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Android RecyclerView下拉刷新 & 上拉加载更多

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2017.10.23 07:24* 字数 1166
封面

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1.写在前面

本文主要实现的是上拉加载更多功能,下拉刷新使用的是Google官方的SwipeRefreshLayout控件,因为在实现这个功能的时候走了不少弯路,所以在此记录下来分享给大家,先看下效果图:

上拉加载更多

2.实现

上拉加载更多功能实际上就是给RecyclerView增加一个FooterView,然后通过判断是否滑动到了最后一条Item,来控制FooterView的显示和隐藏,接下来我们来看下如何实现:

Adapter添加FooterView

小二,上代码:

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

    private List<String> dataList;

    // 普通布局
    private final int TYPE_ITEM = 1;
    // 脚布局
    private final int TYPE_FOOTER = 2;
    // 当前加载状态,默认为加载完成
    private int loadState = 2;
    // 正在加载
    public final int LOADING = 1;
    // 加载完成
    public final int LOADING_COMPLETE = 2;
    // 加载到底
    public final int LOADING_END = 3;

    public LoadMoreAdapter(List<String> dataList) {
        this.dataList = dataList;
    }

    @Override
    public int getItemViewType(int position) {
        // 最后一个item设置为FooterView
        if (position + 1 == getItemCount()) {
            return TYPE_FOOTER;
        } else {
            return TYPE_ITEM;
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //进行判断显示类型,来创建返回不同的View
        if (viewType == TYPE_ITEM) {
            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.adapter_recyclerview, parent, false);
            return new RecyclerViewHolder(view);

        } else if (viewType == TYPE_FOOTER) {
            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.layout_refresh_footer, parent, false);
            return new FootViewHolder(view);
        }
        return null;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof RecyclerViewHolder) {
            RecyclerViewHolder recyclerViewHolder = (RecyclerViewHolder) holder;
            recyclerViewHolder.tvItem.setText(dataList.get(position));

        } else if (holder instanceof FootViewHolder) {
            FootViewHolder footViewHolder = (FootViewHolder) holder;
            switch (loadState) {
                case LOADING: // 正在加载
                    footViewHolder.pbLoading.setVisibility(View.VISIBLE);
                    footViewHolder.tvLoading.setVisibility(View.VISIBLE);
                    footViewHolder.llEnd.setVisibility(View.GONE);
                    break;

                case LOADING_COMPLETE: // 加载完成
                    footViewHolder.pbLoading.setVisibility(View.INVISIBLE);
                    footViewHolder.tvLoading.setVisibility(View.INVISIBLE);
                    footViewHolder.llEnd.setVisibility(View.GONE);
                    break;

                case LOADING_END: // 加载到底
                    footViewHolder.pbLoading.setVisibility(View.GONE);
                    footViewHolder.tvLoading.setVisibility(View.GONE);
                    footViewHolder.llEnd.setVisibility(View.VISIBLE);
                    break;

                default:
                    break;
            }
        }
    }

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

    private class RecyclerViewHolder extends RecyclerView.ViewHolder {

        TextView tvItem;

        RecyclerViewHolder(View itemView) {
            super(itemView);
            tvItem = (TextView) itemView.findViewById(R.id.tv_item);
        }
    }

    private class FootViewHolder extends RecyclerView.ViewHolder {

        ProgressBar pbLoading;
        TextView tvLoading;
        LinearLayout llEnd;

        FootViewHolder(View itemView) {
            super(itemView);
            pbLoading = (ProgressBar) itemView.findViewById(R.id.pb_loading);
            tvLoading = (TextView) itemView.findViewById(R.id.tv_loading);
            llEnd = (LinearLayout) itemView.findViewById(R.id.ll_end);
        }
    }

    /**
     * 设置上拉加载状态
     *
     * @param loadState 0.正在加载 1.加载完成 2.加载到底
     */
    public void setLoadState(int loadState) {
        this.loadState = loadState;
        notifyDataSetChanged();
    }
}

首先定义了布局和数据加载状态的一些标志,然后在getItemViewType方法中设置最后一个Item为FooterView,在onCreateViewHolder方法中根据viewType来加载不同的布局,最后在onBindViewHolder方法中设置一下加载的状态显示就OK了,对了,由于多了一个FooterView,所以要记得在getItemCount方法的返回值中加上1。

到这里一个线性布局列表的Adapter就完成了,注意,是线性布局列表(只有一列的那种),那网格布局怎么办,先看下这个Adapter在网格布局中使用会发生什么:

网格布局

可以看到加载更多的进度条显示在了一个Item上,如果想要正常显示的话,进度条需要横跨两个Item,这该怎么办呢,别担心,继续往下看:

@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
    super.onAttachedToRecyclerView(recyclerView);
    RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
    if (manager instanceof GridLayoutManager) {
        final GridLayoutManager gridManager = ((GridLayoutManager) manager);
        gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int position) {
                // 如果当前是footer的位置,那么该item占据2个单元格,正常情况下占据1个单元格
                return getItemViewType(position) == TYPE_FOOTER ? gridManager.getSpanCount() : 1;
            }
        });
    }
}

在Adapter中重写onAttachedToRecyclerView方法,首先判断当前是否为网格布局,然后给GridLayoutManager设置一个SpanSizeLookup,这是一个抽象类,里面有一个抽象方法getSpanSize,这个方法的返回值决定了每个Item占据的单元格数。

以上文为例,是一个两列的网格布局,如果当前Item是FooterView的话需要占据两个单元格才能横向充满屏幕,所以需要返回2(GridLayoutManager的getSpanCount方法获取到的是当前一行中单元格的数量),正常情况下每个Item占据一个单元格。

RecyclerView设置滑动监听

设置好FooterView之后,我们还需要判断一下什么时候显示出来,这就需要对RecyclerView设置一下滑动监听,当滑动到最后一个Item的时候,显示加载更多UI并且开始请求下一页列表的数据,看下代码:

public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {

    //用来标记是否正在向上滑动
    private boolean isSlidingUpward = false;

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        LinearLayoutManager manager = (LinearLayoutManager) recyclerView.getLayoutManager();
        // 当不滑动时
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
            //获取最后一个完全显示的itemPosition
            int lastItemPosition = manager.findLastCompletelyVisibleItemPosition();
            int itemCount = manager.getItemCount();

            // 判断是否滑动到了最后一个item,并且是向上滑动
            if (lastItemPosition == (itemCount - 1) && isSlidingUpward) {
                //加载更多
                onLoadMore();
            }
        }
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        // 大于0表示正在向上滑动,小于等于0表示停止或向下滑动
        isSlidingUpward = dy > 0;
    }

    /**
     * 加载更多回调
     */
    public abstract void onLoadMore();
}

代码中已经写了很全的注释,重点看下onScrolled这个回调方法,里面有dx、dy这两个参数,当向上滑动的时候dy是大于0的,向左滑动的时候dx是大于0的,反方向滑动则小于0,所以这段代码稍稍修改一下就可以适用于横向滑动列表的监听。

在Activity中使用

准备工作已经完成了,接下来看看如何使用吧:

public class LoadMoreActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private LoadMoreAdapter loadMoreAdapter;
    private List<String> dataList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recyclerview);

        init();
    }

    private void init() {
        recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        // 模拟获取数据
        getData();
        loadMoreAdapter = new LoadMoreAdapter(dataList);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(loadMoreAdapter);

        // 设置加载更多监听
        recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener() {
            @Override
            public void onLoadMore() {
                loadMoreAdapter.setLoadState(loadMoreAdapter.LOADING);

                if (dataList.size() < 52) {
                    // 模拟获取网络数据,延时1s
                    new Timer().schedule(new TimerTask() {
                        @Override
                        public void run() {
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    getData();
                                    loadMoreAdapter.setLoadState(loadMoreAdapter.LOADING_COMPLETE);
                                }
                            });
                        }
                    }, 1000);
                } else {
                    // 显示加载到底的提示
                    loadMoreAdapter.setLoadState(loadMoreAdapter.LOADING_END);
                }
            }
        });
    }

    private void getData() {
        char letter = 'A';
        for (int i = 0; i < 26; i++) {
            dataList.add(String.valueOf(letter));
            letter++;
        }
    }
}

调用RecyclerView的addOnScrollListener方法设置一下加载更多监听,在onLoadMore回调方法中,首先显示正在加载进度UI,然后模拟获取网络数据,完成之后隐藏加载进度UI,加载完两页数据之后显示到底了的提示。

3.封装

到这里,我们已经完成了RecyclerView的上拉加载更多功能,但是大部分的逻辑都写在了Adapter中,这样每写一个Adapter都要写一遍加载逻辑,这是很不优雅的,接下来我们对加载更多功能做一个封装,使其和Adapter完全解构,看下代码:

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

    private RecyclerView.Adapter adapter;

    // 普通布局
    private final int TYPE_ITEM = 1;
    // 脚布局
    private final int TYPE_FOOTER = 2;
    // 当前加载状态,默认为加载完成
    private int loadState = 2;
    // 正在加载
    public final int LOADING = 1;
    // 加载完成
    public final int LOADING_COMPLETE = 2;
    // 加载到底
    public final int LOADING_END = 3;

    public LoadMoreWrapper(RecyclerView.Adapter adapter) {
        this.adapter = adapter;
    }

    @Override
    public int getItemViewType(int position) {
        // 最后一个item设置为FooterView
        if (position + 1 == getItemCount()) {
            return TYPE_FOOTER;
        } else {
            return TYPE_ITEM;
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //进行判断显示类型,来创建返回不同的View
        if (viewType == TYPE_FOOTER) {
            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.layout_refresh_footer, parent, false);
            return new FootViewHolder(view);
        } else {
            return adapter.onCreateViewHolder(parent, viewType);
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof FootViewHolder) {
            FootViewHolder footViewHolder = (FootViewHolder) holder;
            switch (loadState) {
                case LOADING: // 正在加载
                    footViewHolder.pbLoading.setVisibility(View.VISIBLE);
                    footViewHolder.tvLoading.setVisibility(View.VISIBLE);
                    footViewHolder.llEnd.setVisibility(View.GONE);
                    break;

                case LOADING_COMPLETE: // 加载完成
                    footViewHolder.pbLoading.setVisibility(View.INVISIBLE);
                    footViewHolder.tvLoading.setVisibility(View.INVISIBLE);
                    footViewHolder.llEnd.setVisibility(View.GONE);
                    break;

                case LOADING_END: // 加载到底
                    footViewHolder.pbLoading.setVisibility(View.GONE);
                    footViewHolder.tvLoading.setVisibility(View.GONE);
                    footViewHolder.llEnd.setVisibility(View.VISIBLE);
                    break;

                default:
                    break;
            }
        } else {
            adapter.onBindViewHolder(holder, position);
        }
    }

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

    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
        RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
        if (manager instanceof GridLayoutManager) {
            final GridLayoutManager gridManager = ((GridLayoutManager) manager);
            gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                @Override
                public int getSpanSize(int position) {
                    // 如果当前是footer的位置,那么该item占据2个单元格,正常情况下占据1个单元格
                    return getItemViewType(position) == TYPE_FOOTER ? gridManager.getSpanCount() : 1;
                }
            });
        }
    }

    private class FootViewHolder extends RecyclerView.ViewHolder {

        ProgressBar pbLoading;
        TextView tvLoading;
        LinearLayout llEnd;

        FootViewHolder(View itemView) {
            super(itemView);
            pbLoading = (ProgressBar) itemView.findViewById(R.id.pb_loading);
            tvLoading = (TextView) itemView.findViewById(R.id.tv_loading);
            llEnd = (LinearLayout) itemView.findViewById(R.id.ll_end);
        }
    }

    /**
     * 设置上拉加载状态
     *
     * @param loadState 0.正在加载 1.加载完成 2.加载到底
     */
    public void setLoadState(int loadState) {
        this.loadState = loadState;
        notifyDataSetChanged();
    }
}

乍一看好像和上文中的LoadMoreAdapter没什么区别,都是继承了RecyclerView.Adapter并实现了其中的一些方法,但是仔细看会发现,构造方法中的参数变成了RecyclerView.Adapter,在LoadMoreWrapper中我们只处理加载更多功能相关的逻辑,其他逻辑交由Adapter本身处理,相当于扩展了Adapter的一些功能,嗯,这种方式还有一个学名,叫【装饰者模式】。

封装之后,Adapter中的代码变成了这样:

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

    private List<String> dataList;

    public LoadMoreWrapperAdapter(List<String> dataList) {
        this.dataList = dataList;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.adapter_recyclerview, parent, false);
        return new RecyclerViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        RecyclerViewHolder recyclerViewHolder = (RecyclerViewHolder) holder;
        recyclerViewHolder.tvItem.setText(dataList.get(position));
    }

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

    private class RecyclerViewHolder extends RecyclerView.ViewHolder {

        TextView tvItem;

        RecyclerViewHolder(View itemView) {
            super(itemView);
            tvItem = (TextView) itemView.findViewById(R.id.tv_item);
        }
    }
}

瞬间减少了一大半,使用起来也很简单,在原有Adapter的基础上包上一层就可以了:

LoadMoreWrapperAdapter loadMoreWrapperAdapter = new LoadMoreWrapperAdapter(dataList);
LoadMoreWrapper loadMoreWrapper = new LoadMoreWrapper(loadMoreWrapperAdapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(loadMoreWrapper);

4.写在最后

源码已经上传到GitHub上了,欢迎Fork,觉得还不错就Start一下吧!

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