通过重写OnScrollListener来监听RecyclerView是否滑动到底部

为了增加复用性和灵活性，我们还是定义一个接口来做监听滚动到底部的回调，这样你就可以把它用在listview，scrollView中去。

OnBottomListener

package kale.com.waterfall;

/**
 * @author Jack Tony
 * @brief
 * @date 2015/4/6
 */
public interface OnBottomListener {
    public void onBottom();
}

接着，我们来重写RecyclerView.OnScrollListener

package kale.com.waterfall.extra.RecyclerView;

import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;

import kale.com.waterfall.OnBottomListener;

/**
 * @author Jack Tony
 * @brief recyle view 滚动监听器
 * @date 2015/4/6
 */
public class OnRcvScrollListener extends RecyclerView.OnScrollListener implements OnBottomListener {

    private String TAG = getClass().getSimpleName();

    public static enum LAYOUT_MANAGER_TYPE {
        LINEAR,
        GRID,
        STAGGERED_GRID
    }

    /**
     * layoutManager的类型（枚举）
     */
    protected LAYOUT_MANAGER_TYPE layoutManagerType;

    /**
     * 最后一个的位置
     */
    private int[] lastPositions;

    /**
     * 最后一个可见的item的位置
     */
    private int lastVisibleItemPosition;
/*    *//**
     * 是否正在加载
     *//*
    private boolean isLoadingMore = false;*/

    /**
     * 当前滑动的状态
     */
    private int currentScrollState = 0;

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

        RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        //  int lastVisibleItemPosition = -1;
        if (layoutManagerType == null) {
            if (layoutManager instanceof LinearLayoutManager) {
                layoutManagerType = LAYOUT_MANAGER_TYPE.LINEAR;
            } else if (layoutManager instanceof GridLayoutManager) {
                layoutManagerType = LAYOUT_MANAGER_TYPE.GRID;
            } else if (layoutManager instanceof StaggeredGridLayoutManager) {
                layoutManagerType = LAYOUT_MANAGER_TYPE.STAGGERED_GRID;
            } else {
                throw new RuntimeException(
                        "Unsupported LayoutManager used. Valid ones are LinearLayoutManager, GridLayoutManager and StaggeredGridLayoutManager");
            }
        }

        switch (layoutManagerType) {
            case LINEAR:
                lastVisibleItemPosition = ((LinearLayoutManager) layoutManager)
                        .findLastVisibleItemPosition();
                break;
            case GRID:
                lastVisibleItemPosition = ((GridLayoutManager) layoutManager)
                        .findLastVisibleItemPosition();
                break;
            case STAGGERED_GRID:
                StaggeredGridLayoutManager staggeredGridLayoutManager
                        = (StaggeredGridLayoutManager) layoutManager;
                if (lastPositions == null) {
                    lastPositions = new int[staggeredGridLayoutManager.getSpanCount()];
                }
                staggeredGridLayoutManager.findLastVisibleItemPositions(lastPositions);
                lastVisibleItemPosition = findMax(lastPositions);
                break;
        }

    }

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        currentScrollState = newState;
        RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        int visibleItemCount = layoutManager.getChildCount();
        int totalItemCount = layoutManager.getItemCount();
        if ((visibleItemCount > 0 && currentScrollState == RecyclerView.SCROLL_STATE_IDLE &&
                (lastVisibleItemPosition) >= totalItemCount - 1)) {
            //Log.d(TAG, "is loading more");
            onBottom();
        }
    }

    @Override
    public void onBottom() {
        //Log.d(TAG, "is onBottom");
    }

    private int findMax(int[] lastPositions) {
        int max = lastPositions[0];
        for (int value : lastPositions) {
            if (value > max) {
                max = value;
            }
        }
        return max;
    }
}

在之后的使用中，我们就可以像下方这样监听回调方法了：

waterFallRcv.setOnScrollListener(new OnRcvScrollListener(){
            @Override
            public void onBottom() {
                super.onBottom();
                // 到底部自动加载
                if (!isLoadingData){
                    Log.d(TAG, "loading old data");
                    adapter.loadOldData();
                    isLoadingData = true;
                }
            }
        });