how to implement pagination in RecyclerView on scroll

问题

recyclerview comes with its own scroll listener having below methods :

void    onScrollStateChanged(RecyclerView recyclerView, int newState)

Callback method to be invoked when RecyclerView's scroll state changes.

void    onScrolled(RecyclerView recyclerView, int dx, int dy)

Callback method to be invoked when the RecyclerView has been scrolled.

Is there any way to trigger loader to load more data when scroll reaches end of the list?

I have implemented this way:

@Override
public void onBindViewHolder(ViewHolder viewHolder, int i) {
    GenerItem generItem=generItems.get(i);
    Log.d("TAG","position "+i);
    if(i==generItems.size()-1)
    ((GenerSearchActivity)mContext).onScroll(i);
    viewHolder.bindValues(generItem);
}

here onScroll() in activity will trigger the loader to load more data. What is the best way please suggest.

回答1:

Here's a scroll listener which implements load more and quick return pattern:

public abstract class HidingScrollListener extends RecyclerView.OnScrollListener {

    private static final float  HIDE_THRESHOLD   = 10;
    private static final float  SHOW_THRESHOLD   = 70;

    private int                 mToolbarOffset   = 0;
    private boolean             mControlsVisible = true;
    private int                 mToolbarHeight;
    private int                 mTotalScrolledDistance;
    private int                 previousTotal    = 0;
    private boolean             loading          = true;
    private int                 visibleThreshold = 4;
    int                         firstVisibleItem, visibleItemCount, totalItemCount;
    private LinearLayoutManager layoutManager;

    public HidingScrollListener(Context context, LinearLayoutManager layoutManager) {
        mToolbarHeight = Tools.getFooterHeight(context);
        this.layoutManager = layoutManager;
    }

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

        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
            if (mTotalScrolledDistance < mToolbarHeight) {
                setVisible();
            }
            else {
                if (mControlsVisible) {
                    if (mToolbarOffset > HIDE_THRESHOLD) {
                        setInvisible();
                    }
                    else {
                        setVisible();
                    }
                }
                else {
                    if ((mToolbarHeight - mToolbarOffset) > SHOW_THRESHOLD) {
                        setVisible();
                    }
                    else {
                        setInvisible();
                    }
                }
            }
        }

    }

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

        clipToolbarOffset();
        onMoved(mToolbarOffset);

        if ((mToolbarOffset < mToolbarHeight && dy > 0) || (mToolbarOffset > 0 && dy < 0)) {
            mToolbarOffset += dy;
        }
        if (mTotalScrolledDistance < 0) {
            mTotalScrolledDistance = 0;
        }
        else {
            mTotalScrolledDistance += dy;
        }
        // for load more
        visibleItemCount = recyclerView.getChildCount();
        totalItemCount = layoutManager.getItemCount();
        firstVisibleItem = layoutManager.findFirstVisibleItemPosition();

        if (loading) {
            if (totalItemCount > previousTotal) {
                loading = false;
                previousTotal = totalItemCount;
            }
        }
        if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
            // End has been reached
            // Do something

            loading = true;
            onLoadMore();
        }
    }

    private void clipToolbarOffset() {
        if (mToolbarOffset > mToolbarHeight) {
            mToolbarOffset = mToolbarHeight;
        }
        else if (mToolbarOffset < 0) {
            mToolbarOffset = 0;
        }
    }

    private void setVisible() {
        if (mToolbarOffset > 0) {
            onShow();
            mToolbarOffset = 0;
        }
        mControlsVisible = true;
    }

    private void setInvisible() {
        if (mToolbarOffset < mToolbarHeight) {
            onHide();
            mToolbarOffset = mToolbarHeight;
        }
        mControlsVisible = false;
    }

    public abstract void onMoved(int distance);

    public abstract void onShow();

    public abstract void onHide();

    public abstract void onLoadMore();
}

And it's implementation is below:

HidingScrollListener scrollListener = new HidingScrollListener(activity, manager) {
         @Override
         public void onMoved(int distance) {

         }

         @Override
         public void onShow() {

         }

         @Override
         public void onHide() {

         }

         @Override
         public void onLoadMore() {
            // you can do your pagination here.
         }
      };
      mRecyclerView.addOnScrollListener(scrollListener);

来源：https://stackoverflow.com/questions/32955146/how-to-implement-pagination-in-recyclerview-on-scroll