有主线程发送message给子线程

　　通常我们在处理耗时任务时候都会通过新建线程来处理，当任务处理完后通过Handler将结果发送回主线程。比如下面示例：

 package com.example.testlistener;

 import java.util.Timer;

 import java.util.TimerTask;

 import android.app.Activity;

 import android.content.res.Configuration;

 import android.os.Bundle;

 import android.os.Handler;

 import android.os.Message;

 import android.view.View;

 import android.view.View.OnClickListener;

 import android.view.View.OnLongClickListener;

 import android.widget.Button;

 import android.widget.EditText;

 import android.widget.Toast;

 public class MainActivity extends Activity {

     EditText txt;

     final Handler hander = new Handler(){

         public void handleMessage(android.os.Message msg) {

             if(msg.what == 0x1234){

                 Toast.makeText(MainActivity.this, msg.arg1 + "", 1000).show();

             }

         };

     };

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         new Timer().schedule(new TimerTask() {

             int i = 0;

             @Override

             public void run() {

                 i++;

                 Message msg = new Message();

                 msg.what = 0x1234;

                 msg.arg1 = i;

                 hander.sendMessage(msg);

             }

         }, 0, 2000);

     }

 }

　　那么，我们能不能通过Handler从主线程发送消息给子线程呢？答案是肯定的，需要用到Looper.prepare()和Looper.loop()。如下面的代码：

 public class MainActivity extends Activity {

     EditText txt;

     Button bt;

     TestThread testThread;

     int j = 0;

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         txt = (EditText) findViewById(R.id.txt);

         bt = (Button) findViewById(R.id.bn);

         testThread = new TestThread();

         testThread.start();

         bt.setOnClickListener(new OnClickListener() {

             @Override

             public void onClick(View arg0) {

                 j++;

                 Message msg = new Message();

                 msg.what = 0x1000;

                 msg.arg1 = j;

                 testThread.thander.sendMessage(msg);

             }

         });

     }

     //自定义子线程

     class TestThread extends Thread{

         public Handler thander;

         @Override

         public void run() {

             //创建一个Looper对象

             Looper.prepare();

             thander = new Handler(){

                 @Override

                 public void handleMessage(Message msg) {

                     if(msg.what == 0x1000){

                         System.out.println("j = " + msg.arg1);

                         //txt.setText(msg.arg1 + "");

                     }

                 }

             };

             //启动Looper

             Looper.loop();

         }

     }

 }

巴特西

有主线程发送message给子线程

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