Android 異步從網絡上下載圖片

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("正在下載，請稍候...");
        button.setOnClickListener(new View.OnClickListener() {

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

    /**
     * 使用異步任務的規則： 1、申明的類繼承AsyncTask 標注三個參數的類型
     * 2、第一個參數表示要執行的任務，通常是網絡的路徑；第二個參數表示進度的刻度，第三個參數表示任務執行的返回結果
     * 
     * @author liende
     * 
     */
    public class MYTask extends AsyncTask<String, Void, Bitmap> {
        /**
         * 表示任務執行之前的操作
         */
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            dialog.show();
        }

        /**
         * 主要是完成耗時的操作
         */
        @Override
        protected Bitmap doInBackground(String... arg0) {
            // TODO Auto-generated method stub
            // 使用網絡連接類HttpClient類王城對網絡數據的提取
            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;
    }

}


<uses-permission android:name="android.permission.INTERNET" />