当你需要更新UI并在viewDidLoad中调用时，你如何处理Parse调用主线程？

I'm really struggling with the multi-threading concept. All calls to Parse are done off the main thread which I understand is because you don't want to block the main thread while waiting for a reply. But what do I do if I need to get data from parse to update my UI before the screen is displayed?I'm really struggling with the multi-threading