1.定义好的xib文件rootView.xib，选中files·owners  在class中选择对应的viewController

2.如何在window中指定rootViewController

------在appdelegate.h中声明属性

　@property （strong，nonatomic）rootViewController* rvc;

------在appdelegate.m中的didFinishLauchingWithOptions：方法中加载rvc

self.rvc = [[rootViewController alloc]initWithNibName:@"rootView" bundle:nil]; //rootView是rootView.xib文件的名字

self.window.rootViewController = rvc;

//显示window

[self.window makeKeyAndVisible]; 
return YES;