How to detect when user have scrolled to the top m

问题:

I have tried writing the following code

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
  super.onScrolled(recyclerView, dx, dy);
  if(dy > 0){
    //scrolling up
  } else {
    //scrolling down
    int pastVisibleItems = linearLayoutManager.findFirstVisibleItemPosition();
    if (pastVisibleItems  == 0) {
      Toast.makeText(getContext(),"Top most item",Toast.LENGTH_SHORT).show();
    }
  }
}

but it doesn't work. I have also tried using the android's SwipeRefreshLayout to do this since it does what I want which is able to detect when user has scroll to the topmost item. I decided to not use it because I can't seem to prevent the loading indicator from popping out (I don't want to see the loading indicator come out at all).

So, basically what I want to do is:

1. check user scrolling
2. is it the topmost item already?
3. if yes, execute something, if no then nothing

Any idea how to accomplish this?

Thanks.

回答1:

Replace your code with below code:

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
  super.onScrolled(recyclerView, dx, dy);

  int pastVisibleItems = linearLayoutManager.findFirstCompletelyVisibleItemPosition();
  if (pastVisibleItems  == 0) {
    Toast.makeText(getContext(),"Top most item",Toast.LENGTH_SHORT).show();                
  }
}

it works for me, if you get any error then comment.

回答2:

I have solved my question by myself. I used the code below instead

private boolean isUserScrolling = false;
private boolean isListGoingUp = true;

Then in the RecyclerView OnScrollListener

@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
    super.onScrollStateChanged(recyclerView, newState);
    //detect is the topmost item visible and is user scrolling? if true then only execute
    if(newState ==  RecyclerView.SCROLL_STATE_DRAGGING){
        isUserScrolling = true;
        if(isListGoingUp){
            //my recycler view is actually inverted so I have to write this condition instead
            if(linearLayoutManager.findLastCompletelyVisibleItemPosition() + 1 == list.size()){
                Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        if(isListGoingUp) {
                            if (linearLayoutManager.findLastCompletelyVisibleItemPosition() + 1 == list.size()) {
                                Toast.makeText(getContext(),"exeute something", Toast.LENGTH_SHORT).show();
                            }
                        }
                    }
                },50);
                //waiting for 50ms because when scrolling down from top, the variable isListGoingUp is still true until the onScrolled method is executed
            }
        }
    }
}

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);
    if(isUserScrolling){
        if(dy > 0){
            //means user finger is moving up but the list is going down
            isListGoingUp = false;
        }
        else{
            //means user finger is moving down but the list is going up
            isListGoingUp = true;
        }
    }
}

回答3:

You Can Do This easily use Code

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);

        if(newState ==  RecyclerView.SCROLL_STATE_DRAGGING) {
            isUserScrolling = true;
        }
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {

        super.onScrolled(recyclerView, dx, dy);

        if(isUserScrolling){
            if(dy > 0){
               //Scroll list Down
            }
            else{
                if(!recyclerView.canScrollVertically(-1)){

                  //This Your Top View do Something
                }
            }
        }
    }
});