消息传递之接口回调

Android实现消息传递的基本方式有三种，分别是广播消息、Handler线程间通信、接口回调，这几种方法都是最基本的，现在GitHub上可能还有一些像EventBus等优秀的事件传递框架，既可以降低程序的耦合性，又可以更加方便优雅的进行消息的传递，今天通过一些小案例，举例一下接口回调在开发中的应用。

现在考虑这样一个场景，一个列表，点击列表的不同Item，然后获取Item的相关信息进行显示，或者执行别的业务逻辑均可，就是说要把Adapter中的点击事件传递到Activity中，然后接到消息后在Activity中执行一些别的业务逻辑。

定义接口

package com.example.toby.myapplication;

/**
 * author : toby
 * e-mail : 13128826083@163.com
 * time : 2018/6/20
 * desc :
 */

public interface OnItemClicked {

    void showMessage(int index);

}

在Activity中实现接口

private class OnItemClickedIml implements OnItemClicked {
        @Override
        public void showMessage(int index) {
            Toast.makeText(ListViewActivity.this, dataList.get(index), Toast.LENGTH_SHORT).show();
            Log.d("------>", "----showMessage-->" + dataList.get(index));
        }
    }

Adapter中的相关代码

package com.example.toby.myapplication;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.List;

/**
 * author : toby
 * e-mail : 13128826083@163.com
 * time : 2018/6/20
 * desc :
 */

public class MyAdapter extends BaseAdapter {

    private Context context;
    private List<String> dataList;
    private OnItemClicked onItemClicked;

    public MyAdapter(Context context, List<String> dataList, OnItemClicked onItemClicked) {
        this.context = context;
        this.dataList = dataList;
        this.onItemClicked = onItemClicked;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public int getCount() {
        return dataList.size();
    }

    @Override
    public Object getItem(int position) {
        return dataList.get(position);
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder = null;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.item_list_view_layout, null);
            viewHolder = new ViewHolder();
            viewHolder.layoutItem = convertView.findViewById(R.id.layoutItem);
            viewHolder.txtView = convertView.findViewById(R.id.txtView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.txtView.setText(dataList.get(position));
        viewHolder.layoutItem.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onItemClicked.showMessage(position);
            }
        });
        return convertView;
    }

    protected static class ViewHolder {
        LinearLayout layoutItem;
        TextView txtView;
    }

}

初始化Adapter与ListView，并将接口的引用传递给Adapter，然后在Adapter中的点击事件中调用接口方法，并把相关的参数position传递进来。

package com.example.toby.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;

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

public class ListViewActivity extends AppCompatActivity {

    private ListView listView;
    private MyAdapter adapter;
    private List<String> dataList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_view);
        listView = findViewById(R.id.listView);
        initData();
    }

    private void initData() {
        if (dataList == null) {
            dataList = new ArrayList<>();
        } else {
            dataList.clear();
        }
        for (int i = 0; i < 20; i++) {
            dataList.add("长河老表" + i);
        }
        adapter = new MyAdapter(this, dataList, new OnItemClickedIml());
        listView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
    }

    private class OnItemClickedIml implements OnItemClicked {
        @Override
        public void showMessage(int index) {
            Toast.makeText(ListViewActivity.this, dataList.get(index), Toast.LENGTH_SHORT).show();
            Log.d("------>", "----showMessage-->" + dataList.get(index));
        }
    }

}

这样一来，点击ListView的相关Item后，在Adapter通过即接口回调把点击事件及相关参数回传到Activity中的接口实现就已经完成了。