自定义接口回调（外部接口）

理解：
① 创建一个回调接口ICallBack
② 让RecylerViewAdapter1持有回调接口，即回调接口对象并实例化，然后在别的方法中调用接口对象的方法
③ FirstActivity1调用该方法，重写接口方法

反过来理解：

person.setAge(int age); //普通方法
adapter.setOnItemClickListener(OnItemClickListener listener) //回调方法

person.setAge(int age){
     this.age=age;
}
public void setData(List list) {
        if (list != null) {
            mData.clear();
            mData.addAll(list);
            notifyDataSetChanged();
        }
}
public void setOnItemClickListener(OnItemClickListener listener) {
        mItemClickListener = listener;
}

FirstActivity调用该方法，只不过普通方法里的参数不是接口不需要重写接口中的方法，而setOnItemClickListener则需要重写。调用该方法并重写参数（接口）中的方法后，相当于初始化xxAdapter中的mItemClickListener不至于报空指针异常，雷同adapter中的setData()方法和setAge()方法。这样再在xxAdapter类中的其他方法中调用mItemClickListener.OnItemClick()方法即可，因为OnItemClick已经在FirstActivity1中重写并具体实现了。

private OnItemClickListener mItemClickListener;

public void setOnItemClickListener(OnItemClickListener listener) {
        mItemClickListener = listener;
    }

public interface OnItemClickListener {
        public void OnItemClick(View view, int position, T data);
    }

Java接口回调机制详解
详细的代码部分中的第2步：Boss的doEvent方法是老板说的话，即“打电话给我，告诉我已经完成工作了”

一个经典例子让你彻彻底底理解java回调机制

ICallBack

package com.example.recyclerview.callback2;

/**
 * Created by HASEE on 2017/6/28 10:18
 */

public interface ICallBack {
    void onClick();
}

RecylerViewAdapter1

package com.example.recyclerview.callback2;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.recyclerview.R;

import java.util.List;

/**
 * Created by HASEE on 2017/6/13 18:30
 */

public class RecylerViewAdapter1 extends RecyclerView.Adapter {

    private List list;
    private ICallBack iCallBack;

    public RecylerViewAdapter1(List list,ICallBack iCallBack) {
        this.list = list;
        this.iCallBack = iCallBack;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, null);
        MyViewHolder myViewHolder = new MyViewHolder(view);
        myViewHolder.textView = (TextView) view.findViewById(R.id.id_index_gallery_item_text);
        myViewHolder.imageView = (ImageView) view.findViewById(R.id.id_index_gallery_item_image);

        return myViewHolder;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        MyViewHolder myViewHolder = (MyViewHolder) holder;
        myViewHolder.textView.setText("小呆比");
        myViewHolder.imageView.setBackgroundResource(R.mipmap.ic_launcher);

        myViewHolder.imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                iCallBack.onClick();
            }
        });
    }

    @Override
    public int getItemCount() {
        return list.size();
    }


    class MyViewHolder extends RecyclerView.ViewHolder {

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

        TextView textView;
        ImageView imageView;
    }
}

FirstActivity1

package com.example.recyclerview.callback2;

import android.os.Bundle;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.widget.Toast;

import com.example.recyclerview.R;

import java.util.ArrayList;
import java.util.List;

import butterknife.Bind;
import butterknife.ButterKnife;

public class FirstActivity1 extends AppCompatActivity implements ICallBack {

    @Bind(R.id.recycleView)
    RecyclerView recycleView;
    @Bind(R.id.refresh)
    SwipeRefreshLayout refresh;
    RecylerViewAdapter1 recyclerViewAdapter;
    private List list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_first1);
        ButterKnife.bind(this);

        initData();
        //因为FirstActivity1实现了ICallBack接口，所以这里传入this
        recyclerViewAdapter = new RecylerViewAdapter1(list, this);
        recycleView.setLayoutManager(new GridLayoutManager(this, 3));
        recycleView.setAdapter(recyclerViewAdapter);


    }

    public void initData() {
        list = new ArrayList<>();
        list.add(R.mipmap.ic_launcher);
        list.add(R.mipmap.ic_launcher);
        list.add(R.mipmap.ic_launcher);
        list.add(R.mipmap.ic_launcher);
    }

    @Override
    public void onClick() {
        Toast.makeText(FirstActivity1.this, "点我的是傻逼hhhhhh", Toast.LENGTH_SHORT).show();
    }
}