android主线程和子线程之间消息传递详解

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  } }}

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);//    }//   });  } };