下载图片过多溢出内存问题

过去一段时间一直有人和我说下载图片太多有时候会溢出内存 问我有啥办法，我说我也不知道除了把照片像素 参数缩小该一下，今天看源码的时候看见了SoftReference这个东西，我不知道干啥用的搜索了一下就是为了内存问题而应用的，而且好多地方用到了，我把他取出来弄了一下下载照片处理的方法，不过是handler处理的，如果用asn处理会更好一些吧

public DrawableManager() { 
    drawableMap = new HashMap<String, SoftReference<Drawable>>(); 
} 
 
public Drawable fetchDrawable(String urlString) { 
    SoftReference<Drawable> drawableRef = drawableMap.get(urlString); 
    if (drawableRef != null) { 
        Drawable drawable = drawableRef.get(); 
        if (drawable != null) 
            return drawable; 
        
        drawableMap.remove(urlString); 
    } 
 
    if (Constants.LOGGING) Log.d(this.getClass().getSimpleName(), "image url:" + urlString); 
    try { 
        InputStream is = fetch(urlString); 
        Drawable drawable = Drawable.createFromStream(is, "src"); 
        drawableRef = new SoftReference<Drawable>(drawable); 
        drawableMap.put(urlString, drawableRef); 
        if (Constants.LOGGING) Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", " 
                + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", " 
                + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth()); 
        return drawableRef.get(); 
    } catch (MalformedURLException e) { 
        if (Constants.LOGGING) Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e); 
        return null; 
    } catch (IOException e) { 
        if (Constants.LOGGING) Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e); 
        return null; 
    } 
} 
 
public void fetchDrawableOnThread(final String urlString, final ImageView imageView) { 
    SoftReference<Drawable> drawableRef = drawableMap.get(urlString); 
    if (drawableRef != null) { 
        Drawable drawable = drawableRef.get(); 
        if (drawable != null) { 
            imageView.setImageDrawable(drawableRef.get()); 
            return; 
        } 
        // Reference has expired so remove the key from drawableMap 
        drawableMap.remove(urlString); 
    } 
 
    final Handler handler = new Handler() { 
        @Override 
        public void handleMessage(Message message) { 
            imageView.setImageDrawable((Drawable) message.obj); 
        } 
    }; 
 
    Thread thread = new Thread() { 
        @Override 
        public void run() { 
            //TODO : set imageView to a "pending" image 
            Drawable drawable = fetchDrawable(urlString); 
            Message message = handler.obtainMessage(1, drawable); 
            handler.sendMessage(message); 
        } 
    }; 
    thread.start(); 
}