Android 异步从网络上下载图片

package com.example.android_asynctask;

import org.apache.http.HttpEntity;
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 org.apache.http.util.EntityUtils;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {

    private Button button;
    private ImageView imageView;
    private String image_Path = "http://e.hiphotos.baidu.com/image/pic/item/2fdda3cc7cd98d10b510fdea233fb80e7aec9021.jpg";
    private ProgressDialog dialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.button1);
        imageView = (ImageView) findViewById(R.id.imageView1);
        dialog = new ProgressDialog(this);
        dialog.setTitle("提示信息");
        dialog.setMessage("正在下载，请稍候...");
        button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                new MYTask().execute(image_Path);
            }
        });
    }

    /**
     * 使用异步任务的规则： 1、申明的类继承AsyncTask 标注三个参数的类型
     * 2、第一个参数表示要执行的任务，通常是网络的路径；第二个参数表示进度的刻度，第三个参数表示任务执行的返回结果
     * 
     * @author liende
     * 
     */
    public class MYTask extends AsyncTask<String, Void, Bitmap> {
        /**
         * 表示任务执行之前的操作
         */
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            dialog.show();
        }

        /**
         * 主要是完成耗时的操作
         */
        @Override
        protected Bitmap doInBackground(String... arg0) {
            // TODO Auto-generated method stub
            // 使用网络连接类HttpClient类王城对网络数据的提取
            HttpClient httpClient = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(arg0[0]);
            Bitmap bitmap = null;
            try {
                HttpResponse httpResponse = httpClient.execute(httpGet);
                if (httpResponse.getStatusLine().getStatusCode() == 200) {
                    HttpEntity httpEntity = httpResponse.getEntity();
                    byte[] data = EntityUtils.toByteArray(httpEntity);
                    bitmap = BitmapFactory
                            .decodeByteArray(data, 0, data.length);
                }
            } catch (Exception e) {
                // TODO: handle exception
            }
            return bitmap;
        }

        /**
         * 主要是更新UI的操作
         */
        @Override
        protected void onPostExecute(Bitmap result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            imageView.setImageBitmap(result);
            dialog.dismiss();
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}