前言

最近碰到了RecyclerView展开折叠的需求。
在CSDN上看到了一种写法是在RecyclerView的Item布局外面嵌套了一层LinearLayout。
但是这样子做有一个不好的地方是需要取消RecyclerView的重用机制。
后来又在同事的建议下尝试了只使用一层RecyclerView来实现展开折叠的实现方式。
本文会把两种写法都记录下来，大家可以直接去看第二种实现方式。
毕竟从性能等方面来考虑，只用一层RecyclerView无疑是最优解。

（于2017.11.26更新，提供了单层RecyclerView实现点击展开/折叠的带数据加载、移除的写法。）
（于2017.12.26更新，修改github指向地址。增加首发说明。）

本文由作者三汪首发于简书。
本文demo已上传Github→戳这里

一、嵌套实现

1.要点说明

• 要记得在onCreateViewHolder()中取消Recycler的重用机制viewHolder.setIsRecyclable(false); 否则会出现重复添加子布局和在未点击展开时展开子布局的情况。
• 代码中使用了item外嵌套的LinearLayout的setTag()、getTag()来判断当前点击要触发的动作是展开还是折叠。当item离开当前屏幕时就会被销毁，因此Tag的值也就不存在了。

2.代码展示(仅展示主要代码)

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private Button button;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = (RecyclerView) findViewById(R.id.recycler_main);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        MainRecyclerViewAdapter recyclerAdapter = new MainRecyclerViewAdapter();
        recyclerView.setAdapter(recyclerAdapter);

        button = (Button) findViewById(R.id.button_main);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,TwoActivity.class);
                startActivity(intent);
            }
        });
    }
}

MainRecyclerViewAdapter.java

public class MainRecyclerViewAdapter extends RecyclerView.Adapter<MainRecyclerViewAdapter.MainRecyclerViewHolder> {


    @Override
    public MainRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View item = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler,parent,false);
        MainRecyclerViewHolder viewHolder = new MainRecyclerViewHolder(item);
        viewHolder.setIsRecyclable(false);//取消viewHolder的重用机制。没有这句话子布局subView会被重复添加。

        return viewHolder;
    }

    @Override
    public void onBindViewHolder(MainRecyclerViewHolder holder, int position) {

    }

    @Override
    public int getItemCount() {
        return 20;
    }


    protected class MainRecyclerViewHolder extends RecyclerView.ViewHolder {

        private TextView textTime, textPrice;

        public MainRecyclerViewHolder(View itemView) {
            super(itemView);
            textTime = itemView.findViewById(R.id.text_first_time);
            textPrice = itemView.findViewById(R.id.text_first_price);
            //item点击事件监听
            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    int flag = 1;//用于判断当前是展开还是收缩状态
                    //获取外层linearlayout布局
                    LinearLayout linearLayout = view.findViewById(R.id.main_tree_root_layout);
                    //new一个RecyclerView来当展开的子布局。
                    RecyclerView subView = new RecyclerView(view.getContext());
                    SubViewAdapter adapter = new SubViewAdapter();
                    subView.setLayoutManager(new LinearLayoutManager(view.getContext()));
                    subView.setAdapter(adapter);
                    //当flag不为空的时候,获取flag的值。
                    if (linearLayout.getTag() != null) {
                        flag = (int) linearLayout.getTag();
                    }
                    //当flag为1时，添加子布局。否则，移除子布局。
                    if (flag == 1) {
                        linearLayout.addView(subView);
                        subView.setTag(101);
                        linearLayout.setTag(2);
                    } else {
                        linearLayout.removeView(view.findViewWithTag(101));
                        linearLayout.setTag(1);
                    }
                }
            });
        }
    }

    //subView的adapter
    private class SubViewAdapter extends RecyclerView.Adapter{

        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            return new SubViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler_detail,parent,false));
        }

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

        }

        @Override
        public int getItemCount() {
            return 5;
        }

        private class SubViewHolder extends RecyclerView.ViewHolder{
            private SubViewHolder(View itemView){
                super(itemView);
            }
        }
    }
}

二、单层RecyclerView实现

1.要点说明

• 当前写法采用了两个SparseArray来分别保存第一级布局和第二级布局的数据对象。
• 第一级布局的数据对象中增加了isExpand字段来标志当前布局是否被点击展开过，以及增加了addedSubNum字段来储存点击展开后新增的item个数。
• 点击折叠移除数据时，由于SparseArray的特性，必须使用一个新的SparseArray来作为中转，暂时保存需要修改key的数据。等remove动作做完以后再重新put回原来的SparseArray。

2.代码展示(仅展示主要代码)

TheFirstBean.java

/**
 * 第一层布局数据bean
 * Created by 2dog on 2017/11/26.
 */

public class TheFirstBean {
    private boolean isExpand = false;
    private int addedSubNum;

    public TheFirstBean() {
    }

    public void setExpand(boolean expand) {

        isExpand = expand;
    }

    public void setAddedSubNum(int addedSubNum) {
        this.addedSubNum = addedSubNum;
    }

    public boolean isExpand() {
    
        return isExpand;
    }

    public int getAddedSubNum() {
        return addedSubNum;
    }
}

TwoActivity.java

public class TwoActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_two);
        //数据初始化
        List<TheFirstBean> list = new ArrayList<>();
        for (int i = 0; i<20;i++){
            list.add(new TheFirstBean());
        }
        //设置RecyclerView
        recyclerView = (RecyclerView) findViewById(R.id.recycler_two);
        recyclerView.setAdapter(new TwoRecyclerViewAdapter(list));
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
    }

}

TwoRecyclerViewAdapter .java

/**
 * 使用一层recyclerView实现点击展开二层布局效果
 * Created by wolfgy on 2017/10/16.
 */

public class TwoRecyclerViewAdapter  extends RecyclerView.Adapter {

    private SparseArray<TheFirstBean> firstBeanSparseArray = new SparseArray<>();//存储每日流水数据
    private SparseArray<TheSecondBean> secondBeanSparseArray = new SparseArray<>();//存储每条流水数据
    private static final int TYPE_FIRST = 0;//第一层布局
    private static final int TYPE_SECOND = 1;//第二层布局

    public TwoRecyclerViewAdapter(List<TheFirstBean> list) {
        for (int i=0;i<list.size();i++){
            firstBeanSparseArray.put(i,list.get(i));
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //根据ViewType实例化布局
        switch (viewType){
            case TYPE_FIRST:
                return new FirstViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler,parent,false));
            case TYPE_SECOND:
                return new FirstViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler_detail,parent,false));
        }
        return new FirstViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler,parent,false));
    }

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

    }

    @Override
    public int getItemCount() {
        return firstBeanSparseArray.size()+secondBeanSparseArray.size();
    }

    @Override
    public int getItemViewType(int position) {
        if (secondBeanSparseArray.get(position) != null){
            return TYPE_SECOND;
        }
        return TYPE_FIRST;
    }

    private class FirstViewHolder extends RecyclerView.ViewHolder{

        public FirstViewHolder(final View itemView) {
            super(itemView);
            //item点击事件监听
            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (firstBeanSparseArray.get(getLayoutPosition()).isExpand()){
                        //设置第二级布局是否展开的flag
                        firstBeanSparseArray.get(getLayoutPosition()).setExpand(false);
                        //获取要移除的第二级布局个数
                        int addedSubNum = firstBeanSparseArray.get(getLayoutPosition()).getAddedSubNum();
                        //移除第二级布局
                        removeItems(getLayoutPosition(),addedSubNum);
                        notifyItemRangeRemoved(getLayoutPosition()+1,addedSubNum);
                    }else{
                        //设置第二级布局是否展开的flag
                        firstBeanSparseArray.get(getLayoutPosition()).setExpand(true);
                        //加载数据并获取载入的第二级布局个数
                        List<TheSecondBean> list = new ArrayList<>();
                        for (int i =0;i<5;i++){
                            list.add(new TheSecondBean());
                        }
                        int addedSubNum = setEachFlows(getLayoutPosition(),list);
                        //添加第二级布局
                        firstBeanSparseArray.get(getLayoutPosition()).setAddedSubNum(addedSubNum);
                        notifyItemRangeInserted(getLayoutPosition()+1,addedSubNum);
                    }

                }
            });
        }
    }

    private class SecondViewHolder extends RecyclerView.ViewHolder{

        public SecondViewHolder(View itemView) {
            super(itemView);
        }
    }


    /**
     * 点击展开时加载相应数据
     * @param parentPosition
     * @param list
     * @return
     */
    public int setEachFlows(int parentPosition , List<TheSecondBean> list) {

        //更新position大于当前点击的position的第一级布局的item的position
        for (int i = getItemCount()-1 ; i > parentPosition ; i-- ){
            int index = firstBeanSparseArray.indexOfKey(i);
            if (index<0){
                continue;
            }
            TheFirstBean dailyFlow = firstBeanSparseArray.valueAt(index);
            firstBeanSparseArray.removeAt(index);
            firstBeanSparseArray.put(list.size()+i,dailyFlow);
        }
        //更新position大于当前点击的position的第二级布局的item的position
        for (int i = getItemCount()-1 ; i > parentPosition ; i-- ){
            int index = secondBeanSparseArray.indexOfKey(i);
            if (index<0){
                continue;
            }
            TheSecondBean eachFlow = secondBeanSparseArray.valueAt(index);
            secondBeanSparseArray.removeAt(index);
            secondBeanSparseArray.append(list.size()+i,eachFlow);
        }
        //把获取到的数据根据相应的position放入SparseArray中。
        for (int i = 0 ;i < list.size() ; i++ ){
            secondBeanSparseArray.put(parentPosition+i+1,list.get(i));
        }
        return list.size();
    }

    /**
     * 点击折叠时移除相应数据
     * @param clickPosition
     * @param addedSubNum
     */
    private void removeItems(int clickPosition,int addedSubNum){
        //更新position大于当前点击的position的第一级布局item的position
        SparseArray<TheFirstBean> temp = new SparseArray();
        for (int i = getItemCount()-1 ; i > clickPosition+addedSubNum ; i-- ){
            int index = firstBeanSparseArray.indexOfKey(i);
            if (index<0){
                continue;
            }
            TheFirstBean dailyFlow = firstBeanSparseArray.valueAt(index);
            firstBeanSparseArray.removeAt(index);
            temp.put(i-addedSubNum,dailyFlow);
        }
        for (int i=0;i<temp.size();i++ ){

            int key = temp.keyAt(i);
            firstBeanSparseArray.put(key,temp.get(key));
        }
        //更新position大于当前点击的position的第二级布局item的position
        SparseArray<TheSecondBean> temp2 = new SparseArray();
        for (int i = getItemCount()-1 ; i > clickPosition+addedSubNum ; i-- ){
            int index = secondBeanSparseArray.indexOfKey(i);
            if (index<0){
                continue;
            }
            TheSecondBean eachFlow = secondBeanSparseArray.valueAt(index);
            secondBeanSparseArray.removeAt(index);
            temp2.put(i-addedSubNum,eachFlow);
        }
        for (int i = 1; i <= addedSubNum; i++) {
            //移除被折叠的第二级布局数据
            secondBeanSparseArray.remove(clickPosition+i);
        }
        for (int i=0;i<temp2.size();i++ ){

            int key = temp2.keyAt(i);
            secondBeanSparseArray.put(key,temp2.get(key));
        }
    }

}

以上。
希望我的文章对你能有所帮助。
我不能保证文中所有说法的百分百正确，但我能保证它们都是我的理解和感悟以及拒绝复制黏贴。
有什么意见、见解或疑惑，欢迎留言讨论。