一个可支持添加首尾view的基类Adapter
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。
**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;
}
}
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);
}
}
