Android 利用 AsyncTask 异步读取网络图片

1.新建Android工程AsyncLoadPicture

新建布局文件activity_main.xml主界面为一个GridView，还有其子项布局文件gridview_item.xml

2.功能主界面MainActivity.java,主代码如下

 package com.example.asyncloadpicture;

 import java.util.ArrayList;

 import android.app.Activity;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.widget.GridView;

 /**
  * @author ymw
  * @data 2014-12-03
  */
 public class MainActivity extends Activity {

     private GridView gridViewImg;
     private ArrayList<ImageEntity> imageList = new ArrayList<ImageEntity>();

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);

         gridViewImg = (GridView) findViewById(R.id.gridViewImg);
         initData();
     }

     private void initData() {
         for (int i = 0; i < 15; i++) {
             ImageEntity b = new ImageEntity();
             b.setImage(BitmapFactory.decodeResource(getResources(),
                     R.drawable.nopicture));

             imageList.add(b);
         }

         ImageAdapter adapter = new ImageAdapter(getApplicationContext(),
                 imageList);
         gridViewImg.setAdapter(adapter);
         String[] params = {
                 "https://images0.cnblogs.com/i/169207/201408/112229149526951.png",
                 "p2" };
         new ImageLoadTask(getApplicationContext(), adapter).execute(params);
     }

     /** 图片异步加载类 */
     public class ImageLoadTask extends AsyncTask<String, Void, Void> {
         private ImageAdapter adapter;

         public ImageLoadTask(Context context, ImageAdapter adapter) {
             this.adapter = adapter;
         }

         @Override
         protected Void doInBackground(String... params) {
             String url = params[0];// 获取传来的参数，图片uri地址
             String p2 = params[1];
             for (int i = 0; i < adapter.getCount(); i++) {
                 ImageEntity bean = (ImageEntity) adapter.getItem(i);
                 Bitmap bitmap = BitmapFactory.decodeStream(Request
                         .HandlerData(url));
                 bean.setImage(bitmap);
                 publishProgress(); // 通知去更新UI
             }

             return null;
         }

         public void onProgressUpdate(Void... voids) {
             if (isCancelled())
                 return;
             // 更新UI
             adapter.notifyDataSetChanged();
         }
     }

     /** 图片实体 */
     public class ImageEntity {
         private Bitmap image;

         public Bitmap getImage() {
             return image;
         }

         public void setImage(Bitmap image) {
             this.image = image;
         }

     }
 }

3.GridView列表图片适配器代码ImageAdapter.java

 package com.example.asyncloadpicture;

 import java.util.ArrayList;

 import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.BaseAdapter;
 import android.widget.ImageView;

 import com.example.asyncloadpicture.MainActivity.ImageEntity;

 /**
  *
  * @author ymw
  * @data 2014-12-03 图片适配器
  */
 public class ImageAdapter extends BaseAdapter {

     private Context _context;
     private ArrayList<ImageEntity> _list;

     public ImageAdapter(Context context, ArrayList<ImageEntity> imageList) {
         this._context = context;
         this._list = imageList;
     }

     @Override
     public int getCount() {
         return _list.size();
     }

     @Override
     public Object getItem(int position) {
         return _list.get(position);
     }

     @Override
     public long getItemId(int position) {
         return position;
     }

     @Override
     public View getView(int position, View convertView, ViewGroup parent) {
         LayoutInflater inflater = LayoutInflater.from(_context);
         convertView = inflater.inflate(R.layout.gridview_item, null);

         ImageView imgView = (ImageView) convertView.findViewById(R.id.imgView);
         ImageEntity b = _list.get(position);
         // 如果有图片则读取，没有则跳过
         if (b.getImage() != null) {
             imgView.setImageBitmap(b.getImage());
         }
         return convertView;
     }
 }

4.请求网络读取图片的类Request.java

 package com.example.asyncloadpicture;

 import java.io.IOException;
 import java.io.InputStream;
 import java.net.URL;
 import java.net.URLConnection;

 import android.graphics.drawable.Drawable;
 import android.util.Log;

 /**
  * 工具类，主要根据url读取图片返回流的方法
  *
  * @author ymw
  *
  */
 public class Request {
     public static InputStream HandlerData(String url) {
         InputStream inStream = null;

         try {
             URL feedUrl = new URL(url);
             URLConnection conn = feedUrl.openConnection();
             conn.setConnectTimeout(10 * 1000);
             inStream = conn.getInputStream();
         } catch (Exception e) {
             e.printStackTrace();
         }

         return inStream;
     }

     /** 直接返回Drawable对象设置图片 */
     public static Drawable loadImageFromNetwork(String imageUrl) {
         Drawable drawable = null;
         try {
             // 可以在这里通过文件名来判断，是否本地有此图片
             drawable = Drawable.createFromStream(
                     new URL(imageUrl).openStream(), "image.jpg");
         } catch (IOException e) {
             Log.d("test", e.getMessage());
         }
         if (drawable == null) {
             Log.d("test", "null drawable");
         } else {
             Log.d("test", "not null drawable");
         }

         return drawable;
     }
 }

5.代码实例如下链接：

http://files.cnblogs.com/_ymw/AsyncLoadPicture_%E5%8D%9A%E5%AE%A2%E9%99%84%E4%BB%B6.rar