高效率下载图片——防止内存溢出(2)

    //下载队列 
    private List<ImageDownloadItem> queue = new ArrayList<ImageDownloadItem>(); 
    private synchronized void addDownloadItem(ImageDownloadItem item) { 
        queue.add(item); 
        this.notify();//添加了下载项就激活本线程 
    } 
 
    @Override 
    public void run() { 
        while(true) { 
            while(queue.size() > 0) { 
                ImageDownloadItem item = queue.remove(0); 
                String imagePath = downloadImage(item.imageUrl); 
                //缓存图片路径 
                cache.put(item.imageUrl, imagePath); 
 
                if (item.callback != null) {//需要执行回调来显示图片 
                    item.imagePath = imagePath; 
 
                    //交由UI线程处理 
                    Message msg = handler.obtainMessage(); 
                    msg.obj = item; 
                    handler.sendMessage(msg); 
                } 
            } 
            try { 
                synchronized(this) { 
                    this.wait();//没有下载项时等待 
                } 
            } catch (InterruptedException e) { 
                e.printStackTrace();