RecyclerView下拉刷新上拉加载

一 、前言

最近实在太忙，一个多礼拜没有更新文章了，于是今晚加班加点把demo写出来，现在都12点了才开始写文章。

1.我们的目标

把RecyclerView下拉刷新上拉加载更多加入到我们的开发者头条APP中。

2.效果图

3.实现步骤

• 找一个带上拉刷新下载加载更多的RecyclerView开源库，我们要站在巨人的肩膀上
• 下载下来自己先运行下demo，然后看看是不是我们需要的功能，觉得不错就把module依赖进来，整合主项目。
• 整合进来了之后，我们肯定需要进行修改，例如我这边就有滑动冲突，有多个headView等问题。

二 、具体实现

1.寻找RecyclerView上拉刷新下载加载开源库

我们找开源项目肯定首选github，去搜索一下一大堆，如果效果图是你想要的功能的话，然后找排名靠前，收藏比较多的项目吧，我找的项目是CommonPullToRefresh,支持ListView，RecyclerView，GridView，SwipeRefreshLayout等常用控件。我跑了一下Demo，没啥bug，挺好用的。

2.加入项目中

1).module导入进来，然后主项目依赖一下，这里有不会的看我另外一篇文章Android Studio 入门，里面有讲到Android Studio添加项目依赖。

2).代码实现,我们这边就是修改SelectedFragment

首先我们看布局文件的变化,在RecyclerView外面包裹了自定义的一个类PtrClassicFrameLayout,内部实现了下拉刷新，上拉加载更多。还可以设置自定义属性，都是啥意思我就不解释了，有兴趣的点击github上那个链接，讲解的很详细。

<?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="match_parent"
  android:orientation="vertical">
  <com.chanven.lib.cptr.PtrClassicFrameLayout xmlns:cube_ptr="http://schemas.android.com/apk/res-auto"
    android:id="@+id/test_recycler_view_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#f0f0f0"
    cube_ptr:ptr_duration_to_close="200"
    cube_ptr:ptr_duration_to_close_header="700"
    cube_ptr:ptr_keep_header_when_refresh="true"
    cube_ptr:ptr_pull_to_fresh="false"
cube_ptr:ptr_ratio_of_header_height_to_refresh="1.2"
    cube_ptr:ptr_resistance="1.8">
    <android.support.v7.widget.RecyclerView
      android:id="@+id/test_recycler_view"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
android:background="@android:color/white"/>
  </com.chanven.lib.cptr.PtrClassicFrameLayout>
</LinearLayout>

再来看onCreateView方法，这个代码就不解释了。

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState){
    View rootView = LayoutInflater.from(getActivity()).inflate(R.layout.fragment_selected, null);
    ptrClassicFrameLayout = (PtrClassicFrameLayout) rootView.findViewById(R.id.test_recycler_view_frame);
    mRecyclerView = (RecyclerView) rootView.findViewById(R.id.test_recycler_view);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    init();
    return rootView;
  }

在onCreateView里面调用了init()方法，我们来瞧瞧怎么实现的。这里解释一下为什么要对适配器进行包装，这样的目的在包装类里面处加入头部，底部View，处理点击事件。大家拿到源码了之后自己也可以看看。

  private void init() {
    //初始化适配器
    selectedAdapter = new SelectedRecyclerAdapter(getActivity());
    //对适配器进行封装
    mAdapter = new RecyclerAdapterWithHF(selectedAdapter);
    //把滚动Banner加入头部
    mAdapter.addCarouse(initCarouselHead());
    mRecyclerView.setAdapter(mAdapter);
    ptrClassicFrameLayout.setPtrHandler(ptrDefaultHandler);//设置下拉监听
    ptrClassicFrameLayout.setOnLoadMoreListener(onLoadMoreListener);//设置上拉监听
    ptrClassicFrameLayout.setLoadMoreEnable(true);//设置可以加载更多
  }

mAdapter.addCarouse(initCarouselHead()); 初始化一个滚动Banner，然后加入适配器头部。这个我前面的教程应该已经讲过了。。

  //初始化
  private View initCarouselHead(){
    View headView = LayoutInflater.from(getActivity()).inflate(R.layout.fragment_selected_header,mRecyclerView,false);
    tvContent=(TextView) headView.findViewById(R.id.tv_content);
    tvContent.setText(carousePageStr[0]);
    viewPager = (ViewPager)headView.findViewById(R.id.viewpager);
    selectedPagerAdapter=new SelectedPagerAdapter(getActivity(),carousePagerSelectView);
    viewPager.setOffscreenPageLimit(2);
    viewPager.setCurrentItem(0);
    viewPager.addOnPageChangeListener(onPageChangeListener);
    viewPager.setAdapter(selectedPagerAdapter);
    ViewGroup group = (ViewGroup) headView.findViewById(R.id.viewGroup);// 初始化底部显示控件
    tips = new ImageView[3];
    for (int i = 0; i < tips.length; i++){
      ImageView imageView = new ImageView(getActivity());
      if (i == 0) {
        imageView.setBackgroundResource(R.mipmap.page_indicator_focused);
      } else {
        imageView.setBackgroundResource(R.mipmap.page_indicator_unfocused);
      }
      tips[i] = imageView;
      LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT));
      layoutParams.leftMargin = 10;// 设置点点点view的左边距
      layoutParams.rightMargin = 10;// 设置点点点view的右边距
      group.addView(imageView, layoutParams);
    }
    timer = new Timer(true);//初始化计时器
    timer.schedule(task, 0, CAROUSEL_TIME);//延时0ms后执行,3000ms执行一次
    return headView;
  }

SelectedRecyclerAdapter 必须继承RecyclerView.Adapter

这玩意跟ListView的适配器差不多，用过ListView适配器的应该一看就懂了。

首先会调用getItemCount，知道我要显示多少item。

知道了行数然后就是循环调用onCreateViewHolder跟onBindViewHolder了，onCreateViewHolder就是创建一个item的View,onBindViewHolder就会把上次创建的item的View传入进来，还有一个下标，这样我们就能给每一行赋值，这两个方法都是先后一起调用。item回收重用的机制应该跟ListView一样的。

public class SelectedRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
  private List<SelectedArticle> selectedArticles;
  private LayoutInflater inflater;
  public SelectedRecyclerAdapter(Context context) {
    super();
    inflater = LayoutInflater.from(context);

    selectedArticles = new ArrayList<SelectedArticle>();
    initData();
  }
  private void initData() {
    for (int i = 0; i < 10; i++) {
      SelectedArticle selectedArticle = new SelectedArticle(i, "Android开发666", i, i, "");
      selectedArticles.add(selectedArticle);
    }
  }
  public void loadMore(int page) {
    for (int i = 0; i < 5; i++) {
      SelectedArticle selectedArticle = new SelectedArticle(i, "第" + page + "页数据", i, i, "");
      selectedArticles.add(selectedArticle);
    }
  }
  public void getFirst() {
    selectedArticles.clear();
    initData();
  }
  @Override
  public int getItemCount() {
    return selectedArticles.size();
  }
  @Override
  public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
    SelectedRecyclerHolder holder = (SelectedRecyclerHolder) viewHolder;
    SelectedArticle selectedArticle = selectedArticles.get(position);
    holder.title.setText(selectedArticle.getTitle());
    holder.like.setText("" + selectedArticle.getLikeNumber());
    holder.comment.setText("" + selectedArticle.getCommentNumber());
  }
  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewHolder, int position) {
    View view = inflater.inflate(R.layout.fragment_selected_item, null);
    return new SelectedRecyclerHolder(view);
  }
  public class SelectedRecyclerHolder extends RecyclerView.ViewHolder {
    private TextView title;//标题
    private TextView like;//喜欢数量
    private TextView comment;评论数量
    public SelectedRecyclerHolder(View view) {
      super(view);
      title = (TextView) view.findViewById(R.id.tv_title);
      like = (TextView) view.findViewById(R.id.tv_like);
      comment = (TextView) view.findViewById(R.id.tv_comment);
    }
  }
}

3.解决整合进来的bug

滑动冲突

当我们上拉到顶部把标题栏挤出屏幕外的时候,进行下拉会触发RecyclerView的下拉事件，正确的情况应该是显示Toolbar.

1).RecyclerView下拉刷新的时候先判断Toolbar有没有显示。如果Toolbar没有显示就不处理。

2).AppBarLayout有一个addOnOffsetChangedListener方法,在AppBarLayout的布局偏移量发生改变时被调用。

在MainFragment里面进行监听

appBarLayout= (AppBarLayout) rootView.findViewById(R.id.appBarLayout);
appBarLayout.addOnOffsetChangedListener(onOffsetChangedListener);

然后在回调函数中，把值给SelectedFragment，

  private AppBarLayout.OnOffsetChangedListener onOffsetChangedListener=new AppBarLayout.OnOffsetChangedListener() {
    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int i){
      //i>=0 Toolbar全部显示
      selectedFragment.setPullRefresh(i>=0);
      System.out.println("i值:"+i);
    }
  };

3).在SelectedFragment中，继续把值传给PtrFrameLayout

  public void setPullRefresh(boolean pullRefresh) {
    ptrClassicFrameLayout.setPullRefresh(pullRefresh);
  }

4.在PtrFrameLayout里面用一个实例变量接收这个值

  private boolean pullRefresh=true;
  public void setPullRefresh(boolean pullRefresh) {
    this.pullRefresh = pullRefresh;
  }

4).找到PtrFrameLayout类的dispatchTouchEvent事件,这个方法是处理屏幕的触摸事件的。

  @Override
  public boolean dispatchTouchEvent(MotionEvent e) {
    if (!isEnabled() || mContent == null || mHeaderView == null) {
      System.out.println("都是空的...");
      return dispatchTouchEventSupper(e);
    }
    int action = e.getAction();
    switch (action) {
      case MotionEvent.ACTION_UP:
        System.out.println("弹起...");
      case MotionEvent.ACTION_CANCEL:
         System.out.println("取消...");
//        if(pullRefresh){
          mPtrIndicator.onRelease();
          if (mPtrIndicator.hasLeftStartPosition()) {
            if (DEBUG) {
              PtrCLog.d(LOG_TAG, "call onRelease when user release");
            }
            System.out.println("call onRelease when user release");
            onRelease(false);
            if (mPtrIndicator.hasMovedAfterPressedDown()) {
              sendCancelEvent();
              return true;
            }
          }
          return dispatchTouchEventSupper(e);
//        }
      case MotionEvent.ACTION_DOWN:
        System.out.println("按下...");
        mHasSendCancelEvent = false;
        mPtrIndicator.onPressDown(e.getX(), e.getY());
        mScrollChecker.abortIfWorking();
        mPreventForHorizontal = false;
        // The cancel event will be sent once the position is moved.
        // So let the event pass to children.
        // fix #93, #102
        return dispatchTouchEventSupper(e);
      case MotionEvent.ACTION_MOVE:
        System.out.println("移动...");
        if(pullRefresh){//Toolbar显示
          mLastMoveEvent = e;
          mPtrIndicator.onMove(e.getX(), e.getY());
          float offsetX = mPtrIndicator.getOffsetX();
          float offsetY = mPtrIndicator.getOffsetY();
          if (mDisableWhenHorizontalMove && !mPreventForHorizontal && (Math.abs(offsetX) > mPagingTouchSlop && Math.abs(offsetX) > Math.abs(offsetY))) {
            if (mPtrIndicator.isInStartPosition()) {
              mPreventForHorizontal = true;
            }
          }
          if (mPreventForHorizontal) {
            return dispatchTouchEventSupper(e);
          }
          boolean moveDown = offsetY > 0;
          boolean moveUp = !moveDown;
          boolean canMoveUp = mPtrIndicator.hasLeftStartPosition();
          if (DEBUG) {
            boolean canMoveDown = mPtrHandler != null && mPtrHandler.checkCanDoRefresh(this, mContent, mHeaderView);
            PtrCLog.v(LOG_TAG, "ACTION_MOVE: offsetY:%s, currentPos: %s, moveUp: %s, canMoveUp: %s, moveDown: %s: canMoveDown: %s", offsetY, mPtrIndicator.getCurrentPosY(), moveUp, canMoveUp, moveDown, canMoveDown);
          }
          // disable move when header not reach top
          if (moveDown && mPtrHandler != null && !mPtrHandler.checkCanDoRefresh(this, mContent, mHeaderView)) {
            return dispatchTouchEventSupper(e);
          }
          if ((moveUp && canMoveUp) || moveDown) {
//            System.out.println("是否下拉刷新:"+pullRefresh+"偏移量是多少:"+offsetY);
            movePos(offsetY);
            return true;
          }
        }
    }
    return dispatchTouchEventSupper(e);
  }

我就改了一行代码，在action==MotionEvent.ACTION_MOVE的时候，先判断我们传入的pullRefresh是否为true。。。

顶部加入轮播

RecyclerView头部底部加入View，前面我们介绍过了，都是适配器的封装类RecyclerAdapterWithHF来控制。从效果图中，我们可以看出，轮播的View是加入头部的，找到RecyclerAdapterWithHF类，看看源码依葫芦画瓢就可以了。

1).得有一个保存View的集合，其实用一个变量也行，因为我们只有一个轮播View.

  private List<View> mCarouse = new ArrayList<View>();//保存轮播View
  //可以添加轮播View
  public void addCarouse(View view){
    mCarouse.add(view);
  }

2).定义一个常量，用于类型判断

public static final int TYPE_CAROUSE = 7900;

3).在getItemViewType里面加入轮播的类型

  @Override
  public final int getItemViewType(int position) {
    // check what type our position is, based on the assumption that the
    // order is headers > items > footers
    if (isHeader(position)) {
      return TYPE_HEADER;
    } else if (mCarouse.size()>0&&mHeaders.size()==position){ //判断集合个数&&position==0 这个时候mHeaders里面是没有值的
      return TYPE_CAROUSE;
    }else if (isFooter(position)) {
      return TYPE_FOOTER;
    }
    int type = getItemViewTypeHF(getRealPosition(position));
    if (type == TYPE_HEADER || type == TYPE_FOOTER|| type == TYPE_CAROUSE) {
      throw new IllegalArgumentException("Item type cannot equal " + TYPE_HEADER + " or " + TYPE_FOOTER);
    }
    return type;
  }

4).onCreateViewHolder里面也要修改一下，就是在if里面多加了个&&.无论是头部，底部，轮播的View，都是添加到FrameLayout里面的。

  @Override
  public final RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int type) {
    // if our position is one of our items (this comes from
    // getItemViewType(int position) below)
    if (type != TYPE_HEADER && type != TYPE_FOOTER && type != TYPE_CAROUSE) {
      ViewHolder vh = onCreateViewHolderHF(viewGroup, type);
      return vh;
      // else we have a header/footer
    } else {
      // create a new framelayout, or inflate from a resource
      FrameLayout frameLayout = new FrameLayout(viewGroup.getContext());
      // make sure it fills the space
      frameLayout.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
      return new HeaderFooterViewHolder(frameLayout);
    }
  }

5).onBindViewHolder这里为item绑定数据，其实就是第四步返回的ItemView绑定数据.

  @Override
  public final void onBindViewHolder(final RecyclerView.ViewHolder vh, int position){
    // check what type of view our position is
    if (isHeader(position)) {
      View v = mHeaders.get(position);
      // add our view to a header view and display it
      prepareHeaderFooter((HeaderFooterViewHolder) vh, v);
    }else if(mCarouse.size()>0&&position==mHeaders.size()){//这个时候mHeaders.size()值为0
//      System.out.println("有多少个头View:"+mHeaders.size()+"值等于多少:"+(mHeaders.size()-1));
      View v = mCarouse.get(mHeaders.size());//取出轮播的View
      prepareHeaderFooter((HeaderFooterViewHolder) vh, v);
    } else if (isFooter(position)) {
      View v = mFooters.get(position - getItemCountHF() - mHeaders.size());
      // add our view to a footer view and display it
      prepareHeaderFooter((HeaderFooterViewHolder) vh, v);
    } else {
      vh.itemView.setOnClickListener(new MyOnClickListener(vh));
      vh.itemView.setOnLongClickListener(new MyOnLongClickListener(vh));
      // it's one of our items, display as required
      onBindViewHolderHF(vh, getRealPosition(position));
    }
  }

6).我们从第五步看到头部底部轮播View最后都会调用prepareHeaderFooter方法。看到这方法的源码，其实就是把类型对应的View，添加到Item中.

  private void prepareHeaderFooter(HeaderFooterViewHolder vh, View view) {
    // if it's a staggered grid, span the whole layout
    if (mManagerType == TYPE_MANAGER_STAGGERED_GRID) {
      StaggeredGridLayoutManager.LayoutParams layoutParams = new StaggeredGridLayoutManager.LayoutParams   (ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT);
      layoutParams.setFullSpan(true);
      vh.itemView.setLayoutParams(layoutParams);
    }
    // if the view already belongs to another layout, remove it
    if (view.getParent() != null) {
      ((ViewGroup) view.getParent()).removeView(view);
    }
    // empty out our FrameLayout and replace with our header/footer
    vh.base.removeAllViews();
    vh.base.addView(view);
  }

以上就是本文的全部内容，希望本文的内容对大家的学习或者工作能带来一定的帮助，同时也希望多多支持我们！