LinearLayoutManager＃scrollToPositionWithOffset（）有时无法正常工作

Question

@Override
public void onResume() {
 super.onResume();
 recyclerView.post(new Runnable() {
  @Override
  public void run() {
    ((LinearLayoutManager) recyclerView.getLayoutManager()).scrollToPositionWithOffset(position, viewTopDistance);
  }
 });
}

position and viewTopDistance are saved and persisted correctly when the user clicks a view which launches another activity. Upon return to the recycler view about 2/3 of the time the list looks correct, the other 1/3 of the times it just shows the first 4 or 5 times at the top (scrollToPositionWithOffset didn't work)

Any ideas on why this fails sometimes?

Answer 1

I believe your problem is in timing. Although 'post' delays 'scrollToPositionWithOffset', the view may not be always ready. I use the following construct.

  mLstView.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    @Override
    public boolean onPreDraw() {
      if (mLstView.getChildCount() > 0) {
        recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);   
        llMgr.scrollToPositionWithOffset(position, viewTopDistance);  
        return true;
      }
      return false;
    }
  });

with success (so far). You may also look at the demo code that implements this construct (LstFrag.select).

Good Luck