[Android] RecyclerView last position listener

https://guides.codepath.com/android/Endless-Scrolling-with-AdapterViews-and-RecyclerView

위 URL을 가보시면 ListView와 GridView 그리고 RecyclerView에서 Last Position을 알아보는 소스가 공유 되어 있습니다.

아래 2016년 1월 버전보다 업데이트가 된 내용이라 공유 해드립니다.

(참고로 이전 버전은 ScrollListener를 초기화 하는데 문제가 있었습니다.)

아래 소스는 RecyclerView에 적용 할 수 있는 소스 입니다.

public abstract class EndlessRecyclerViewScrollListener extends RecyclerView.OnScrollListener {
    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 5;
    // The current offset index of data you have loaded
    private int currentPage = 0;
    // The total number of items in the dataset after the last load
    private int previousTotalItemCount = 0;
    // True if we are still waiting for the last set of data to load.
    private boolean loading = true;
    // Sets the starting page index
    private int startingPageIndex = 0;

    RecyclerView.LayoutManager mLayoutManager;

    public EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager) {
        this.mLayoutManager = layoutManager;
    }

    public EndlessRecyclerViewScrollListener(GridLayoutManager layoutManager) {
        this.mLayoutManager = layoutManager;
        visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
    }

    public EndlessRecyclerViewScrollListener(StaggeredGridLayoutManager layoutManager) {
        this.mLayoutManager = layoutManager;
        visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
    }

    public int getLastVisibleItem(int[] lastVisibleItemPositions) {
        int maxSize = 0;
        for (int i = 0; i < lastVisibleItemPositions.length; i++) {
            if (i == 0) {
                maxSize = lastVisibleItemPositions[i];
            }
            else if (lastVisibleItemPositions[i] > maxSize) {
                maxSize = lastVisibleItemPositions[i];
            }
        }
        return maxSize;
    }

    // This happens many times a second during a scroll, so be wary of the code you place here.
    // We are given a few useful parameters to help us work out if we need to load some more data,
    // but first we check if we are waiting for the previous load to finish.
    @Override
    public void onScrolled(RecyclerView view, int dx, int dy) {
        int lastVisibleItemPosition = 0;
        int totalItemCount = mLayoutManager.getItemCount();

        if (mLayoutManager instanceof StaggeredGridLayoutManager) {
            int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) mLayoutManager).findLastVisibleItemPositions(null);
            // get maximum element within the list
            lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions);
        } else if (mLayoutManager instanceof GridLayoutManager) {
            lastVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findLastVisibleItemPosition();
        } else if (mLayoutManager instanceof LinearLayoutManager) {
            lastVisibleItemPosition = ((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
        } 

        // If the total item count is zero and the previous isn't, assume the
        // list is invalidated and should be reset back to initial state
        if (totalItemCount < previousTotalItemCount) {
            this.currentPage = this.startingPageIndex;
            this.previousTotalItemCount = totalItemCount;
            if (totalItemCount == 0) {
                this.loading = true;
            }
        }
        // If it’s still loading, we check to see if the dataset count has
        // changed, if so we conclude it has finished loading and update the current page
        // number and total item count.
        if (loading && (totalItemCount > previousTotalItemCount)) {
            loading = false;
            previousTotalItemCount = totalItemCount;
        }

        // If it isn’t currently loading, we check to see if we have breached
        // the visibleThreshold and need to reload more data.
        // If we do need to reload some more data, we execute onLoadMore to fetch the data.
        // threshold should reflect how many total columns there are too
        if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
            currentPage++;
            onLoadMore(currentPage, totalItemCount, view);
            loading = true;
        }
    }
    
    // Call this method whenever performing new searches
    public void resetState() {
        this.currentPage = this.startingPageIndex;
        this.previousTotalItemCount = 0;
        this.loading = true;
    }

    // Defines the process for actually loading more data based on page
    public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);

}

https://gist.github.com/nesquena/d09dc68ff07e845cc622

현재 2016년 11월 16일 사용해봤을 때 문제 없이 잘 돌아 갑니다.

참고하세요.

=========================== 2016년 1월 버전 ==============================

RecyclerView를 사용할 때, 마지막 포지션에 위치했는지 파악하는 좋은 리스너가 있어서 공유 드립니다.

https://gist.github.com/mipreamble/b6d4b3d65b0b4775a22e

/**
* Custom Scroll listener for RecyclerView.
* Based on implementation https://gist.github.com/ssinss/e06f12ef66c51252563e
*/
public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
    public static String TAG = "EndlessScrollListener";

    private int previousTotal = 0; // The total number of items in the dataset after the last load
    private boolean loading = true; // True if we are still waiting for the last set of data to load.
    private int visibleThreshold = 5; // The minimum amount of items to have below your current scroll position before loading more.
    int firstVisibleItem, visibleItemCount, totalItemCount;

    private int currentPage = 1;

    RecyclerViewPositionHelper mRecyclerViewHelper;

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        mRecyclerViewHelper = RecyclerViewPositionHelper.createHelper(recyclerView);
        visibleItemCount = recyclerView.getChildCount();
        totalItemCount = mRecyclerViewHelper.getItemCount();
        firstVisibleItem = mRecyclerViewHelper.findFirstVisibleItemPosition();

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

            onLoadMore(currentPage);

            loading = true;
        }
    }

    //Start loading
    public abstract void onLoadMore(int currentPage); 

}

/**
* RecyclerView position helper class for any LayoutManager.
* 
* compile 'com.android.support:recyclerview-v7:22.0.0'
*/

import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class RecyclerViewPositionHelper {

    final RecyclerView recyclerView;
    final RecyclerView.LayoutManager layoutManager;

    RecyclerViewPositionHelper(RecyclerView recyclerView) {
        this.recyclerView = recyclerView;
        this.layoutManager = recyclerView.getLayoutManager();
    }

    public static RecyclerViewPositionHelper createHelper(RecyclerView recyclerView) {
        if (recyclerView == null) {
            throw new NullPointerException("Recycler View is null");
        }
        return new RecyclerViewPositionHelper(recyclerView);
    }

    /**
     * Returns the adapter item count.
     *
     * @return The total number on items in a layout manager
     */
    public int getItemCount() {
        return layoutManager == null ? 0 : layoutManager.getItemCount();
    }

    /**
     * Returns the adapter position of the first visible view. This position does not include
     * adapter changes that were dispatched after the last layout pass.
     *
     * @return The adapter position of the first visible item or {@link RecyclerView#NO_POSITION} if
     * there aren't any visible items.
     */
    public int findFirstVisibleItemPosition() {
        final View child = findOneVisibleChild(0, layoutManager.getChildCount(), false, true);
        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
    }

    /**
     * Returns the adapter position of the first fully visible view. This position does not include
     * adapter changes that were dispatched after the last layout pass.
     *
     * @return The adapter position of the first fully visible item or
     * {@link RecyclerView#NO_POSITION} if there aren't any visible items.
     */
    public int findFirstCompletelyVisibleItemPosition() {
        final View child = findOneVisibleChild(0, layoutManager.getChildCount(), true, false);
        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
    }

    /**
     * Returns the adapter position of the last visible view. This position does not include
     * adapter changes that were dispatched after the last layout pass.
     *
     * @return The adapter position of the last visible view or {@link RecyclerView#NO_POSITION} if
     * there aren't any visible items
     */
    public int findLastVisibleItemPosition() {
        final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, false, true);
        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
    }

    /**
     * Returns the adapter position of the last fully visible view. This position does not include
     * adapter changes that were dispatched after the last layout pass.
     *
     * @return The adapter position of the last fully visible view or
     * {@link RecyclerView#NO_POSITION} if there aren't any visible items.
     */
    public int findLastCompletelyVisibleItemPosition() {
        final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, true, false);
        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
    }

    View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
                             boolean acceptPartiallyVisible) {
        OrientationHelper helper;
        if (layoutManager.canScrollVertically()) {
            helper = OrientationHelper.createVerticalHelper(layoutManager);
        } else {
            helper = OrientationHelper.createHorizontalHelper(layoutManager);
        }

        final int start = helper.getStartAfterPadding();
        final int end = helper.getEndAfterPadding();
        final int next = toIndex > fromIndex ? 1 : -1;
        View partiallyVisible = null;
        for (int i = fromIndex; i != toIndex; i += next) {
            final View child = layoutManager.getChildAt(i);
            final int childStart = helper.getDecoratedStart(child);
            final int childEnd = helper.getDecoratedEnd(child);
            if (childStart < end && childEnd > start) {
                if (completelyVisible) {
                    if (childStart >= start && childEnd <= end) {
                        return child;
                    } else if (acceptPartiallyVisible && partiallyVisible == null) {
                        partiallyVisible = child;
                    }
                } else {
                    return child;
                }
            }
        }
        return partiallyVisible;
    } 

}

위 두 소스만 있으면 되고, 저 리스너를 RecyclerView에 addOnScrollListener로 설정하면 됩니다.

OnLoadMore 함수로 리턴 받을 수가 있습니다.

## 여기서 잠깐!!

마지막 포지션 리스너로써도 좋지만 RecyclerViewPositionHelper 클래스가 정말 잘 만들어져 있습니다.

화면에서 처음 보이는 포지션, 마지막으로 보이는 포지션등 함수를 지원 함으로써,

어떠한 위치에 포지션이 있는지를 확인 할수 있습니다.

참고하세요.