RecyclerView实现加载更多

情景描述

我们使用列表显示数据时，通常都会遇到需要加载更多数据的情况，比如列表即将滚动到底部时，我们就需要进行新的数据的获取及填充。本篇博客介绍的是：自定义RecyclerView，添加即将滚动到底部的回调，方便实现加载更多功能。

代码

/**
* Add the callback of reaching bottom into RecyclerView
* Support three LayoutManager(Linear、Grid、StaggeredGrid)
* Created by wiky on 2016/3/26.
*/
public class RBCallbkRecyclerView extends RecyclerView {
private OnReachBottomListener onReachBottomListener;
private boolean isInTheBottom = false;
/**
* reachBottomRow = 1;(default)
* mean : when the lastVisibleRow is lastRow , call the onReachBottom();
* reachBottomRow = 2;
* mean : when the lastVisibleRow is Penultimate Row , call the onReachBottom();
* And so on
*/
private int reachBottomRow = 1;

public RBCallbkRecyclerView(Context context) {
super(context);
}

public RBCallbkRecyclerView(Context context, AttributeSet attrs) {
super(context, attrs);
}

public RBCallbkRecyclerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}

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

if (onReachBottomListener != null) {
LayoutManager layoutManager = getLayoutManager();
if (layoutManager == null) { //it maybe unnecessary
throw new RuntimeException("LayoutManager is null,Please check it!");
}
Adapter adapter = getAdapter();
if (adapter == null) { //it maybe unnecessary
throw new RuntimeException("Adapter is null,Please check it!");
}
boolean isReachBottom = false;
//is GridLayoutManager
if (layoutManager instanceof GridLayoutManager) {
GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
int rowCount = adapter.getItemCount() / gridLayoutManager.getSpanCount();
int lastVisibleRowPosition = gridLayoutManager.findLastVisibleItemPosition() / gridLayoutManager.getSpanCount();
isReachBottom = (lastVisibleRowPosition >= rowCount - reachBottomRow);
}
//is LinearLayoutManager
else if (layoutManager instanceof LinearLayoutManager) {
int lastVisibleItemPosition = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
int rowCount = adapter.getItemCount();
if (reachBottomRow > rowCount)
reachBottomRow = 1;
isReachBottom = (lastVisibleItemPosition >= rowCount - reachBottomRow);
}
//is StaggeredGridLayoutManager
else if (layoutManager instanceof StaggeredGridLayoutManager) {
StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
int spanCount = staggeredGridLayoutManager.getSpanCount();
int[] into = new int[spanCount];
int[] eachSpanListVisibleItemPosition = staggeredGridLayoutManager.findLastVisibleItemPositions(into);
for (int i = 0; i < spanCount; i++) {
if (eachSpanListVisibleItemPosition[i] > adapter.getItemCount() - reachBottomRow * spanCount) {
isReachBottom = true;
break;
}
}
}

if (!isReachBottom) {
isInTheBottom = false;
} else if (!isInTheBottom) {
onReachBottomListener.onReachBottom();
isInTheBottom = true;
Log.d("RBCallbkRecyclerView", "onReachBottom");
}
}

}

public void setReachBottomRow(int reachBottomRow) {
if (reachBottomRow < 1)
reachBottomRow = 1;
this.reachBottomRow = reachBottomRow;
}

public interface OnReachBottomListener {
void onReachBottom();
}

public void setOnReachBottomListener(OnReachBottomListener onReachBottomListener) {
this.onReachBottomListener = onReachBottomListener;
}
}

使用

基础使用和RecyclerView无差别

添加接口回调方法：

mRBCallbkRecyclerView.setOnReachBottomListener(new RBCallbkRecyclerView.OnReachBottomListener() {
@Override
public void onReachBottom() {
//即将到达几部，进行加载更多操作
}
});

同时支持设置还剩X行数据时，即进行回调

mRBCallbkRecyclerView.setReachBottomRow(1);//（默认）最后一行可见时，进行回调