效果图
anglerNRD90Tzhuleiyue09212016183407.gif
RecyclerView实现加载更多可分为两个步骤
- RecyclerView滑动到底部的监听
- 给RecyclerView添加footer，展示加载状态
一、给RecyclerView添加ScrollListener监听滑动到底部
1. 继承RecyclerView添加滑动监听
public class LoadMoreRecyclerView extends RecyclerView {
public LoadMoreRecyclerView(Context context) {
this(context, null);
}
public LoadMoreRecyclerView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public LoadMoreRecyclerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
addOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
}
});
}
}
2. 判断滑动到底部
2.1 判断滑动方向
给LoadMoreRecyclerView添加属性
/**
* 是否是向下滑动
*/
private boolean isScrollDown;
在OnScrollListener中的onScrolled方法中判断RecyclerView的滑动方向
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
isScrollDown = dy > 0;
}
RecyclerView在滑动完成的时候会调用onScrolled方法，其中dx和dy分别表示水平滑动和垂直滑动的距离
如果dy>0表示向下滑动
2.2 判断滑动到底部
在OnScrollListener中的onScrollStateChanged方法中判断RecyclerView是否滑动到底部
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (newState == RecyclerView.SCROLL_STATE_IDLE) {// RecyclerView已经停止滑动
int lastVisibleItem;
// 获取RecyclerView的LayoutManager
LayoutManager layoutManager = recyclerView.getLayoutManager();
// 获取到最后一个可见的item
if (layoutManager instanceof LinearLayoutManager) {// 如果是LinearLayoutManager
lastVisibleItem = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
} else if (layoutManager instanceof StaggeredGridLayoutManager) {// 如果是StaggeredGridLayoutManager
int[] into = new int[((StaggeredGridLayoutManager) layoutManager).getSpanCount()];
((StaggeredGridLayoutManager) layoutManager).findLastVisibleItemPositions(into);
lastVisibleItem = findMax(into);
} else {// 否则抛出异常
throw new RuntimeException("Unsupported LayoutManager used");
}
// 获取item的总数
int totalItemCount = layoutManager.getItemCount();
/*
并且最后一个可见的item为最后一个item
并且是向下滑动
*/
if (lastVisibleItem >= totalItemCount - 1 && isScrollDown) {
// 此处调用加载更多回调接口的回调方法
}
}
}
/**
* 获取数组中的最大值
*
* @param lastPositions 需要找到最大值的数组
* @return 数组中的最大值
*/
private int findMax(int[] lastPositions) {
int max = lastPositions[0];
for (int value : lastPositions) {
if (value > max) {
max = value;
}
}
return max;
}
RecyclerView的滑动状态改变时会调用onScrollStateChanged方法，其中newState表示RecyclerView的滑动状态
- SCROLL_STATE_IDLE 表示RecyclerView没有在滑动
- SCROLL_STATE_DRAGGING 表示RecyclerView正在被拖着滑动
- SCROLL_STATE_SETTLING 表示RecyclerView正在滑动但是没有外部控制
3. 添加加载更多的回调接口
3.1 创建加载更多回调接口
/**
* 加载更多的回调接口
*/
public interface OnLoadMore {
void onLoad();
}
3.2 给RecyclerView添加设置回调的方法
/**
* 加载更多的回调接口
*/
private OnLoadMore mOnLoadMore;
/**
* 是否加载更多
*/
private boolean mIsLoadMore;
/**
* 设置加载更多的回调接口
* @param onLoadMore 加载更多的回调接口
*/
public void setOnLoadMore(OnLoadMore onLoadMore) {
// 是否加载更多置为true
this.mIsLoadMore = true;
this.mOnLoadMore = onLoadMore;
}
在判断滑动到底部的地方调用回调接口的回调方法
二、给RecyclerView添加footer展示加载状态
1. 继承Adapter添加footer
private static class LoadMoreAdapter extends Adapter {
/**
* 添加footer的类型
*/
private static final int TYPE_FOOTER = -1;
/**
* footer的状态
*/
protected int mLoadMoreStatus = STATUS_PREPARE;
/**
* footer的点击事件
*/
protected View.OnClickListener mListener;
/**
* 正常item的adapter
*/
private Adapter mAdapter;
/**
* 是否加载更多
*/
private boolean mIsLoadMore;
/**
* GridLayoutManager
*/
private GridLayoutManager mGridLayoutManager;
public LoadMoreAdapter(Adapter adapter, boolean isLoadMore) {
this.mAdapter = adapter;
this.mIsLoadMore = isLoadMore;
}
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
this.mGridLayoutManager = (GridLayoutManager) recyclerView.getLayoutManager();
}
}
@Override
public void onViewAttachedToWindow(ViewHolder holder) {
super.onViewAttachedToWindow(holder);
if (mIsLoadMore) {// 如果加载更多
if (mGridLayoutManager != null) {
mGridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
// 当position为最后一项时返回spanCount
return position == getItemCount() - 1 ? mGridLayoutManager.getSpanCount() : 1;
}
});
}
ViewGroup.LayoutParams params = holder.itemView.getLayoutParams();
if (params instanceof StaggeredGridLayoutManager.LayoutParams) {
if (holder.getLayoutPosition() == getItemCount() - 1) { // 当position为最后一项时这是FullSpan为true
((StaggeredGridLayoutManager.LayoutParams) params).setFullSpan(true);
}
}
}
}
/**
* 如果是footer类型,创建FooterView
* 否则创建正常的ItemView
*/
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (mIsLoadMore && viewType == TYPE_FOOTER) {
return onCreateFooterViewHolder(parent);
} else {
return mAdapter.onCreateViewHolder(parent, viewType);
}
}
/**
* 如果加载更多且是footer类型,则展示footer
* 否则展示正常的item
*/
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
if (mIsLoadMore && getItemViewType(position) == TYPE_FOOTER) {
bindFooterItem(holder);
} else {
mAdapter.onBindViewHolder(holder, position);
}
}
/**
* 如果加载更多
* 如果正常的item为0 则不显示footer,返回0
* 如果正常的item不为0 则返回mAdapter.getItemCount() + 1
* 如果不加载更多
* 返回mAdapter.getItemCount()
*/
@Override
public int getItemCount() {
return mIsLoadMore ? mAdapter.getItemCount() == 0 ? 0 : mAdapter.getItemCount() + 1 : mAdapter.getItemCount();
}
/**
* 如果加载更多且position为最有一个,则返回类型为footer
* 否则返回mAdapter.getItemViewType(position)
*/
@Override
public int getItemViewType(int position) {
if (mIsLoadMore && position == getItemCount() - 1) {
return TYPE_FOOTER;
} else {
return mAdapter.getItemViewType(position);
}
}
/**
* 设置footer的状态,并通知更改
*/
void setLoadMoreStatus(int status) {
this.mLoadMoreStatus = status;
notifyItemChanged(getItemCount() - 1);
}
/**
* 设置footer的点击重试事件
* @param listener
*/
public void setRetryListener(View.OnClickListener listener) {
this.mListener = listener;
}
public int getLoadMoreStatus() {
return this.mLoadMoreStatus;
}
/**
* 创建FooterView
*/
public ViewHolder onCreateFooterViewHolder(ViewGroup parent) {
return new FooterViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.footer_view_sample, parent, false));
}
/**
* 设置是否加载更多
*/
public void setIsLoadMore(boolean isLoadMore) {
this.mIsLoadMore = isLoadMore;
}
/**
* 展示FooterView
* @param holder
*/
protected void bindFooterItem(ViewHolder holder) {
FooterViewHolder footerViewHolder = (FooterViewHolder) holder;
switch (mLoadMoreStatus) {
case STATUS_LOADING:
holder.itemView.setVisibility(View.VISIBLE);
footerViewHolder.pb.setVisibility(View.VISIBLE);
footerViewHolder.tv.setText("正在加载更多...");
break;
case STATUS_EMPTY:
holder.itemView.setVisibility(View.VISIBLE);
footerViewHolder.pb.setVisibility(View.GONE);
footerViewHolder.tv.setText("没有更多了");
holder.itemView.setOnClickListener(null);
break;
case STATUS_ERROR:
holder.itemView.setVisibility(View.VISIBLE);
footerViewHolder.pb.setVisibility(View.GONE);
footerViewHolder.tv.setText("加载出错，点击重试");
holder.itemView.setOnClickListener(mListener);
break;
case STATUS_PREPARE:
holder.itemView.setVisibility(View.INVISIBLE);
break;
case STATUS_DISMISS:
holder.itemView.setVisibility(GONE);
}
}
}
static class FooterViewHolder extends RecyclerView.ViewHolder {
ProgressBar pb;
TextView tv;
public FooterViewHolder(View itemView) {
super(itemView);
pb = (ProgressBar) itemView.findViewById(R.id.pb_footer_view);
tv = (TextView) itemView.findViewById(R.id.tv_footer_view);
}
}
footer_view_sample.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:orientation="horizontal"
android:padding="16dp">
<ProgressBar
android:id="@+id/pb_footer_view"
style="@android:style/Widget.ProgressBar.Small"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tv_footer_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="8dp"
android:gravity="center"
android:text="正在加载更多..." />
</LinearLayout>
2. 设置在GridLayoutManager和StaggeredGridLayoutManager下footer撑满一行
2.1 GridLayoutManager
重写Adapter的onAttachedToRecyclerView，获取GridLayoutManager
/**
* GridLayoutManager
*/
private GridLayoutManager mGridLayoutManager;
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
this.mGridLayoutManager = (GridLayoutManager) recyclerView.getLayoutManager();
}
}
重写onViewAttachedToWindow，给GridLayoutManager设置SpanSizeLookup
@Override
public void onViewAttachedToWindow(ViewHolder holder) {
super.onViewAttachedToWindow(holder);
if (mIsLoadMore) {// 如果加载更多
if (mGridLayoutManager != null) {
mGridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
// 当position为最后一项时返回spanCount
return position == getItemCount() - 1 ? mGridLayoutManager.getSpanCount() : 1;
}
});
}
}
}
2.2 StaggeredGridLayoutManager
重写onViewAttachedToWindow
@Override
public void onViewAttachedToWindow(ViewHolder holder) {
super.onViewAttachedToWindow(holder);
if (mIsLoadMore) {// 如果加载更多
ViewGroup.LayoutParams params = holder.itemView.getLayoutParams();
if (params instanceof StaggeredGridLayoutManager.LayoutParams) {
if (holder.getLayoutPosition() == getItemCount() - 1) { // 当position为最后一项时这是FullSpan为true
((StaggeredGridLayoutManager.LayoutParams) params).setFullSpan(true);
}
}
}
}
2. 在LoadMoreRecyclerView的滑动监听中添加判断并设置footer状态
private void init() {
addOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (mOnLoadMore != null) {// 如果加载更多的回调接口不为空
if (newState == RecyclerView.SCROLL_STATE_IDLE) {// RecyclerView已经停止滑动
...
/*
如果RecyclerView的footer的状态为准备中
并且最后一个可见的item为最后一个item
并且是向下滑动
*/
if (mLoadMoreAdapter.getLoadMoreStatus() == STATUS_PREPARE
&& lastVisibleItem >= totalItemCount - 1 && isScrollDown) {
// 设置RecyclerView的footer的状态为加载中
mLoadMoreAdapter.setLoadMoreStatus(STATUS_LOADING);
// 触发加载更多的回调方法
mOnLoadMore.onLoad();
}
}
}
}
...
});
}
3. 在LoadMoreRecyclerView中重写setAdapter方法，设置footer状态和点击事件
private LoadMoreAdapter mLoadMoreAdapter;
public void setAdapter(Adapter adapter) {
this.mLoadMoreAdapter = new LoadMoreAdapter(adapter, mIsLoadMore);
this.mLoadMoreAdapter.setRetryListener(retryListener);
super.setAdapter(mLoadMoreAdapter);
}
/**
* 设置footer的状态
*/
public void setLoadMoreStatus(int status) {
if (mLoadMoreAdapter != null) {
mLoadMoreAdapter.setLoadMoreStatus(status);
}
}
/**
* footer的重试点击事件
*/
View.OnClickListener retryListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
mLoadMoreAdapter.setLoadMoreStatus(STATUS_LOADING);
mOnLoadMore.onLoad();
}
};
** ps: 关于onViewAttachedToWindow和onViewAttachedToWindow的说明 **
onViewAttachedToWindow方法在RecyclerView调用setAdapter方法是被调用
-
onViewAttachedToWindow方法在RecyclerView展示在界面上是被调用
** 为了保证LoadMoreRecyclerView中setOnLoadMore和setAdapter调用的无序性，不能在onViewAttachedToWindow方法中设置GridLayoutManager的SpanSizeLookup **
三、使用注意
** 因为重写了RecyclerView的setAdapter方法，把传如的adapter包装之后重新设置，所以在调用notifyDataSetChanged()等方法时，不能直接用自己创建adapter调用，而要使用RecyclerView.getAdapter调用。**
