思路

• ListView中已经自带了添加头布局和添加底部布局的方法,但是在RecyclerView中，却没有默认实现,这导致在实现一些特殊布局中不是那么的方便.
• 在实现RecyclerView.Adapter的时候,有很多相同重复的代码,比如新增或者修改数据源、加载ViewHolder的布局文件
• 本次就是通过封装RecyclerView.Adapter，实现头部(header)、底部(footer)、空页面、ViewHolder.
• 本次封装用到了反射获取布局文件和ViewHolder，泛型指定数据源，使用dataBinding加载数据，使代码更加简洁
• 提供整个cell对外的点击事件

dataBinding的使用

• 需要在gradle文件里面添加

dataBinding {enabled = true
}
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• 不了解dataBinding的使用的,请百度搜索一下

BaseViewHolder的基本封装

• 使用泛型+dataBinding的形式,实现数据的绑定和更新

public class BaseViewHolder<T extends ViewDataBinding> extends RecyclerView.ViewHolder {public T t;/*** 是否用dataBanding* @param v* @param isBinding*/public BaseViewHolder(View v,boolean isBinding){super(v);if(isBinding){t = DataBindingUtil.bind(v);}}public BaseViewHolder(View v) {this(v,true);}
}
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布局文件和ViewHolder的注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Adapter {/*** 布局文件* @return*/@LayoutRes int layout();/*** ViewHolder的class* @return*/Class<? extends BaseViewHolder> holder();
}
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定义头部和底部的ViewHolder

/*** 头部和底部的ViewHolder*/
static class HeaderAndFooterViewHolder extends BaseViewHolder {public HeaderAndFooterViewHolder(View itemView) {super(itemView, false);}
}
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RecyclerAdapter的封装

• 通过反射+注解的方式获取cell的布局文件和ViewHolder的实体
• 定义头部、底部、空页面的不同类型,重写getItemViewType方法,更具下标,是否有头部和底部视图,是否需要加载空页面,来返回不同的类型.
• 重写onCreateViewHolder方法,根据不同的类型创建不同的ViewHolder.
• 重写onBindViewHolder方法,如果当前下标的类型是头部、底部、空页面，就不加载数据源，对外提供cell的点击事件
• GridLayoutManger和StaggeredGridLayoutManager跨列问题
• 代码如下

public abstract class RecyclerAdapter<M, VH extends BaseViewHolder>extends RecyclerView.Adapter<BaseViewHolder>{private List<M> mData;/*** 头部类型*/public static final int TYPE_HEADER = -1;/*** 底部类型*/public static final int TYPE_FOOTER = -2;/*** 无数据类型*/public static final int TYPE_EMPTY = -3;/*** 正常的item*/public static final int TYPE_NORMAL = 0;/*** 头部*/private View mHeaderView;/*** 底部*/private View mFooterView;/*** 是否展示空页面*/private boolean showEmpty;/*** 空页面layout*/private int emptyLayout = R.layout.view_load_empty;/*** 是否是第一次加载数据*/private boolean firstLoad = true;private RecyclerAdapter.OnItemClickListener mListener;/*** 分页处理器*/private IPageControl mPageControl;public RecyclerAdapter() {this(null);}public RecyclerAdapter(IPageControl pageControl) {mData = new ArrayList<>();mPageControl = pageControl;annotationAdapter();}private Adapter mAdapterAnnotation;/*** 获取@Adapter注解*/private void annotationAdapter() {Class cls = this.getClass();if (cls.isAnnotationPresent(Adapter.class)) {mAdapterAnnotation = this.getClass().getAnnotation(Adapter.class);}}/*** 设置空页面*/public void setEmptyLayout(@LayoutRes int emptyLayout) {this.emptyLayout = emptyLayout;}/*** 添加头部*/public void setHeaderView(View headerView) {mHeaderView = headerView;}/*** 获取头部*/public View getHeaderView() {return mHeaderView;}/*** 添加底部*/public void setFooterView(View footerView) {mFooterView = footerView;}/*** 获取底部*/public View getFooterView() {return mFooterView;}/*** 设置每行点击事件的监听*/public void setOnItemClickListener(RecyclerAdapter.OnItemClickListener listener) {mListener = listener;}public List<M> getData() {if (ListUtils.isEmpty(mData)) {throw new IllegalStateException("mData is empty(数据为空)");}return mData;}public M get(int position) {if (position < 0 || position > (mData.size() - 1)) {throw new IllegalStateException("position必须大于0,且不能大于mData的个数");}if (ListUtils.isEmpty(mData)) {return null;}return mData.get(position);}/*** 设置list为这个list*/public void set(List<M> data) {firstLoad = false;if (data != null) {mData = data;}notifyDataSetChanged();}/*** 清空数据*/public void clear() {mData.clear();notifyDataSetChanged();}/*** list中添加更多的数据*/public void add(List<M> data) {if (mData == null) {return;}mData.addAll(data);notifyDataSetChanged();}@Overridepublic int getItemViewType(int position) {if (position == 0 && showEmpty) {//当前数据空位,展示空页面return TYPE_EMPTY;}if (position == 0 && mHeaderView != null) {//当前view是头部信息return TYPE_HEADER;}if (position == getItemCount() - 1 && mFooterView != null) {//当前view是底部信息return TYPE_FOOTER;}return getCenterViewType(position);}/*** 标准的item的类型** @return 返回参数不能小于0*/@IntRange(from = 0)public int getCenterViewType(int position) {return TYPE_NORMAL;}@Overridepublic int getItemCount() {int size = mData == null ? 0 : mData.size();if (mHeaderView != null) {//有头部,item的个数+1size++;}if (mFooterView != null) {//有底部,item的个数+1size++;}if (size == 0) {showEmpty = true;size = 1;} else {showEmpty = false;}return size;}@Overridepublic BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {//加载头部信息if (TYPE_HEADER == viewType) {return new HeaderAndFooterViewHolder(mHeaderView);}//加载底部信息if (TYPE_FOOTER == viewType) {return new HeaderAndFooterViewHolder(mFooterView);}//加载空页面if (TYPE_EMPTY == viewType) {View v = inflate(emptyLayout, parent);return new HeaderAndFooterViewHolder(v);}//反射获取ViewHolderif (mAdapterAnnotation != null) {return reflectViewHolder(parent);}return createHolder(parent, viewType);}/*** 反射获得ViewHolder*/@SuppressWarnings("unchecked")private VH reflectViewHolder(ViewGroup parent) {View v = inflate(mAdapterAnnotation.layout(), parent);Class<VH> c = (Class<VH>) mAdapterAnnotation.holder();VH holder = null;try {Constructor<VH> con = c.getConstructor(View.class);holder = con.newInstance(v);} catch (NoSuchMethodException e) {System.err.println("检查ViewHolder类及构造函数是否是public");e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (InstantiationException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}return holder;}/*** 除头部和底部的ViewHolder的获取** @param viewType holder的类型*/protected VH createHolder(ViewGroup parent, int viewType) {return null;}/*** 获取需要viewHolder的view** @param layoutId 布局文件*/protected View inflate(int layoutId, ViewGroup group) {LayoutInflater inflater = LayoutInflater.from(group.getContext());return inflater.inflate(layoutId, group, false);}@SuppressWarnings("unchecked")@Overridepublic void onBindViewHolder(BaseViewHolder holder, final int position) {int index = position;if (mHeaderView != null) {//当前holder是头部就直接返回,不需要去设置viewholder的内容if (getItemViewType(position) == TYPE_HEADER) {return;} else {/** 有头部的情况,需要要减1,否则取item的数据会取到当前数据的下一条,* 取出最后一条数据的时候,会报下标溢出*/index--;}}if (mFooterView != null) {//当前holder是底部就直接返回,不需要去设置viewholder的内容if (getItemViewType(position) == TYPE_FOOTER) {return;}}//空页面状态,不需要设置holder的内容if (getItemViewType(position) == TYPE_EMPTY) {//第一次加载数据,不展示空页面if (firstLoad) {holder.itemView.setVisibility(View.INVISIBLE);} else {holder.itemView.setVisibility(View.VISIBLE);}return;}final int finalIndex = index;if (mData == null || mData.isEmpty() || index < 0 || index > mData.size() - 1) {return;}M m = mData.get(index);//设置item的点击回调事件holder.itemView.setOnClickListener(v -> {if (mListener != null) {mListener.itemClick(mRecyclerView.getId(), m, finalIndex);}});bindViewHolder((VH) holder, m, position);}/*** 绑定viewHolder的数据*/public abstract void bindViewHolder(VH holder, M m, int position);private RecyclerView mRecyclerView;/*** 处理RecyclerView.LayoutManager是GridLayoutManager类型,* 对头部和底部实体进行一个处理,使其占满一行* @param recyclerView*/@Overridepublic void onAttachedToRecyclerView(RecyclerView recyclerView) {super.onAttachedToRecyclerView(recyclerView);mRecyclerView = recyclerView;RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();if (manager instanceof GridLayoutManager) {final GridLayoutManager gridManager = ((GridLayoutManager) manager);gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {@Overridepublic int getSpanSize(int position) {return (getItemViewType(position) == TYPE_HEADER|| getItemViewType(position) == TYPE_FOOTER)? gridManager.getSpanCount() : 1;}});}}/*** 加入针对StaggeredGridLayoutManager跨列处理的代码* 一个item通过adapter开始显示会被回调* @param holder*/@Overridepublic void onViewAttachedToWindow(BaseViewHolder holder) {super.onViewAttachedToWindow(holder);ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();if (lp != null&& lp instanceof StaggeredGridLayoutManager.LayoutParams&& holder.getLayoutPosition() == 0) {StaggeredGridLayoutManager.LayoutParams p =(StaggeredGridLayoutManager.LayoutParams) lp;//占满一行p.setFullSpan(true);}}/*** 头部和底部的ViewHolder*/static class HeaderAndFooterViewHolder extends BaseViewHolder {public HeaderAndFooterViewHolder(View itemView) {super(itemView, false);}}/*** item点击事件*/public interface OnItemClickListener<M> {/*** @param id RecyclerView.getId()* @param m item下的实体* @param position item所在的位置*/void itemClick(@IdRes int id, M m, int position);}
}
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