老規矩，先上效果圖。

1 判斷到達底部

首先思考下自動載入更多這個需求，可以知道就是滑動到底部的時候同時載入更多的資料。那麼首先需要做的就是判斷是否滑動到了底部。

RecyclerView 有個方法onScrolled(int dx, int dy)會在整個滑動過程呼叫，所以我們可以在這個方法中去判斷是否到達底部。

至於要怎麼判斷呢？

到達底部即是說我們的列表的最底部已經展示了最後一條資料，這一條資料的position我們是知道的，即條目總數-1。

如果我們能獲取到滑動過程中，螢幕上顯示的最後一條的position，如果它的值等於條目總數-1的話，這個時候就說明已經滑動到最底部了。

看程式碼：

 @Override
 public void onScrolled(int dx, int dy) {
     super.onScrolled(dx, dy);
     //拿到最後一條的position
     int endCompletelyPosition = getLayoutManager().
     findLastCompletelyVisibleItemPosition();
     if (endCompletelyPosition ==getAdapter().getItemCount()-1){
         //執行載入更多的方法，無論是用介面還是別的方式都行
 

     }
 }

我這兒是重寫的RecyclerView,如果不想重寫，也可以用RecyclerView的addOnScrollListener方法，都差不多的。

2 新增底部的View

大多數情況下，我們載入更多的或者下拉重新整理的時候，都要有提示才合理。用ListView的話，可以直接用addFooterView方法，但是RecyclerView沒有這個方法，該怎麼辦呢。

這裡有一種方法是根據itemType來判斷，如果是最後一條，就新增的是底部View，其餘的是正常的View。

需要重寫Adapter 裡面的 getItemViewType(int position) 方法。

    @Override
    public int getItemViewType(int position) {
        if (position == getItemCount() - 1){
            return ITEM_TYPE_FOOTER;
        }else {
            return 1;
        }
    }

然後在onCreateViewHolder方法裡面，新增底部View

@Override
    public CommonRcViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == ITEM_TYPE_FOOTER){
            View view = 底部View;//可以通過layoutInflater獲取
            return new CommonRcViewHolder(view);
        }elese
        return super.onCreateViewHolder(parent, viewType);
    }

在onBindViewHolder方法中設定資料的時候也要判斷一下

@Override
public void onBindViewHolder(CommonRcViewHolder holder, int position) {
        if (getItemViewType(position) != ITEM_TYPE_FOOTER){
            //載入資料
        } 
}

大體上就是這樣了。

這裡我自己封裝了一個簡單的

LoadMoreRecyclerView.java

package cn.demo.videolist.recycler;

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.Log;

public class LoadMoreRecyclerView extends RecyclerView {

    private LinearLayoutManager mLinearLayoutManager;
    private LoadMoreAdapter mAdapter;

    public LoadMoreRecyclerView(Context context) {
        this(context,null);
    }

    public LoadMoreRecyclerView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs,0);
    }

    public LoadMoreRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

    }

    @Override
    public void onScrolled(int dx, int dy) {
        super.onScrolled(dx, dy);
        int endCompletelyPosition = mLinearLayoutManager.findLastCompletelyVisibleItemPosition();
        if (endCompletelyPosition == mAdapter.getItemCount()-1){
            mAdapter.loadMore();
        }
    }

    public void setManager(){
        mLinearLayoutManager = new LinearLayoutManager(getContext());
        setLayoutManager(mLinearLayoutManager);
    }

    public LinearLayoutManager getLayoutManager() {
        return mLinearLayoutManager;
    }

    public void setLoadMoreAdapter(LoadMoreAdapter mAdapter) {
        this.mAdapter = mAdapter;
        setAdapter(mAdapter);
    }
}

LoadMoreAdapter.java

package cn.demo.videolist.recycler;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import cn.demo.videolist.R;

public abstract class LoadMoreAdapter extends RecyclerView.Adapter<CommonRcViewHolder> {
    public static final int ITEM_TYPE_FOOTER = 0;

    protected String loadMoreText = "載入更多";


    @Override
    public int getItemViewType(int position) {
        if (position == getItemCount() - 1){
            return ITEM_TYPE_FOOTER;
        }else {
            return 1;
        }
    }

    @Override
    public CommonRcViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == ITEM_TYPE_FOOTER){
            View view = LayoutInflater.from(parent.getContext()).inflate(getFooterViewResId(),parent,false);
            return new CommonRcViewHolder(view);
        }else {
            return getViewHolder(parent,viewType);
        }
    }

    @Override
    public void onBindViewHolder(CommonRcViewHolder holder, int position) {
        if (getItemViewType(position) != ITEM_TYPE_FOOTER){
            loadData(holder, position);
        }else {
            TextView tv = holder.getView(getFooterTextViewResId());
            tv.setText(loadMoreText);
        }
    }

    @Override
    public int getItemCount() {
        return getCount()+1;
    }

    public void setLoadMoreText(String loadMoreText) {
        this.loadMoreText = loadMoreText;
        notifyItemChanged(getItemCount()-1);
    }

    public abstract int getFooterViewResId();
    public abstract int getFooterTextViewResId();
    public abstract int getCount();
    public abstract CommonRcViewHolder getViewHolder(ViewGroup parent, int viewType);
    public abstract void loadData(CommonRcViewHolder holder, int position);
    public abstract void loadMore();
}

上面用到的一個通用的ViewHolder,當然也可以自己換別的ViewHolder,畢竟我這兒沒把點選做進去

CommonRcViewHolder.java

package cn.demo.videolist.recycler;

import android.support.v7.widget.RecyclerView;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class CommonRcViewHolder extends RecyclerView.ViewHolder {

    private SparseArray<View> views = new SparseArray<>();
    private View view;
    public CommonRcViewHolder(View itemView ) {
        super(itemView);
        view = itemView;
    }

    public <T extends View> T getView(int viewId){
        View v = views.get(viewId);

        if (v==null){
            v = view.findViewById(viewId);
            views.put(viewId, v);
        }
        return (T)v;
    }

    public <T extends View> T getViewWithLayoutParams(int viewId,ViewGroup.LayoutParams lp){
        View v = views.get(viewId);

        if (v==null){
            v = view.findViewById(viewId);
            v.setLayoutParams(lp);
            views.put(viewId,v);
        }
        return (T)v;
    }

    public CommonRcViewHolder setText(int viewId,String text){
        TextView tv = getView(viewId);
        tv.setText(text);
        return this;
    }
}

用法也很簡單，關鍵的幾步有

recyclerView = (LoadMoreRecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setManager();
        final Adapter adapter = new Adapter();
        recyclerView.setLoadMoreAdapter(adapter);

重寫的Adapter要繼承自上面的LoadMoreAdapter

Adapter

      class Adapter extends LoadMoreAdapter{

        private LinkedList<String> mData;

        public Adapter( ) {
            mData = new LinkedList<>();
            for (int i = 0; i < 20; i++) {
                mData.add("item "+i+"");
            }
        }

        public void addDate(){
            for (int i = 0; i < 3; i++) {
                mData.addFirst("refresh "+i);
            }
            recyclerView.getLayoutManager().scrollToPosition(0);
            notifyItemRangeInserted(0,3);
        }

        @Override
        public CommonRcViewHolder getViewHolder(ViewGroup parent, int viewType) {
            View view = getLayoutInflater().inflate(R.layout.item_recycler, parent,false);
            return new CommonRcViewHolder(view);
        }

        @Override
        public void loadData(CommonRcViewHolder holder, int position) {
            TextView tv = holder.getView(R.id.tv);
            tv.setText(mData.get(position));
        }

        @Override
        public void loadMore() {
            int startPosition = getCount();
            if (mData.size() < 100) {
                for (int i = 0; i < 20; i++) {
                    mData.add("more "+i + "");
                }
                int endPosition = getCount()-1;
                notifyItemRangeInserted(startPosition,20);
            }else {
                setLoadMoreText("沒有更多了");
            }
        }

        @Override
        public int getFooterViewResId() {
            return R.layout.item_footer;
        }

        @Override
        public int getFooterTextViewResId() {
            return R.id.tv;
        }

        @Override
        public int getCount() {
            return mData.size();
        }

    }

兩個item檔案

item_recycler.xml

<?xml version="1.0" encoding="utf-8"?>
<TextView android:textSize="20sp"
    android:textStyle="bold"
    android:gravity="center"
    android:id="@+id/tv"
    android:textColor="#ffffff"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    xmlns:android="http://schemas.android.com/apk/res/android" />

item_footer.xml

<?xml version="1.0" encoding="utf-8"?>
<TextView android:text="載入更多"
    android:textSize="20sp"
    android:textStyle="bold"
    android:gravity="center"
    android:id="@+id/tv"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    xmlns:android="http://schemas.android.com/apk/res/android" />