Android异步任务下载图像错误

   private static class asyncDownloadImage extends AsyncTask<Object, Integer, Integer> 
    {
        Bitmap _image=null;

        @Override
        protected Integer doInBackground(Object... params) {

            String _url=com.nag.online.utils.objectToString(params[0]);

            byte tries=0;

            do  {
                _image          = com.nag.online.utils.downloadPicture(_url);

                try {Thread.sleep(10);} catch (InterruptedException e) {    e.printStackTrace(); }

                tries++; if (tries>utils.TRIES) break;
            } while (_image==null);

            final Bitmap _imagex=_image;

            Runnable r = new Runnable() {   
                public void run() {   
                    ImageViewImage.setImageBitmap(_imagex);
                    ImageViewImage.setScaleType(ScaleType.CENTER);
                    ImageViewImage.refreshDrawableState();
                }};

            handler.post(r);  
            isReady=true;

            return 0;
      }

        @Override
        protected void onPostExecute(Integer result) {
            /*if (!_image.isRecycled()) {
                _image.recycle();
                _image=null;
                System.gc();
            }*/

            System.gc();
        }
    }

11-10 13:32:07.057:错误/dalvikvm(4904):内存不足:堆大小=8455KB,已分配=5755KB,位图大小=7855KB

或者当我在“onpostcexecute”的代码中输入时:

 if (!_image.isRecycled()) {
                _image.recycle();
                _image=null;
                System.gc();
            }

11-10 13:40:55.117:ERROR/AndroidRuntime(4981):java.lang.RuntimeException:Canvas:尝试使用回收位图android.graphics.bitmap@44cadc98