Android 多线程：使用Thread和Handler (从网络上获取图片)

package com.xsjayz.thread;

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

/**
* 使用Thread+Handler的方式实现在非UI线程发送消息通知UI线程更新界面
*
* <a href="http://my.oschina.net/arthor" class="referer" target="_blank">@author</a>  XuShaoJie
* @version 2012-08-31
*/
public class ThreadHandlerActivity extends Activity {

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;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

mImageView = (ImageView) findViewById(R.id.imageView);
mButton = (Button) findViewById(R.id.button);

mButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// 如果线程还没启动，则启动新的线程
if (mThread == null) {
mThread = new Thread(runnable);
mThread.start();

// 否则提示："线程已经启动"
} else {
Toast.makeText(
getApplication(),
getApplication().getString(R.string.thread_started),
Toast.LENGTH_LONG).show();
}
}
});
}

private Handler mHandler = new Handler() {
// 重写handleMessage()方法，此方法在UI线程运行
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
// 如果成功，则显示从网络获取到的图片
case MSG_SUCCESS:
mImageView.setImageBitmap((Bitmap) msg.obj);
Toast.makeText(getApplication(),
getApplication().getString(R.string.get_pic_success),
Toast.LENGTH_LONG).show();
break;
// 否则提示失败
case MSG_FAILURE:
Toast.makeText(getApplication(),
getApplication().getString(R.string.get_pic_failure),
Toast.LENGTH_LONG).show();
break;
}
}
};

Runnable runnable = new Runnable() {
// 重写run()方法，此方法在新的线程中运行
@Override
public void run() {
HttpClient httpClient = new DefaultHttpClient();
// 从网络上获取图片
HttpGet httpGet = new HttpGet(
"http://www.oschina.net/img/logo.gif");
final Bitmap bitmap;
try {
HttpResponse httpResponse = httpClient.execute(httpGet);
// 解析为图片
bitmap = BitmapFactory.decodeStream(httpResponse.getEntity()
.getContent());
} catch (Exception e) {
mHandler.obtainMessage(MSG_FAILURE).sendToTarget();// 获取图片失败
return;
}

// 获取图片成功，向UI线程发送MSG_SUCCESS标识和bitmap对象
mHandler.obtainMessage(MSG_SUCCESS, bitmap).sendToTarget();
}
};

}