public void addImageDownloadTask(Runnable task){
  if (imageDownloadExecutor == null || imageDownloadExecutor.isShutdown()) {
    imageDownloadExecutor=createImageDownloadExecutor();
  }
  imageDownloadExecutor.execute(task);
}

public void addImageDownloadTask ( Runnable task ) { if ( imageDownloadExecutor == null || imageDownloadExecutor . isShutdown ( ) ) { imageDownloadExecutor = createImageDownloadExecutor ( ) ; } imageDownloadExecutor . execute ( task ) ; }
add a image download task to the queue
