RecyclerView的下拉刷新与上拉加载更多

下拉刷新和上拉加载更多，从设计层面上来说，就不是同一个层面上的，从Google官方推出的下拉刷新控件SwipeRefreshLayout就可以看出。
一般来说，下拉刷新是以包裹整个列表控件的容器来实现的，而上拉加载更多是以列表控件的一部分扩展（footerView）来实现的。

下拉刷新

1. Google官方的SwipeRefreshLayout
   xml中控件初始化：

   <android.support.v4.widget.SwipeRefreshLayout
       android:layout_width="match_parent"
       android:layout_height="match_parent">
   
       <android.support.v7.widget.RecyclerView
           android:id="@+id/recyclerView"
           android:layout_width="match_parent"
           android:layout_height="match_parent"/>
   
   </android.support.v4.widget.SwipeRefreshLayout>

java类中实现

// 设置下拉出现小圆圈是否是缩放出现，出现的位置，最大的下拉位置
mySwipeRefreshLayout.setProgressViewOffset(true, 50, 200);

// 设置下拉圆圈的大小，两个值 LARGE， DEFAULT
mySwipeRefreshLayout.setSize(SwipeRefreshLayout.LARGE);

// 设置下拉圆圈上的颜色，蓝色、绿色、橙色、红色
mySwipeRefreshLayout.setColorSchemeResources(
        android.R.color.holo_blue_bright,
        android.R.color.holo_green_light,
        android.R.color.holo_orange_light,
        android.R.color.holo_red_light);

// 通过 setEnabled(false) 禁用下拉刷新
mySwipeRefreshLayout.setEnabled(false);

// 设定下拉圆圈的背景
mSwipeLayout.setProgressBackgroundColor(R.color.red);

/*
 * 设置手势下拉刷新的监听
 */
mySwipeRefreshLayout.setOnRefreshListener(
        new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                // 刷新动画开始后回调到此方法
            }
        }
);

1. 使用第三方下拉刷新控件，可以更好地支持自定义下拉样式。
   这里推荐一个比较好的第三方控件：android-Ultra-Pull-To-Refresh

   compile 'in.srain.cube:ultra-ptr:1.0.10'

xml中控件初始化：

<in.srain.cube.views.ptr.PtrFrameLayout
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/refreshView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:ptr_duration_to_close="200"
    app:ptr_duration_to_close_header="1000"
    app:ptr_keep_header_when_refresh="true"
    app:ptr_pull_to_fresh="false"
    app:ptr_ratio_of_header_height_to_refresh="1.2"
    app:ptr_resistance="1.7">

    <com.zdf.zhihu.view.widget.LoadMoreRecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    </com.zdf.zhihu.view.widget.LoadMoreRecyclerView>

</in.srain.cube.views.ptr.PtrFrameLayout>

java类中实现：

private void initRefreshView() {
    // 这里可以完全自定义各种样式，只要实现PtrUIHandler，
    // 具体请参考官方文档也源码
    MaterialHeader header = new MaterialHeader(getContext());
    refreshView.setHeaderView(header);
    refreshView.addPtrUIHandler(header);
    refreshView.setPtrHandler(new PtrDefaultHandler() {
        @Override
        public void onRefreshBegin(PtrFrameLayout ptrFrameLayout) {
            page = 0;
            requestTopMovies();
        }
    });
}

@Override
public void autoRefresh() {
    handler.postDelayed(new Runnable() {
        @Override
        public void run() {
            refreshView.autoRefresh();
        }
    }, 100);
}

@Override
public void refreshComplete() {
    handler.post(new Runnable() {
        @Override
        public void run() {
            refreshView.refreshComplete();
        }
    });
}

上拉加载更多

以列表控件的一部分扩展实现，这里以RecyclerView为例，新建一个类LoadMoreRecyclerView，继承至RecyclerView，主要的功能就是实现加载更多逻辑和显示控件：

/**
 * 集成了上拉加载更多的RecyclerView
 *
 * Created by XiaoFeng on 2017/2/3.
 */
public class LoadMoreRecyclerView extends RecyclerView {

    private final int STATE_NONE = 0x00;
    private final int STATE_LOADING = 0x01;
    private final int STATE_FAILURE = 0x02;
    private final int STATE_COMPLETE = 0x03;

    // 滑到底部里最后一个个数的阀值
    private static final int VISIBLE_THRESHOLD = 1;

    private int state;
    private boolean loadMoreEnabled = true;
    private OnLoadMoreListener listener;
    private SuperAdapter superAdapter;
    private LoadMoreView loadMoreView;
    private LinearLayoutManager layoutManager;

    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);
    }

    public void initLoadMore(@NonNull OnLoadMoreListener listener) {
        this.listener = listener;

        if (getAdapter() instanceof SuperAdapter) {
            superAdapter = (SuperAdapter) getAdapter();
        }

        loadMoreView = new LoadMoreView(getContext());
        layoutManager = (LinearLayoutManager) getLayoutManager();

        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);

                if (canLoadMore() && dy >= 0) {
                    int totalItemCount = layoutManager.getItemCount();
                    int lastVisibleItem = layoutManager.findLastVisibleItemPosition();
                    if (lastVisibleItem + VISIBLE_THRESHOLD >= totalItemCount) {
                        onLoadMore(recyclerView);
                    }
                }
            }
        });
    }

    public void setLoadMoreEnabled(boolean enabled) {
        this.loadMoreEnabled = enabled;
    }

    private boolean canLoadMore() {
        return state != STATE_LOADING && loadMoreEnabled;
    }

    private void onLoadMore(RecyclerView recyclerView) {
        state = STATE_LOADING;

        if (loadMoreView != null) {
            loadMoreView.loading();
        }

        recyclerView.post(new Runnable() {
            @Override
            public void run() {
                if (state == STATE_LOADING) {
                    if (superAdapter != null && loadMoreView != null) {
                        superAdapter.addFooterView(loadMoreView);
                    }
                }
            }
        });

        if (listener != null) {
            listener.onLoadMore();
        }
    }

    public void loadMoreFailed() {
        state = STATE_FAILURE;

        if (loadMoreView != null) {
            loadMoreView.failure();
        }

        if (superAdapter != null) {
            superAdapter.removeFooterView();
        }
    }

    public void loadMoreComplete() {
        state = STATE_COMPLETE;

        if (loadMoreView != null) {
            loadMoreView.complete();
        }

        if (superAdapter != null) {
            superAdapter.removeFooterView();
        }
    }
}

上面出现的SuperAdapter是使用了一个第三方封装的万能Adapter，同时支持ListView和RecyclerView，个人感觉比鸿洋大神封装的万能Adapter要好一些，但是基本原理都是一样的。原理可以看他们各自的文章介绍，已经写的很详细了，这里就不多说了。

http://www.jianshu.com/p/d6a76fd3ea5b
http://blog.csdn.net/lmj623565791/article/details/38902805
http://blog.csdn.net/lmj623565791/article/details/51118836

关于分页加载

伴随着上拉加载更多功能的，往往是分页加载，关于分页加载的页数是在列表控件内部自动控制？还是在列表控件外部自己控制？我个人认为应该放在列表控件外部自己来控制页数，因为这个页数不光是在上拉加载更多时会使用到，在下拉刷新的时候也会使用到，并且对页数需要清零。
这里提供一种在列表控件外部控制页数的实现逻辑：

// 分页页数
private int page = 0;

// 初始化下拉刷新控件
private void initRefreshView() {
    MaterialHeader header = new MaterialHeader(getContext());
    refreshView.setHeaderView(header);
    refreshView.addPtrUIHandler(header);
    refreshView.setPtrHandler(new PtrDefaultHandler() {
        @Override
        public void onRefreshBegin(PtrFrameLayout ptrFrameLayout) {
            page = 0;
            requestTopMovies();
        }
    });
}

// 初始化RecyclerView，包含上拉加载更多
private void initRecyclerView() {
    recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
    adapter = new SubjectAdapter(getContext());
    recyclerView.setAdapter(adapter);
    recyclerView.initLoadMore(new OnLoadMoreListener() {
        @Override
        public void onLoadMore() {
            page++;
            requestTopMovies();
        }
    });
}

// 具有分页操作的网络请求
private void requestTopMovies() {
    Subscriber subscriber = new RxCallback<List<Movie>>() {
        @Override
        public void onSuccess(List<Movie> movieList) {
            if (adapter != null) {
                if (page == 0) {
                    adapter.clear();
                } else {
                    recyclerView.loadMoreComplete();
                }
                adapter.addAll(movieList);
            }
        }

        @Override
        public void onFinished() {
            refreshComplete();
        }
    };
    RxRetrofitClient.getInstance().requestTop250Movies(subscriber, page, 10);
}

参考:
https://github.com/hanks-zyh/SwipeRefreshLayout
http://www.jianshu.com/p/d6a76fd3ea5b
http://blog.csdn.net/lmj623565791/article/details/38902805
http://blog.csdn.net/lmj623565791/article/details/51118836