报错---[UIApplication _runWithMainScene:transitionContext:completion:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3505.16/UIApplication.m:3294**

原因：

新的SDK不允许在设置rootViewController之前做过于复杂的操作，导致在didFinishLaunchingWithOptions 结束后还没有设置rootViewController
Xcode7需要所有UIWindow必须立即先设置一个rootViewController

解决办法:
先设置个rootVIewController 之后重新赋值

UIWindow *window = [[UIWindowalloc] initWithFrame:[UIScreenmainScreen].bounds];
window.rootViewController = [UIViewController new];