View-RecyclerView支持添加头尾View的Adap

ListView中可以通过以下这两个方法设置头部和尾部的view，我们研究listView的源码来为rv添加同样的方法。

listView.addHeaderView();
listView.addFooterView();

添加头部

public void addHeaderView(View v, Object data, boolean isSelectable) {
      if (v.getParent() != null && v.getParent() != this) {
          if (Log.isLoggable(TAG, Log.WARN)) {
              Log.w(TAG, "The specified child already has a parent. "
                         + "You must call removeView() on the child's parent first.");
          }
      }
      final FixedViewInfo info = new FixedViewInfo();
      info.view = v;
      info.data = data;
      info.isSelectable = isSelectable;
      //1.添加到头部集合
      mHeaderViewInfos.add(info);
      mAreAllItemsSelectable &= isSelectable;

      // Wrap the adapter if it wasn't already wrapped.
      //2.适配器不为null
      if (mAdapter != null) {
          if (!(mAdapter instanceof HeaderViewListAdapter)) {
              //3.在原来的Adapter上进行一层包装
              wrapHeaderListAdapterInternal();
          }

          // In the case of re-adding a header view, or adding one later on,
          // we need to notify the observer.
          if (mDataSetObserver != null) {
              mDataSetObserver.onChanged();
          }
      }
  }

protected HeaderViewListAdapter wrapHeaderListAdapterInternal(
          ArrayList<ListView.FixedViewInfo> headerViewInfos,
          ArrayList<ListView.FixedViewInfo> footerViewInfos,
          ListAdapter adapter) {
      return new HeaderViewListAdapter(headerViewInfos, footerViewInfos, adapter);
  }

  /** @hide */
  protected void wrapHeaderListAdapterInternal() {
      mAdapter = wrapHeaderListAdapterInternal(mHeaderViewInfos, mFooterViewInfos, mAdapter);
  }

public void addFooterView(View v, Object data, boolean isSelectable) {
      if (v.getParent() != null && v.getParent() != this) {
          if (Log.isLoggable(TAG, Log.WARN)) {
              Log.w(TAG, "The specified child already has a parent. "
                         + "You must call removeView() on the child's parent first.");
          }
      }

      final FixedViewInfo info = new FixedViewInfo();
      info.view = v;
      info.data = data;
      info.isSelectable = isSelectable;
    //1. 添加到尾部集合
      mFooterViewInfos.add(info);
      mAreAllItemsSelectable &= isSelectable;

      // Wrap the adapter if it wasn't already wrapped.
      //2.适配器不为null
      if (mAdapter != null) {
          if (!(mAdapter instanceof HeaderViewListAdapter)) {
             //3.在原来的Adapter上进行一层包装
              wrapHeaderListAdapterInternal();
          }

          // In the case of re-adding a footer view, or adding one later on,
          // we need to notify the observer.
          if (mDataSetObserver != null) {
              mDataSetObserver.onChanged();
          }
      }
  }

封装的适配器

public class HeaderViewListAdapter implements WrapperListAdapter, Filterable {

  @UnsupportedAppUsage
  private final ListAdapter mAdapter;

  // These two ArrayList are assumed to NOT be null.
  // They are indeed created when declared in ListView and then shared.
  @UnsupportedAppUsage
  ArrayList<ListView.FixedViewInfo> mHeaderViewInfos;
  @UnsupportedAppUsage
  ArrayList<ListView.FixedViewInfo> mFooterViewInfos;

  // Used as a placeholder in case the provided info views are indeed null.
  // Currently only used by some CTS tests, which may be removed.
  static final ArrayList<ListView.FixedViewInfo> EMPTY_INFO_LIST =
      new ArrayList<ListView.FixedViewInfo>();

  boolean mAreAllFixedViewsSelectable;

  private final boolean mIsFilterable;

  public HeaderViewListAdapter(ArrayList<ListView.FixedViewInfo> headerViewInfos,
                               ArrayList<ListView.FixedViewInfo> footerViewInfos,
                               ListAdapter adapter) {
      mAdapter = adapter;
      mIsFilterable = adapter instanceof Filterable;

      if (headerViewInfos == null) {
          mHeaderViewInfos = EMPTY_INFO_LIST;
      } else {
          mHeaderViewInfos = headerViewInfos;
      }

      if (footerViewInfos == null) {
          mFooterViewInfos = EMPTY_INFO_LIST;
      } else {
          mFooterViewInfos = footerViewInfos;
      }

      mAreAllFixedViewsSelectable =
              areAllListInfosSelectable(mHeaderViewInfos)
              && areAllListInfosSelectable(mFooterViewInfos);
  }

  public int getHeadersCount() {
      return mHeaderViewInfos.size();
  }

  public int getFootersCount() {
      return mFooterViewInfos.size();
  }

  public boolean isEmpty() {
      return mAdapter == null || mAdapter.isEmpty();
  }

  private boolean areAllListInfosSelectable(ArrayList<ListView.FixedViewInfo> infos) {
      if (infos != null) {
          for (ListView.FixedViewInfo info : infos) {
              if (!info.isSelectable) {
                  return false;
              }
          }
      }
      return true;
  }

  public boolean removeHeader(View v) {
      for (int i = 0; i < mHeaderViewInfos.size(); i++) {
          ListView.FixedViewInfo info = mHeaderViewInfos.get(i);
          if (info.view == v) {
              mHeaderViewInfos.remove(i);

              mAreAllFixedViewsSelectable =
                      areAllListInfosSelectable(mHeaderViewInfos)
                      && areAllListInfosSelectable(mFooterViewInfos);

              return true;
          }
      }

      return false;
  }

  public boolean removeFooter(View v) {
      for (int i = 0; i < mFooterViewInfos.size(); i++) {
          ListView.FixedViewInfo info = mFooterViewInfos.get(i);
          if (info.view == v) {
              mFooterViewInfos.remove(i);

              mAreAllFixedViewsSelectable =
                      areAllListInfosSelectable(mHeaderViewInfos)
                      && areAllListInfosSelectable(mFooterViewInfos);

              return true;
          }
      }

      return false;
  }

  public int getCount() {
      if (mAdapter != null) {
          return getFootersCount() + getHeadersCount() + mAdapter.getCount();
      } else {
          return getFootersCount() + getHeadersCount();
      }
  }

  public boolean areAllItemsEnabled() {
      if (mAdapter != null) {
          return mAreAllFixedViewsSelectable && mAdapter.areAllItemsEnabled();
      } else {
          return true;
      }
  }

  public boolean isEnabled(int position) {
      // Header (negative positions will throw an IndexOutOfBoundsException)
      int numHeaders = getHeadersCount();
      if (position < numHeaders) {
          return mHeaderViewInfos.get(position).isSelectable;
      }

      // Adapter
      final int adjPosition = position - numHeaders;
      int adapterCount = 0;
      if (mAdapter != null) {
          adapterCount = mAdapter.getCount();
          if (adjPosition < adapterCount) {
              return mAdapter.isEnabled(adjPosition);
          }
      }

      // Footer (off-limits positions will throw an IndexOutOfBoundsException)
      return mFooterViewInfos.get(adjPosition - adapterCount).isSelectable;
  }

  public Object getItem(int position) {
      // Header (negative positions will throw an IndexOutOfBoundsException)
      int numHeaders = getHeadersCount();
      if (position < numHeaders) {
          return mHeaderViewInfos.get(position).data;
      }

      // Adapter
      final int adjPosition = position - numHeaders;
      int adapterCount = 0;
      if (mAdapter != null) {
          adapterCount = mAdapter.getCount();
          if (adjPosition < adapterCount) {
              return mAdapter.getItem(adjPosition);
          }
      }

      // Footer (off-limits positions will throw an IndexOutOfBoundsException)
      return mFooterViewInfos.get(adjPosition - adapterCount).data;
  }

  public long getItemId(int position) {
      int numHeaders = getHeadersCount();
      if (mAdapter != null && position >= numHeaders) {
          int adjPosition = position - numHeaders;
          int adapterCount = mAdapter.getCount();
          if (adjPosition < adapterCount) {
              return mAdapter.getItemId(adjPosition);
          }
      }
      return -1;
  }

  public boolean hasStableIds() {
      if (mAdapter != null) {
          return mAdapter.hasStableIds();
      }
      return false;
  }

  public View getView(int position, View convertView, ViewGroup parent) {
      // Header (negative positions will throw an IndexOutOfBoundsException)
      int numHeaders = getHeadersCount();
      if (position < numHeaders) {
          return mHeaderViewInfos.get(position).view;
      }

      // Adapter
      final int adjPosition = position - numHeaders;
      int adapterCount = 0;
      if (mAdapter != null) {
          adapterCount = mAdapter.getCount();
          if (adjPosition < adapterCount) {
              return mAdapter.getView(adjPosition, convertView, parent);
          }
      }

      // Footer (off-limits positions will throw an IndexOutOfBoundsException)
      return mFooterViewInfos.get(adjPosition - adapterCount).view;
  }

  public int getItemViewType(int position) {
      int numHeaders = getHeadersCount();
      if (mAdapter != null && position >= numHeaders) {
          int adjPosition = position - numHeaders;
          int adapterCount = mAdapter.getCount();
          if (adjPosition < adapterCount) {
              return mAdapter.getItemViewType(adjPosition);
          }
      }

      return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
  }

  public int getViewTypeCount() {
      if (mAdapter != null) {
          return mAdapter.getViewTypeCount();
      }
      return 1;
  }

  public void registerDataSetObserver(DataSetObserver observer) {
      if (mAdapter != null) {
          mAdapter.registerDataSetObserver(observer);
      }
  }

  public void unregisterDataSetObserver(DataSetObserver observer) {
      if (mAdapter != null) {
          mAdapter.unregisterDataSetObserver(observer);
      }
  }

  public Filter getFilter() {
      if (mIsFilterable) {
          return ((Filterable) mAdapter).getFilter();
      }
      return null;
  }
  
  public ListAdapter getWrappedAdapter() {
      return mAdapter;
  }
}

大致原理:在原来的mAdapter的基础上，分别向头部和尾部添加view集合，然后重新计算和返回位置和大小等。

2.实现可添加首尾部的基类Adapter

思路：在基类的adapter中增加HeaderAndFooterAdapter属性，如果用户想添加首尾view则设置为HeaderAndFooterAdapter，如果不添加则直接设置为Adapter。

public abstract class RecyclerViewAdapter<M, VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<VH> {

  protected List<M> mDataList = new ArrayList<>();
  private HeaderAndFooterAdapter mHeaderAndFooterAdapter;
  private Context mContext;

  public RecyclerViewAdapter(Context context) {
      this.mContext = context;
  }

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

  /**
   * @return 获取指定索引位置的数据模型
   */
  public M getItem(int position) {
      if (mDataList != null && position >= 0 && mDataList.size() > position) {
          return mDataList.get(position);
      } else {
          return null;
      }
  }

  /**
   * @return 获取数据集合
   */
  public List<M> getDataList() {
      return mDataList;
  }

  /**
   * @return 数据列表是否为空
   */
  public boolean isDataListEmpty() {
      return (mDataList == null || mDataList.size() <= 0);
  }

  /**
   * @param data 在指定位置添加新的数据
   */
  public void addData(M data, int position) {
      if (data != null && mDataList.size() >= position) {
          mDataList.add(position, data);
          notifyDataSetChangedWrapper();
      }
  }

  /**
   * @param data 在集合尾部添加新的数据
   */
  public void addMoreData(M data) {
      if (data != null) {
          mDataList.add(data);
          notifyDataSetChangedWrapper();
      }
  }

  /**
   * @param list 在集合尾部添加更多数据集合
   */
  public void addMoreData(List<M> list) {
      if (list != null && list.size() >= 0) {
          int positionStart = mDataList.size();
          mDataList.addAll(positionStart, list);
          notifyItemRangeInsertedWrapper(positionStart, list.size());
      }
  }

  /**
   * @param list 在集合头部部添加更多数据集合
   */
  public void addHeadData(List<M> list) {
      if (list != null && list.size() >= 0) {
          mDataList.addAll(0, list);
          notifyItemRangeInsertedWrapper(0, list.size());
      }
  }

  /**
   * @param data 设置全新的数据集合，如果传入空（null或空表），则清空数据列表
   *             （第一次从服务器加载数据，或者下拉刷新当前界面数据表）
   */
  public void setData(List<M> data) {
      mDataList.clear();
      if (data != null && data.size() >= 0) {
          mDataList.addAll(data);
      }
      notifyDataSetChangedWrapper();
  }

  /**
   * 清空数据列表
   */

  public void clear() {
      mDataList.clear();
      notifyDataSetChangedWrapper();
  }

  public Context getContext() {
      return mContext;
  }

  private void notifyItemRangeInsertedWrapper(int positionStart, int itemCount) {
      if (mHeaderAndFooterAdapter == null) {
          notifyItemRangeInserted(positionStart, itemCount);
      } else {
          mHeaderAndFooterAdapter.notifyItemRangeInserted(mHeaderAndFooterAdapter.getHeadersCount() + positionStart, itemCount);
      }
  }

  private void notifyItemRangeChangedWrapper(int positionStart, int itemCount) {
      if (mHeaderAndFooterAdapter == null) {
          notifyItemRangeChanged(positionStart, itemCount);
      } else {
          mHeaderAndFooterAdapter.notifyItemRangeChanged(mHeaderAndFooterAdapter.getHeadersCount() + positionStart, itemCount);
      }
  }

  //刷新数据区域，即不刷Header和Footer
  protected void notifyDataItemsChanged() {
      try {
          notifyItemRangeChangedWrapper(0, getItemCount());
      } catch (Exception e) {
          e.printStackTrace();
      }
  }

  public final void notifyDataSetChangedWrapper() {
      //如果没有头尾view的Adapter，则直接更新
      if (mHeaderAndFooterAdapter == null) {
          notifyDataSetChanged();
      } else {
          //否则，要通知头尾view的Adapter更新
          mHeaderAndFooterAdapter.notifyDataSetChanged();
      }
  }

  public final void notifyItemChangedWrapper(int position) {
      if (mHeaderAndFooterAdapter == null) {
          notifyItemChanged(position);
      } else {
          mHeaderAndFooterAdapter.notifyItemChanged(mHeaderAndFooterAdapter.getHeadersCount() + position);
      }
  }

  public void addHeaderView(View headerView) {
      getHeaderAndFooterAdapter().addHeaderView(headerView);
  }

  public void addFooterView(View footerView) {
      getHeaderAndFooterAdapter().addFooterView(footerView);
  }

  public int getHeadersCount() {
      return mHeaderAndFooterAdapter == null ? 0 : mHeaderAndFooterAdapter.getHeadersCount();
  }

  public int getFootersCount() {
      return mHeaderAndFooterAdapter == null ? 0 : mHeaderAndFooterAdapter.getFootersCount();
  }

  public HeaderAndFooterAdapter getHeaderAndFooterAdapter() {
      if (mHeaderAndFooterAdapter == null) {
          synchronized (RecyclerViewAdapter.this) {
              if (mHeaderAndFooterAdapter == null) {
                  mHeaderAndFooterAdapter = new HeaderAndFooterAdapter(this);
              }
          }
      }
      return mHeaderAndFooterAdapter;
  }
}

可添加首尾view的Adapter

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

  private static final int BASE_ITEM_TYPE_HEADER = 2048;
  private static final int BASE_ITEM_TYPE_FOOTER = 4096;

  private SparseArrayCompat<View> mHeaderViews = new SparseArrayCompat<>();
  private SparseArrayCompat<View> mFooterViews = new SparseArrayCompat<>();
  private RecyclerView.Adapter mAdapter;

  public HeaderAndFooterAdapter(@NonNull RecyclerView.Adapter adapter) {
      mAdapter = adapter;
  }

  @NonNull
  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
      if (mHeaderViews.get(viewType) != null) {
          return new RecyclerView.ViewHolder(mHeaderViews.get(viewType)) {
          };
      } else if (mFooterViews.get(viewType) != null) {
          return new RecyclerView.ViewHolder(mFooterViews.get(viewType)) {
          };
      } else {
          return mAdapter.onCreateViewHolder(parent, viewType);
      }

  }

  @Override
  public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
      //如果是header 或 footer就不绑定数据
      if (isHeaderViewOrFooterView(position)) {
          return;
      }

      mAdapter.onBindViewHolder(holder, getRealItemPosition(position));
  }

  @Override
  public int getItemViewType(int position) {
      if (isHeaderView(position)) {
          return mHeaderViews.keyAt(position);
      } else if (isFooterView(position)) {
          return mFooterViews.keyAt(position - getHeadersCount() - getRealItemCount());
      } else {
          return mAdapter.getItemViewType(getRealItemPosition(position));
      }
  }

  @Override
  public int getItemCount() {
      return getHeadersCount() + getFootersCount() + getRealItemCount();
  }

  @Override
  public void onAttachedToRecyclerView(@NonNull RecyclerView recyclerView) {
      mAdapter.onAttachedToRecyclerView(recyclerView);

      RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();

      if (layoutManager instanceof GridLayoutManager) {
          final GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
          final GridLayoutManager.SpanSizeLookup spanSizeLookup = gridLayoutManager.getSpanSizeLookup();

          gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
              @Override
              public int getSpanSize(int position) {
                  if (isHeaderViewOrFooterView(position)) {
                      return gridLayoutManager.getSpanCount();
                  } else {
                      if (spanSizeLookup != null) {
                          return spanSizeLookup.getSpanSize(position);
                      }
                  }
                  return 1;
              }
          });
      }
  }

  @Override
  public void onViewAttachedToWindow(@NonNull RecyclerView.ViewHolder holder) {
      mAdapter.onViewAttachedToWindow(holder);
      int position = holder.getLayoutPosition();
      if (isHeaderViewOrFooterView(position)) {
          ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
          if (lp != null && lp instanceof StaggeredGridLayoutManager.LayoutParams) {
              StaggeredGridLayoutManager.LayoutParams p = (StaggeredGridLayoutManager.LayoutParams) lp;
              p.setFullSpan(true);
          }
      }
  }

  private boolean isHeaderViewOrFooterView(int position) {
      return isHeaderView(position) || isFooterView(position);
  }

  private int getRealItemPosition(int position) {
      return position - getHeadersCount();
  }

  public boolean isHeaderView(int position) {
      return position < getHeadersCount();
  }

  public boolean isFooterView(int position) {
      return position >= getHeadersCount() + getRealItemCount();
  }

  public void addHeaderView(View view) {
      mHeaderViews.put(mHeaderViews.size() + BASE_ITEM_TYPE_HEADER, view);
  }

  public void addFooterView(View view) {
      mFooterViews.put(mFooterViews.size() + BASE_ITEM_TYPE_FOOTER, view);
  }

  public int getRealItemCount() {
      return mAdapter.getItemCount();
  }

  public int getHeadersCount() {
      return mHeaderViews.size();
  }

  public int getFootersCount() {
      return mFooterViews.size();
  }
}

使用

public class MainActivity extends AppCompatActivity {

  private RecyclerView mRecyclerView;
  private RvAdapter mAdapter;
  private List<String> mData = new ArrayList<>();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      for (int i = 0; i < 23; i++) {
          mData.add("" + i);
      }
      mRecyclerView = findViewById(R.id.rv);
      mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
      mAdapter = new RvAdapter(this);
      View header = LayoutInflater.from(this).inflate(R.layout.header_layout,mRecyclerView,false);
      View footer = LayoutInflater.from(this).inflate(R.layout.footer_layout,mRecyclerView,false);
      mAdapter.setData(mData);
      mAdapter.addHeaderView(header);
     // mAdapter.addHeaderView(footer);
      mAdapter.addFooterView(footer);

      //如果添加了首尾view，则设置这个adapter
      mRecyclerView.setAdapter(mAdapter.getHeaderAndFooterAdapter());

      // 没有添加首尾view，则直接adapter
      // mRecyclerView.setAdapter(mAdapter);

  }
}

效果

image.png image.png

代码地址