学习通过Thread+Handler实现非UI线程更新UI组件

package cn.edu.bzu.asynchronous_processomg;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

/**
 * 学习通过Thread+Handler实现非UI线程更新UI组件
 * 学习异步加载的使用
 * @author monster
 *  date:2015-05-28
 *  introduce : Android只允许UI线程修改Activity里的UI组件
 *  Aim：点击按钮读取CSDN网站的LOGO
 */  
public class MainActivity extends Activity {
   private Button mButton;
   private ImageView mImageView; 
   
   private final static int MSG_SUCCESS = 0; //获取图片成功的标识
   private final static int MSG_FAILURE = 1; //获取图片失败的标识
   
   private Thread mThread;
   
   private Handler mHandler=new Handler(){
       public void handleMessage(Message msg){  //此方法在UI线程中运行
           switch(msg.what){
               case MSG_SUCCESS:
                   mImageView.setImageBitmap((Bitmap)msg.obj); //得到obj，并且强制类型转换成Bitmap类型--->>>obj含有图片的信息
                   Toast.makeText(getApplication(), "success", Toast.LENGTH_LONG).show();
                   break;    
               case MSG_FAILURE:
                   Toast.makeText(getApplication(), "error", Toast.LENGTH_LONG).show();
                   break;
           }
       }
       
   };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //实例化控件的时候，如果为当前上下文的时候，则不需要写上下文
        mButton=(Button)findViewById(R.id.mButton);
        mImageView=(ImageView)findViewById(R.id.mImageView);
        
        mButton.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View v) {
                if(mThread==null){
                    mThread=new Thread(runnable);
                    mThread.start();
                }
            }
        });
    }
            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"); //csdn 的logo
                    final Bitmap bm;
                    try {
                        HttpResponse hr=hc.execute(hg); // 响应做出的请求
                        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
                }
            };

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
    
}