android主线程和子线程之间消息传递详解

从主线程发送消息到子线程（准确地说应该是非ui线程）

package com.zhuozhuo;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.looper;
import android.os.message;
import android.util.log;
import android.view.view;
import android.view.view.onclicklistener;

public class looperthreadactivity extends activity{
 /** called when the activity is first created. */
 
 private final int msg_hello = 0;
 private handler mhandler;
 
 @override
 public void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.main);
  new customthread().start();//新建并启动customthread实例
  
  findviewbyid(r.id.send_btn).setonclicklistener(new onclicklistener() {
   
   @override
   public void onclick(view v) {//点击界面时发送消息
    string str = "hello";
    log.d("test", "mainthread is ready to send msg:" + str);
    mhandler.obtainmessage(msg_hello, str).sendtotarget();//发送消息到customthread实例
    
   }
  });
  
 }
 
 
 
 
 
 class customthread extends thread {
  @override
  public void run() {
   //建立消息循环的步骤
   looper.prepare();//1、初始化looper
   mhandler = new handler(){//2、绑定handler到customthread实例的looper对象
    public void handlemessage (message msg) {//3、定义处理消息的方法
     switch(msg.what) {
     case msg_hello:
      log.d("test", "customthread receive msg:" + (string) msg.obj);
     }
    }
   };
   looper.loop();//4、启动消息循环
  }
 }
}

从非ui线程传递消息到ui线程(界面主线程），因为主界面已经有messagequeue，所以可以直接获取消息处理消息。而上面由主线程向非ui线程中处理消息的时候，非ui线程需要先添加消息队列，然后处理消息循环。

public class threadhandleractivity extends activity {
 /** called when the activity is first created. */
 
 private static final int msg_success = 0;//获取图片成功的标识
 private static final int msg_failure = 1;//获取图片失败的标识
 
 private imageview mimageview;
 private button mbutton;
 
 private thread mthread;
 
 private handler mhandler = new handler() {
  public void handlemessage (message msg) {//此方法在ui线程运行
   switch(msg.what) {
   case msg_success:
    mimageview.setimagebitmap((bitmap) msg.obj);//imageview显示从网络获取到的logo
    toast.maketext(getapplication(), getapplication().getstring(r.string.get_pic_success), toast.length_long).show();
    break;

   case msg_failure:
    toast.maketext(getapplication(), getapplication().getstring(r.string.get_pic_failure), toast.length_long).show();
    break;
   }
  }
 };
 
 @override
 public void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.main);
  mimageview= (imageview) findviewbyid(r.id.imageview);//显示图片的imageview
  mbutton = (button) findviewbyid(r.id.button);
  mbutton.setonclicklistener(new onclicklistener() {
   
   @override
   public void onclick(view v) {
    if(mthread == null) {
     mthread = new thread(runnable);
     mthread.start();//线程启动
    }
    else {
     toast.maketext(getapplication(), getapplication().getstring(r.string.thread_started), toast.length_long).show();
    }
   }
  });
 }
 
 runnable runnable = new runnable() {
  
  @override
  public void run() {//run()在新的线程中运行
   httpclient hc = new defaulthttpclient();
   httpget hg = new httpget("http://csdnimg.cn/www/images/csdnindex_logo.gif");//获取csdn的logo
   final bitmap bm;
   try {
    httpresponse hr = hc.execute(hg);
    bm = bitmapfactory.decodestream(hr.getentity().getcontent());
   } catch (exception e) {
    mhandler.obtainmessage(msg_failure).sendtotarget();//获取图片失败
    return;
   }
   mhandler.obtainmessage(msg_success,bm).sendtotarget();//获取图片成功，向ui线程发送msg_success标识和bitmap对象

//   mimageview.setimagebitmap(bm); //出错！不能在非ui线程操作ui元素

//   mimageview.post(new runnable() {//另外一种更简洁的发送消息给ui线程的方法。
//    
//    @override
//    public void run() {//run()方法会在ui线程执行
//     mimageview.setimagebitmap(bm);
//    }
//   });
  }
 };

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