给recycleview加headview

参考了https://blog.csdn.net/qibin0506/article/details/49716795

由于recycleview没有直接添加头部view的api，所以需要我们自己去添加，下面贴上代码

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

    public static final int TYPE_HEADER = 0;
    public static final int TYPE_NORMAL = 1;

    private ArrayList<String> mDatas = new ArrayList<>();

    private View mHeaderView;

    private OnItemClickListener mListener;

    public void setOnItemClickListener(OnItemClickListener li) {
        mListener = li;
    }

    public void setHeaderView(View headerView) {
        mHeaderView = headerView;
        notifyItemInserted(0);
    }

    public View getHeaderView() {
        return mHeaderView;
    }

    public void addDatas(ArrayList<String> datas) {
        mDatas.addAll(datas);
        notifyDataSetChanged();
    }

    @Override
    public int getItemViewType(int position) {
        if(mHeaderView == null) return TYPE_NORMAL;
        if(position == 0) return TYPE_HEADER;
        return TYPE_NORMAL;
    }

//此方法确保网格布局时头部item占据一整行
    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
        RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
        if(manager instanceof GridLayoutManager) {
            final GridLayoutManager gridManager = ((GridLayoutManager) manager);
            gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                @Override
                public int getSpanSize(int position) {
                    return getItemViewType(position) == TYPE_HEADER
                            ? gridManager.getSpanCount() : 1;
                }
            });
        }
    }

    @Override
    public void onViewAttachedToWindow(RecyclerView.ViewHolder holder) {
        super.onViewAttachedToWindow(holder);
        ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
        if(lp != null
                && lp instanceof StaggeredGridLayoutManager.LayoutParams) {
            StaggeredGridLayoutManager.LayoutParams p = (StaggeredGridLayoutManager.LayoutParams) lp;
            p.setFullSpan(holder.getLayoutPosition() == 0);
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if(mHeaderView != null && viewType == TYPE_HEADER) return new Holder(mHeaderView);
        View layout = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
        return new Holder(layout);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
        if(getItemViewType(position) == TYPE_HEADER) return;

        final int pos = getRealPosition(viewHolder);
        final String data = mDatas.get(pos);
        if(viewHolder instanceof Holder) {
            ((Holder) viewHolder).text.setText(data);
            if(mListener == null) return;
            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    mListener.onItemClick(pos, data);
                }
            });
        }
    }

    public int getRealPosition(RecyclerView.ViewHolder holder) {
        int position = holder.getLayoutPosition();
        return mHeaderView == null ? position : position - 1;
    }

    @Override
    public int getItemCount() {
        return mHeaderView == null ? mDatas.size() : mDatas.size() + 1;
    }

    class Holder extends RecyclerView.ViewHolder {

        TextView text;

        public Holder(View itemView) {
            super(itemView);
            if(itemView == mHeaderView) return;
            text =  itemView.findViewById(R.id.text);
        }
    }

    interface OnItemClickListener {
        void onItemClick(int position, String data);
    }
}

public class MainActivity extends AppCompatActivity {
    RecyclerView mRecyclerView;
    LinearLayoutManager mLayoutManager;
    MyAdapter mAdapter;
    ArrayList<String> list;
    Button bt;
    View header;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mRecyclerView = (RecyclerView) findViewById(R.id.list);
        bt = findViewById(R.id.bt);

       // mLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
        mLayoutManager = new GridLayoutManager(this, 2);
        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setItemAnimator(new DefaultItemAnimator());

        mAdapter = new MyAdapter();
        mRecyclerView.setAdapter(mAdapter);
        mAdapter.addDatas(generateData());
        setHeader(mRecyclerView);
        mAdapter.setOnItemClickListener(new MyAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(int position, String data) {
                Toast.makeText(MainActivity.this, data, Toast.LENGTH_SHORT).show();
            }
        });

        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this, "你点击了头部", Toast.LENGTH_SHORT).show();
            }
        });

    }

    private void setHeader(RecyclerView view) {
        header = LayoutInflater.from(this).inflate(R.layout.header, view, false);
        bt = header.findViewById(R.id.bt);
        mAdapter.setHeaderView(header);
    }

    private ArrayList<String> generateData() {
        list = new ArrayList<>();
        list.clear();
        for (int i = 0; i < 30; i++) {
            list.add("" + i);
        }
        return list;
    }
}

<!--这是recycleview的item-->

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="36dp">
    <TextView
        android:id="@+id/text"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center" />
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="36dp"
    android:orientation="horizontal">
<!--这是headview的布局-->
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="我是头部啊" />

    <View
        android:layout_width="100dp"
        android:layout_height="match_parent" />

    <Button
        android:id="@+id/bt"
        android:layout_width="80dp"
        android:layout_height="match_parent"
        android:text="点我" />
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

 <android.support.v7.widget.RecyclerView
     android:id="@+id/list"
     android:layout_width="match_parent"
     android:layout_height="match_parent">

 </android.support.v7.widget.RecyclerView>
</android.support.constraint.ConstraintLayout>