// 拿到 AppDelegate

let tempAppDelegate = UIApplication .sharedApplication().delegate;

tempAppDelegate!.window!!.rootViewController = XNMainController();

// 拿到 AppDelegate
let tempAppDelegate = UIApplication .sharedApplication().delegate as! AppDelegate;

OC

// 拿到 AppDelegate AppDelegate *tempAppDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate]; XNViewController *vc = [[XNViewController alloc]init]; tempAppDelegate.window.rootViewController = vc;