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在加载所有列表项期间，我尝试在后台加载缩略图。我得到一个错误和程序崩溃。我不知道是什么问题。

（1）我得到列表项ID

  String id = listIDs.get(position);
  task.execute(id);

(2)加载缩略图的AsyncTack如下

        //Lazy image update
        class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
        private final WeakReference<ImageView> imageViewReference;  
        public BitmapWorkerTask(ImageView imageView) {
            // Use a WeakReference to ensure the ImageView can be garbage collected
            imageViewReference = new WeakReference<ImageView>(imageView);
        }

        // Decode image in background.
        @Override
        protected Bitmap doInBackground(String... params) {
            Bitmap bitmap = null;
            dbHelper.open();
            byte[] img_bytes = dbHelper.getImagebyIDnumber(params[0]);          
            bitmap = BitmapFactory.decodeByteArray(img_bytes, 0, img_bytes.length);        
            dbHelper.close();        
            return bitmap;
        }

        // Once complete, see if ImageView is still around and set bitmap.
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (imageViewReference != null && bitmap != null) {
                final ImageView imageView = imageViewReference.get();
                if (imageView != null) {
                    imageView.setImageBitmap(bitmap);
                }
            }
        }   


    }

(3)数据库中获取byte[]图像数据的事件

      public byte[] getImagebyIDnumber(String idnum){
         Cursor mCursor = null;
         mCursor = mDb.query(SQLITE_TABLE, new String[] {KEY_ROWID,
                   KEY_IDNUM, KEY_SIMCARD, KEY_DESCRIPTION, KEY_MODEL, KEY_TIMEINSTANCE, KEY_PASSWORD,
                   KEY_LOCATIONAUTOUPDATE, KEY_OVERSPEED, KEY_MOVEMENT, KEY_GEOFENCE, KEY_TIMEZONE, KEY_AUTHORIZE, KEY_IMAGE, KEY_ACTIVATE, KEY_NUMOFUSE}, 
                   KEY_IDNUM + " like '%" + idnum + "%'", null, null, null, null, null);
         byte[] img_bytes = mCursor.getBlob(13);
         return img_bytes;
     }

错误发生在后台循环中。我的红色logcat是

08-19 22:45:05.690: D/dalvikvm(29110): threadid=17: still suspended after undo (sc=1 dc=1)
08-19 22:45:05.690: D/dalvikvm(29110): threadid=18: still suspended after undo (sc=1 dc=1)
08-19 22:45:05.705: E/AndroidRuntime(29110): FATAL EXCEPTION: AsyncTask #2
08-19 22:45:05.705: E/AndroidRuntime(29110): java.lang.RuntimeException: An error occured while executing doInBackground()
08-19 22:45:05.705: E/AndroidRuntime(29110):    at android.os.AsyncTask$3.done(AsyncTask.java:299)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
08-19 22:45:05.705: E/AndroidRuntime(29110):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
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