Android实现图片异步加载操作

/** 
* User: Tom 
* Date: 13-5-13 
* Time: 下午8:07 
*/ 
public class AsnycImageLoader { 

//定义一个HashMap进行存放缓存的Image key为String Value为一个弱引用的一个资源文件 
// 图片 为了方便JAVA的回收 
private Map<String, SoftReference<Drawable>> imageCache = null; 
public AsnycImageLoader() { 
imageCache = new HashMap<String, SoftReference<Drawable>>(); 
} 

/** 
* 加载图片 
* <p>imageurl为下载资源的URL， 
* ImageCallback当缓存中不存在相关图片时时行网络下载 
* 在多线程下要使用Handler进行操作UI 利用回调接口的方式进行更新UI 
* </p> 
* @param imageUrl 
* @param callback 
* @return 
*/ 
public Drawable loadDrawable(final String imageUrl, final ImageCallback callback) { 
//进行判断ImageCache中是否存在缓存图片 
if (imageCache.containsKey(imageUrl)) { 
SoftReference<Drawable> softReference = imageCache.get(imageUrl); 
if (softReference.get() != null) { 
return softReference.get(); 
} 
} 
//定义操作UI的Handler 
final Handler handler = new Handler() { 
@Override 
public void handleMessage(Message msg) { 
callback.imageLoaded((Drawable) msg.obj); 
} 
}; 

new Thread(new Runnable() { 
@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; 
} 

//根据URL地址进行获取资源 
protected Drawable loadImageFromUrl(String imageUrl) { 
try { 
return Drawable.createFromStream(new URL(imageUrl).openStream(), "src"); 
} catch (Exception e) { 
throw new RuntimeException(); 
} 
} 

//回调接口 
public interface ImageCallback { 
public abstract void imageLoaded(Drawable drawable); 
} 
}

/** 
* User: Tom 
* Date: 13-5-13 
* Time: 下午8:33 
*/ 
public class LoadImage extends Activity { 
private AsnycImageLoader loader = null; 

public void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.loadimages); 

loader = new AsnycImageLoader(); 

loadImage("http://www.jb51.net/images/icon-partners.png", R.id.image1); 
loadImage("http://www.jb51.net/images/icon-dev.png", R.id.image2); 
loadImage("http://pic28.jb51.net/20130421/12302174_231210305323_2.jpg", R.id.image3); 

} 

public void loadImage(String url, int id) { 
final ImageView imageView = (ImageView) findViewById(id); 
Drawable cacheImage = loader.loadDrawable(url, new AsnycImageLoader.ImageCallback() { 
@Override 
public void imageLoaded(Drawable drawable) { 
imageView.setImageDrawable(drawable); 
} 
}); 
if (cacheImage != null) { 
imageView.setImageDrawable(cacheImage); 
} 
} 
}