Assertion failure in -[UIApplication _runWithMainScene:transitionContext:completion:], /BuildRoot/Li

Assertion failure in -[UIApplication _runWithMainScene:transitionContext:completion:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3512.30.14/UIApplication.m:3315

尝试解决方案二：  　　Xcode7 需要所有的窗口都必须有根控制器   XCODE 7 requires that all the Windows must have a rootViewController You can use easy:  

UIViewController* vc = [[UIViewController alloc]initWithNibName:nil bundle:nil];  self.window.rootViewController = vc; 

  It's working good if you need to use only UIWindow (for easy examples from any Tutorials - before Xcode 7)!