最新的Xcode 7.2更新后应用程序启动时出现黑屏

i am making a very complicated app with a lot of classes. my app worked great and i worked on it for the last month. the last time i worked on it i added a function and it worked great, i saved the app and ran it a few times since and it worked. the last time i turned my computer on, it prompted me that an update for xcode is available. i updated it, and since then every time i run my app it runs with no errors but on ios simulator it shows a black screen. what can i do? i worked really hard on that app. thanks for the help in advance.i am making a very complicated app with a lot o