模擬器 從一個viewController跳轉到另一個viewController后黑屏，方法是：
1. 在storyboard里給跳轉的viewController加上StoryboardID:
image.png
2.代碼如下修改
let controller = self.storyboard?.instantiateViewController(withIdentifier: String(describing: type(of: ViewController2())))
as! ViewController2
self.navigationController?.pushViewController(controller, animated: true)
