RecyclerView进阶（一）通过装饰者模式添加头部底部

2017-08-24

效果图

通过装饰者模式添加头部底部

ListView提供了addHeadView和addFootView方法，使用起来非常方便，而ReyclerView则需要我们自己在adapter中判断，常规做法无外乎判断position==0，来添加头布局，不过这个做法只适合单个，而且不通用。
我们看下ListView.addHeadView是如何实现的

public void addHeaderView(View v, Object data, boolean isSelectable) {
        final FixedViewInfo info = new FixedViewInfo();
        info.view = v;
        info.data = data;
        info.isSelectable = isSelectable;
        mHeaderViewInfos.add(info);
        mAreAllItemsSelectable &= isSelectable;


        if (mAdapter != null) {
            if (!(mAdapter instanceof HeaderViewListAdapter)) {
                mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
            }


            if (mDataSetObserver != null) {
                mDataSetObserver.onChanged();
            }
        }
    }

这里 mAdapter = new HeaderViewListAdapter(mHeaderViewInfos,mFooterViewInfos, mAdapter)，new 了一个新的adapter，并把当前的adapter传进去了，这里其实采用的装饰者模式来做的，照着他的源码做一个试试。

1、创建WrapperHeadAndFootAdapter继承成RecylcerView.Adapter，同时，创建头部集合和底部集合，添加集合和移除集合方法。

这里采用SparseArray 取代HashMap 原因有两点：

SparseArray默认以int为key，少了拆箱装箱流程
在千量级，性能优于HashMap，并且更轻量,更省内存。

可以看看这篇 –> Android内存优化–SparseArray和ArrayMap

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

    //头布局集合
    public SparseArray<View> mHeads =new SparseArray<>();
    //底布局集合
    public SparseArray<View> mFoots =new SparseArray<>();
    //被装饰的Adapter
    public RecyclerView.Adapter mAdapter;
    //头部集合的key
    public static int HEAD_KEY=1000000;
    //底部集合的key
    public static int FOOT_KEY=3000000;

 public  WrapperHeadAndFootAdapter(RecyclerView.Adapter adapter){

        if(adapter==null){
            throw new IllegalArgumentException("adapter cannot null");
        }
         mAdapter=adapter;
    }

     @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

            return null;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {

    }


    @Override
    public int getItemCount() {
        return 0;
    }

       /**
     * 添加头布局
     */

    public void addHeadView(View view){
        if(mHeads.indexOfValue(view)==-1){
            mHeads.put(HEAD_KEY++,view);
        }
    }
    /**
     * 移除头布局
     */

    public void removeHeadView(View view){
       removeHeadView(view,-1);
    }

    /**
     * 移除头布局
     */

    public void removeHeadView(View view,int posistion){
        int index = mHeads.indexOfValue(view);
        if(index >=0){
            mHeads.removeAt(index);
        }
        notifyItemRemoved(posistion);
    }

    /**
     * 添加底布局
     */

    public void addFootView(View view){

        if(mFoots.indexOfValue(view)==-1){
            mFoots.put(FOOT_KEY++,view);
        }
    }

    /**
     * 删除底布局
     */

    public void removeFootView(View view){
        removeFootView(view,-1);
    }

    /**
     * 删除底布局
     */

    public void removeFootView(View view,int position){
        int index = mFoots.indexOfValue(view);
        if(index>0){
            mFoots.removeAt(index);
        }
        notifyItemRemoved(position);
    }

}

这里，可能有疑问为什么mHeads和mFoots的key取值分别为100000和300000，其实这里不一定非要是这个，你也可以是0或者负数，但是这里面有个问题，当在getItemViewType中，返回key的时候，假如是0，而我们的mAdapter的默认返回值就是0，那在onCreateViewHolder中就会产生冲突，尤其是多布局的情况下，viewType的值并不确定，所以保险起见，弄了一个这个值，这个值随意，只要保证不冲突即可。

   @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //头布局--viewType是mHeads的key
        if (mHeads.indexOfKey(viewType)>=0){
            return new RecyclerView.ViewHolder(mHeads.get(viewType)) {
            };
        }

        if(mFoots.indexOfKey(viewType)>=0){
            return new RecyclerView.ViewHolder(mFoots.get(viewType)) {
            };
        }
            return mAdapter.onCreateViewHolder(parent,viewType);

    }


    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        int normlPosition= position - mHeads.size();
        int itemCount = mAdapter.getItemCount();

        if(isHeadView(position)){
            //如果是头部，不绑定
                 if(onHeadClickListener!=null){
                 //设置头部的点击事件
                final View headView = mHeads.get(mHeads.keyAt(position));
                if(headView!=null){
                    headView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            onHeadClickListener.onClick(headView,getHeadPosition(headView));
                        }
                    });
                }
            }

            return;
        }

        if(isFootView(position)){
            //如果是底部，不绑定
            if(onFootClickListener!=null){
            //设置底部点击事件
                final View footView = mFoots.get(mFoots.keyAt(normlPosition-itemCount));
                if(footView!=null){
                    footView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            onFootClickListener.onClick(footView,getHeadPosition(footView));
                        }
                    });
                }
            return;
        }

        //正常布局

        if(normlPosition<itemCount){
            mAdapter.onBindViewHolder(holder,normlPosition);
        }

    }


    @Override
    public int getItemCount() {
        return mHeads.size()+mAdapter.getItemCount()+mFoots.size();
    }

    @Override
    public int getItemViewType(int position) {
        //头布局
        if(isHeadView(position)){
            return mHeads.keyAt(position);
        }
        //正常列表
        int normlPosition=position-mHeads.size();
        int itemCount = mAdapter.getItemCount();
        if(normlPosition<itemCount){

            return mAdapter.getItemViewType(normlPosition);
        }
        //底布局
        int footPosition=normlPosition-itemCount;
        return mFoots.keyAt(footPosition);
    }


    private boolean isFootView(int position){

        return position>=mHeads.size()+mAdapter.getItemCount();
    }

    private boolean isHeadView(int position){
        int size = mHeads.size();
        return position<size;
    }


     /**
     * 设置头部的点击事件
     * @param onHeadClickListener
     */
    public void setOnHeadClickListener(OnHeadClickListener onHeadClickListener){

        this.onHeadClickListener = onHeadClickListener;
    }

    /**
     * 设置底部的点击事件
     */

    public void setOnFootClickListener(OnFootClickListener onFootClickListener){

        this.onFootClickListener = onFootClickListener;
    }

    /**
     * 解决GridLayoutManager添加头部和底部不占用一行的问题
     */
    public void adjustSpanSize(RecyclerView recycler) {
        if (recycler.getLayoutManager() instanceof GridLayoutManager) {
            final GridLayoutManager layoutManager = (GridLayoutManager) recycler.getLayoutManager();
            layoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                @Override
                public int getSpanSize(int position) {
                    boolean isHeaderOrFooter = isHeaderPosition(position) || isFooterPosition(position);
                    return isHeaderOrFooter ? layoutManager.getSpanCount() : 1;
                }
            });
        }
    }

     /**
     * 获取头部的位置
     * @param view
     * @return
     */
    public int getHeadPosition(View view) {
        return  mHeads.indexOfValue(view);
    }

    /**
     * 获取底部的位置
     */

    public int getFootPosition(View view){
        int position=mFoots.indexOfValue(view)+mHeads.size()+mAdapter.getItemCount();
        return position;
    }

上面代码其实没什么好注意的，唯一注意的是在onBindViewHolder绑定数据的时候，如果是头布局或者底布局要记得return,否则会爆空指针异常。

下面是头部和底部点击的监听

public interface OnFootClickListener {
    void onClick(View view, int position);
}

public interface OnHeadClickListener {
    void onClick(View view, int position);
}

调用

RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);


 findViewById(R.id.chose).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(!chose){
                    chose=!chose;
                    recyclerView.setLayoutManager(new GridLayoutManager(TestActivity1.this,2));
                    recyclerView.getAdapter().notifyDataSetChanged();
                    wrapperAdapter.spanSize(recyclerView);
                }else{
                    chose=!chose;
                    recyclerView.setLayoutManager(new LinearLayoutManager(TestActivity1.this));
                    recyclerView.getAdapter().notifyDataSetChanged();
                }
            }
        });

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        //原始adapter
        MyAdapter dapter = new MyAdapter(getDatas(), this);
        //wrapper
        wrapperAdapter = new WrapperHeadAndFootAdapter(dapter);
        LayoutInflater layoutInflater = LayoutInflater.from(this);
        recyclerView.setAdapter(wrapperAdapter);

        wrapperAdapter.addHeadView(layoutInflater.inflate(R.layout.head_view,recyclerView,false));
        wrapperAdapter.addHeadView(layoutInflater.inflate(R.layout.head_view,recyclerView,false));
        wrapperAdapter.addFootView(layoutInflater.inflate(R.layout.head_view,recyclerView,false));
        wrapperAdapter.addFootView(layoutInflater.inflate(R.layout.head_view,recyclerView,false));
        //原始adapter的条目点击事件
        dapter.setOnItemClickListener(new OnItemClickListener<CharBean>() {
            @Override
            public void onItem(int position, CharBean charBean) {
                Toast.makeText(TestActivity1.this,charBean.getSrc(),Toast.LENGTH_SHORT).show();
            }
        });
        //底部监听事件
        wrapperAdapter.setOnFootClickListener(new OnFootClickListener() {
            @Override
            public void onClick(View view, int position) {
                wrapperAdapter.removeFootView(view,position);
            }
        });
        //头部监听事件
        wrapperAdapter.setOnHeadClickListener(new OnHeadClickListener() {
            @Override
            public void onClick(View view, int position) {
                wrapperAdapter.removeHeadView(view,position);
            }
        });

这样当然有点麻烦，我们可以封装成一个WrapperRecyclerView，例如这样

就可以欢快的调用了。

 @Override
    public void setAdapter(Adapter adapter) {
        if (mAdapter != null) {
            mAdapter.unregisterAdapterDataObserver(mDataObserver);
            mAdapter = null;
        }
        mAdapter = adapter;
        mAdapter.notifyDataSetChanged();
        mWrapperAdapter = new WrapperHeadAndFootAdapter(adapter,mHeads,mFoots);
        super.setAdapter(mWrapperAdapter);
        //适配GridLayoutManager
        mWrapperAdapter.spanSize(this);
        //注册监听器
        mWrapperAdapter.registerAdapterDataObserver(mDataObserver);
    }