라이브러리 버전 (22.x)부터

RecyclerView.ViewHolder 클래스의 getPostion()이 deprecated 되었고

getLayoutPosition, getAdapterPosition

메소드가 추가되었다

그러나 getAdapterPosition 이 -1 을 반환할 때가 있다

RecyclerView.NO_POSITION 인지를 꼭 확인토록 하자

if(getAdapterPosition() != RecyclerView.NO_POSITION)

+

onCreateViewHolder 에서는 새로운 인스턴스만 반환하자

(항상 new Holder()를 반환토록)

getAdapterPosition vs getLayoutPosition

둘 중 내 로직에 맞는 메소드를 고르려 구글링을 하는 도중

이런 글을 발견했다

[stack overflow]

This is a tricky situation, sorry that docs are not sufficient.

When adapter contents change (and you call notify***()) RecyclerView requests a new layout. From that moment, until layout system decides to calculate a new layout (<16 ms), the layout position and adapter position may not match because layout has not reflected adapter changes yet.

In your use case, since your data is related to your adapter contents (and I assume that data is changed at the same time with adapter changes), you should be using adapterPosition.

Be careful though, if you are calling notifyDataSetChanged(), because it invalidates everything, RecyclerView does not know that ViewHolder's adapter position until next layout is calculated. In that case, getAdapterPosition() will return RecyclerView#NO_POSITION (-1).

But lets say if you've called notifyItemInserted(0), the getAdapterPosition() of ViewHolder which was previously at position 0 will start returning 1 immediately. So as long as you are dispatching granular notify events, you are always in good state (we know adapter position even though new layout is not calculated yet).

Another example, if you are doing something on user click, if getAdapterPosition() returns NO_POSITION, it is best to ignore that click because you don't know what user clicked (unless you have some other mechanism, e.g. stable ids to lookup the item).

Edit For When Layout Position is Good

Lets say you are using LinearLayoutManager and want to access the ViewHolder above the currently clicked item. In that case, you should use layout position to get the item above.

mRecyclerView.findViewHolderForLayoutPosition(myViewHolder.getLayoutPosition() - 1)

You have to use layout position because it matches what user is currently seeing on the screen.

음 

어렵다