Android 图片异步加载

ListView异步加载图片是非常实用的方法，凡是是要通过网络获取图片资源一般使用这种方法比较好，用户体验好，下面就说实现方法，先贴上主方法的代码： 
package cn.wangmeng.test;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;

public class AsyncImageLoader {

  private HashMap<String, SoftReference<Drawable>> imageCache;
   
      public AsyncImageLoader() {
       imageCache = new HashMap<String, SoftReference<Drawable>>();
      }
   
      public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {
          if (imageCache.containsKey(imageUrl)) {
              SoftReference<Drawable> softReference = imageCache.get(imageUrl);
              Drawable drawable = softReference.get();
              if (drawable != null) {
                  return drawable;
              }
          }
          final Handler handler = new Handler() {
              public void handleMessage(Message message) {
                  imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
              }
          };
          new Thread() {
              @Override
              public void run() {
                  Drawable drawable = loadImageFromUrl(imageUrl);
                  imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
                  Message message = handler.obtainMessage(0, drawable);
                  handler.sendMessage(message);
              }
          }.start();
          return null;
      }
   
  public static Drawable loadImageFromUrl(String url) {
   URL m;
   InputStream i = null;
   try {
    m = new URL(url);
    i = (InputStream) m.getContent();
   } catch (MalformedURLException e1) {
    e1.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
   Drawable d = Drawable.createFromStream(i, "src");
   return d;
  }
   
      public interface ImageCallback {
          public void imageLoaded(Drawable imageDrawable, String imageUrl);
      }

}

以上代码是实现异步获取图片的主方法，SoftReference是软引用，是为了更好的为了系统回收变量，重复的URL直接返回已有的资源，实现回调函数，让数据成功后，更新到UI线程。 
几个辅助类文件：
package cn.wangmeng.test;

public class ImageAndText {
     private String imageUrl;
     private String text;

     public ImageAndText(String imageUrl, String text) {
         this.imageUrl = imageUrl;
         this.text = text;
     }
     public String getImageUrl() {
         return imageUrl;
     }
     public String getText() {
         return text;
     }
}
package cn.wangmeng.test;

import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

public class ViewCache {

     private View baseView;
     private TextView textView;
     private ImageView imageView;

     public ViewCache(View baseView) {
         this.baseView = baseView;
     }

     public TextView getTextView() {
         if (textView == null) {
             textView = (TextView) baseView.findViewById(R.id.text);
         }
         return textView;
     }

     public ImageView getImageView() {
         if (imageView == null) {
             imageView = (ImageView) baseView.findViewById(R.id.image);
         }
         return imageView;
     }

}