ListView异步加载图片

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：
Java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);