Android5.0新特性：RecyclerView实现上拉加载更多

　　RecyclerView是Android5.0以后推出的新控件，相比于ListView可定制性更大，大有取代ListView之势。下面这篇博客主要来实现RecyclerView的上拉加载更多功能。

　　基本思路是让RecyclerView的Adapter加载两种布局，第一个布局来显示主界面，第二个布局来显示上拉加载时的提示信息，让RecyclerView监听是否滑动到最后一个item，如果是，则调用上拉刷新的逻辑，拉取远程数据，并显示第二个布局。等加载完毕时，刷新

Adapter，并隐藏第二个布局。下面分析代码。

　　要加载两种不同的布局，Adapter要重写getItemViewType方法。

　　

 @Override
    public int getItemViewType(int position) {
        if (position == dataList.size())
            return 1;
        else
            return 0;
    }

　　

onCreateViewHolder根据viewtype加载ViewHolder.

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view;
        if (viewType == 0) {
            view = LayoutInflater.from(context).inflate(R.layout.grid_redu_item, parent, false);
            return new NormalHolder(view);
        } else {
            view = LayoutInflater.from(context).inflate(R.layout.sample_common_list_footer, parent, false);
            mFooterHolder = new FooterHolder(view);
            return mFooterHolder;
        }
    }

注意getItemCount长度要加1。

 @Override
    public int getItemCount() {
        return dataList.size() + 1;
    }

NormalHolder

    class NormalHolder extends RecyclerView.ViewHolder {
        ImageView img;
        TextView name;

        public NormalHolder(View itemView) {
            super(itemView);
            img = (ImageView) itemView.findViewById(R.id.homepage_grid_picpic);
            name = (TextView) itemView.findViewById(R.id.homepage_grid_name);
        }

        public void setData(int position) {
            imageLoader.displayImage(context, imgUrls[position % imgUrls.length], img);
            name.setText(dataList.get(position));
        }
    }

　　

FooterHolder

    public class FooterHolder extends RecyclerView.ViewHolder {
        View mLoadingViewstubstub;
        View mEndViewstub;
        View mNetworkErrorViewstub;

        public FooterHolder(View itemView) {
            super(itemView);
            mLoadingViewstubstub = itemView.findViewById(R.id.loading_viewstub);
            mEndViewstub = itemView.findViewById(R.id.end_viewstub);
            mNetworkErrorViewstub = itemView.findViewById(R.id.network_error_viewstub);
        }

        //根据传过来的status控制哪个状态可见
        public void setData(LoadingFooter.FooterState status) {
            Log.d("TAG", "reduAdapter" + status + "");
            switch (status) {
                case Normal:
                    setAllGone();
                    break;
                case Loading:
                    setAllGone();
                    mLoadingViewstubstub.setVisibility(View.VISIBLE);
                    break;
                case TheEnd:
                    setAllGone();
                    mEndViewstub.setVisibility(View.VISIBLE);
                    break;
                case NetWorkError:
                    setAllGone();
                    mNetworkErrorViewstub.setVisibility(View.VISIBLE);
                    break;
                default:
                    break;
            }

        }

        //全部不可见
        void setAllGone() {
            if (mLoadingViewstubstub != null) {
                mLoadingViewstubstub.setVisibility(View.GONE);
            }
            if (mEndViewstub != null) {
                mEndViewstub.setVisibility(View.GONE);
            }
            if (mNetworkErrorViewstub != null) {
                mNetworkErrorViewstub.setVisibility(View.GONE);
            }
        }

    }

　　

　　FooterHolder布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/loading_view"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:gravity="center"
    android:orientation="vertical"
    tools:layout_height="wrap_content">

    <include
        android:id="@+id/loading_viewstub"
        layout="@layout/sample_common_list_footer_loading"
        android:layout_width="match_parent"
        android:layout_height="40dp" />

    <include
        android:id="@+id/end_viewstub"
        layout="@layout/sample_common_list_footer_end"
        android:layout_width="match_parent"
        android:layout_height="40dp" />

    <include
        android:id="@+id/network_error_viewstub"
        layout="@layout/sample_common_list_footer_network_error"
        android:layout_width="match_parent"
        android:layout_height="40dp" />
</LinearLayout>

　　显示效果：

 

　　主要逻辑放在Fragment里。
　　首先我们要绑定为RecyclerView绑定一个监听器，监听RecyclerView是否滑到了底部。
　　Listener代码：
　　

package com.yctime.truelove.LoadMore;

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 android.view.View;

import com.yctime.truelove.ImageLoader.UILPauseOnScrollListener;

/**
 * Created by xjx
 * <p/>
 * 继承自RecyclerView.OnScrollListener，一：可以监听到是否滑动到页面最低部。二：滑动时停止加载图片
 */
public class EndlessRecyclerOnScrollListener extends UILPauseOnScrollListener {

    /**
     * 当前RecyclerView类型
     */
    protected LayoutManagerType 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;

    /**
     * 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();

        if (layoutManagerType == null) {
            if (layoutManager instanceof LinearLayoutManager) {
                layoutManagerType = LayoutManagerType.LinearLayout;
            } else if (layoutManager instanceof GridLayoutManager) {
                layoutManagerType = LayoutManagerType.GridLayout;
            } else if (layoutManager instanceof StaggeredGridLayoutManager) {
                layoutManagerType = LayoutManagerType.StaggeredGridLayout;
            } else {
                throw new RuntimeException(
                        "Unsupported LayoutManager used. Valid ones are LinearLayoutManager, GridLayoutManager and StaggeredGridLayoutManager");
            }
        }

        switch (layoutManagerType) {
            case LinearLayout:
                lastVisibleItemPosition = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
                break;
            case GridLayout:
                lastVisibleItemPosition = ((GridLayoutManager) layoutManager).findLastVisibleItemPosition();
                break;
            case StaggeredGridLayout:
                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)) {
            onLoadNextPage(recyclerView);
        }
    }

    /**
     * 取数组中最大值
     *
     * @param lastPositions
     * @return
     */
    private int findMax(int[] lastPositions) {
        int max = lastPositions[0];
        for (int value : lastPositions) {
            if (value > max) {
                max = value;
            }
        }

        return max;
    }

    public void onLoadNextPage(final View view) {
    }

    public static enum LayoutManagerType {
        LinearLayout,
        StaggeredGridLayout,
        GridLayout
    }
}

 下面是Fragment完整代码：

package com.yctime.truelove.fragment;


import android.support.v4.app.Fragment;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;

import com.yctime.truelove.LoadMore.EndlessRecyclerOnScrollListener;
import com.yctime.truelove.LoadMore.LoadingFooter;
import com.yctime.truelove.MainActivity;
import com.yctime.truelove.Utils.NetworkUtils;
import com.yctime.truelove.login.R;

import java.util.ArrayList;


/**
 * A simple {@link Fragment} subclass.
 */
public class HomeReDuFragment extends BaseFragment {

    private RecyclerView mRecyclerView;
    private GridAdapter_Redu gridReDuAdapter;
    // 服务器端一共多少条数据
    private static final int TOTAL_COUNTER = 50;
    // 每一页展示多少条数据
    private static final int REQUEST_COUNT = 12;
    // 已经获取到多少条数据了
    private int mCurrentCounter = 0;
    //模拟的数据源
    private ArrayList<String> dataList;


    protected LoadingFooter.FooterState mState = LoadingFooter.FooterState.Normal;

    protected void setState(LoadingFooter.FooterState mState) {
        this.mState = mState;
        ((MainActivity) mContext).runOnUiThread(new Runnable() {
            @Override
            public void run() {
                changeAdaperState();
            }
        });
    }

    //改变底部bottom的样式
    protected void changeAdaperState() {
        if (gridReDuAdapter != null && gridReDuAdapter.mFooterHolder != null) {
            gridReDuAdapter.mFooterHolder.setData(mState);
        }
    }

    public HomeReDuFragment() {
    }


    @Override
    protected View initView() {
        View mView = LayoutInflater.from(mContext).inflate(R.layout.homepage_viewpager_item_redu, null);
        mRecyclerView = (RecyclerView) mView.findViewById(R.id.home_page_recyclerview);
        return mView;
    }

    @Override
    protected void initData() {
        initGridView();
    }


    private View initGridView() {
        mRecyclerView.setHasFixedSize(true);
        //滑动暂停加载网络图片,而且可以监听recycler是否滑动到底部
        mRecyclerView.addOnScrollListener(mOnScrollListener);
        mRecyclerView.setItemAnimator(new DefaultItemAnimator());
        gridReDuAdapter = new GridAdapter_Redu(mContext);
        gridReDuAdapter.addAll(getRemoteData());
        mRecyclerView.setAdapter(gridReDuAdapter);
        GridLayoutManager layoutManager = new GridLayoutManager(mContext, 3);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        layoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int position) {
                //如果是最后一个item，则设置占据3列，否则占据1列
                boolean isFooter = position == gridReDuAdapter.getItemCount() - 1;
                return isFooter ? 3 : 1;
            }
        });
        mRecyclerView.setLayoutManager(layoutManager);
        return mRecyclerView;
    }

    private EndlessRecyclerOnScrollListener mOnScrollListener = new EndlessRecyclerOnScrollListener() {
        @Override
        public void onLoadNextPage(View view) {
            super.onLoadNextPage(view);

            if (mState == LoadingFooter.FooterState.Loading) {
                Log.d("@TAG", "the state is Loading, just wait..");
                return;
            }

            if (mCurrentCounter < TOTAL_COUNTER) {
                // loading more
                requestData();
                Log.d("TAG", "请求数据");
            } else {
                //the end
                setState(LoadingFooter.FooterState.TheEnd);
            }
        }
    };


    /**
     * 模拟请求网络
     */
    private void requestData() {
        setState(LoadingFooter.FooterState.Loading);
        new Thread() {
            @Override
            public void run() {
                super.run();
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (NetworkUtils.isNetAvailable(mContext)) {
                    //模拟请求远程数据
                    gridReDuAdapter.addAll(getRemoteData());
                    //加载完毕时
                    setState(LoadingFooter.FooterState.Normal);
                    Log.d("TAG", mCurrentCounter + "");
                } else {
                    //模拟一下网络请求失败的情况
                    setState(LoadingFooter.FooterState.NetWorkError);
                }
            }
        }.start();
    }

    //模拟请求数据
    private ArrayList<String> getRemoteData() {
        if (dataList == null)
            dataList = new ArrayList<>();
        //每次都清空一下
        dataList.clear();
        //要减去adapter最后一页
        for (int i = 0; i < REQUEST_COUNT; i++) {
            if (dataList.size() + mCurrentCounter >= TOTAL_COUNTER) {
                break;
            }
            dataList.add("账号" + (mCurrentCounter + i));
        }
        mCurrentCounter += dataList.size();
        return dataList;
    }


}

需要注意的是这个方法：

  //改变底部bottom的样式
    protected void changeAdaperState() {
        if (gridReDuAdapter != null && gridReDuAdapter.mFooterHolder != null) {
            gridReDuAdapter.mFooterHolder.setData(mState);
        }
    }

Adapter的应用调用Adapter里面的方法，来切换Adaper的样式。
　　Adapter完整代码：

package com.yctime.truelove.fragment;

import android.content.Context;
import android.content.Intent;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.yctime.truelove.ImageLoader.MyImageLoader;
import com.yctime.truelove.ImageLoader.UILImageLoader;
import com.yctime.truelove.LoadMore.LoadingFooter;
import com.yctime.truelove.drawer.MyZoneActivity;
import com.yctime.truelove.login.R;

import java.util.ArrayList;


public class GridAdapter_Redu extends RecyclerView.Adapter<RecyclerView.ViewHolder> {


    public String[] imgUrls = {
            "http://img5.duitang.com/uploads/item/201402/22/20140222113830_X3ddd.jpeg",
            "http://v1.qzone.cc/avatar/201403/01/10/36/531147afa4197738.jpg!200x200.jpg",
            "http://g.hiphotos.baidu.com/zhidao/wh%3D450%2C600/sign=e4d7ed147af40ad115b1cfe7621c3de9/b7fd5266d016092445b47837d50735fae6cd340d.jpg",
            "http://img5q.duitang.com/uploads/item/201502/19/20150219182507_vGVaK.jpeg",
            "http://p1.qqyou.com/touxiang/uploadpic/2013-3/12/2013031212190118646.jpg",
            "http://img5.duitang.com/uploads/item/201412/08/20141208221323_YVJFk.png",
            "http://cdn.duitang.com/uploads/item/201408/02/20140802222651_GWuU2.png",
            "http://ent.dzwww.com/yulezhuanti/mtcbg/201510/W020151027467479100669.jpg",
            "http://p1.qqyou.com/touxiang/uploadpic/2013-3/10/2013031009323656495.jpg",
            "http://p1.qqyou.com/touxiang/uploadpic/2013-3/12/2013031212295986807.jpg",
            "http://f.hiphotos.baidu.com/zhidao/wh%3D600%2C800/sign=10742594d739b6004d9b07b1d9601912/9f2f070828381f30ec9eabdeab014c086f06f0c5.jpg",
            "http://a.hiphotos.baidu.com/zhidao/wh%3D600%2C800/sign=5bda8a18a71ea8d38a777c02a73a1c76/5882b2b7d0a20cf4598dc37c77094b36acaf9977.jpg",
            "http://a1.att.hudong.com/36/98/300001051406133039983418031.jpg"
    };
    public Context context;
    MyImageLoader imageLoader = new UILImageLoader();
    private ArrayList<String> dataList = new ArrayList<>();


    private final int NORMALLAYOUT = 0;
    private final int FOOTERLAYOUT = 1;
    public FooterHolder mFooterHolder;

    public GridAdapter_Redu(Context context) {
        this.context = context;
    }

    public void addAll(ArrayList<String> list) {
        int lastIndex = this.dataList.size();
        if (this.dataList.addAll(list)) {
            notifyItemRangeInserted(lastIndex, list.size());
        }
    }

    @Override
    public int getItemViewType(int position) {
        if (position == dataList.size())
            return FOOTERLAYOUT;
        else
            return NORMALLAYOUT;
    }


    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view;
        if (viewType == NORMALLAYOUT) {
            view = LayoutInflater.from(context).inflate(R.layout.grid_redu_item, parent, false);
            return new NormalHolder(view);
        } else {
            view = LayoutInflater.from(context).inflate(R.layout.sample_common_list_footer, parent, false);
            mFooterHolder = new FooterHolder(view);
            return mFooterHolder;
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof NormalHolder) {
            //点击事件
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(context, MyZoneActivity.class);
                    context.startActivity(intent);
                }
            });
            ((NormalHolder) holder).setData(position);
        }
    }

    @Override
    public int getItemCount() {
        return dataList.size() + 1;
    }


    class NormalHolder extends RecyclerView.ViewHolder {
        ImageView img;
        TextView name;

        public NormalHolder(View itemView) {
            super(itemView);
            img = (ImageView) itemView.findViewById(R.id.homepage_grid_picpic);
            name = (TextView) itemView.findViewById(R.id.homepage_grid_name);
        }

        public void setData(int position) {
            imageLoader.displayImage(context, imgUrls[position % imgUrls.length], img);
            name.setText(dataList.get(position));
        }
    }

    public class FooterHolder extends RecyclerView.ViewHolder {
        View mLoadingViewstubstub;
        View mEndViewstub;
        View mNetworkErrorViewstub;

        public FooterHolder(View itemView) {
            super(itemView);
            mLoadingViewstubstub = itemView.findViewById(R.id.loading_viewstub);
            mEndViewstub = itemView.findViewById(R.id.end_viewstub);
            mNetworkErrorViewstub = itemView.findViewById(R.id.network_error_viewstub);
        }

        //根据传过来的status控制哪个状态可见
        public void setData(LoadingFooter.FooterState status) {
            Log.d("TAG", "reduAdapter" + status + "");
            switch (status) {
                case Normal:
                    setAllGone();
                    break;
                case Loading:
                    setAllGone();
                    mLoadingViewstubstub.setVisibility(View.VISIBLE);
                    break;
                case TheEnd:
                    setAllGone();
                    mEndViewstub.setVisibility(View.VISIBLE);
                    break;
                case NetWorkError:
                    setAllGone();
                    mNetworkErrorViewstub.setVisibility(View.VISIBLE);
                    break;
                default:
                    break;
            }

        }

        //全部不可见
        void setAllGone() {
            if (mLoadingViewstubstub != null) {
                mLoadingViewstubstub.setVisibility(View.GONE);
            }
            if (mEndViewstub != null) {
                mEndViewstub.setVisibility(View.GONE);
            }
            if (mNetworkErrorViewstub != null) {
                mNetworkErrorViewstub.setVisibility(View.GONE);
            }
        }

    }

}

运行效果：