iOS --- Swift -Storyboard 更改根视图

当项目中用storyboard开发到时候，避免不了更改根视图， 比如第一次打开APP的时候， 就会显示不同的根视图。

话不多说直接开撸
Swift 3
1.当 storyboard根控制器为UITabBarController的时候,在storyboard中设置根视图identifier

   let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
    let viewController = mainStoryboard.instantiateViewController(withIdentifier: "tabBarcontroller") as! UITabBarController
    UIApplication.shared.keyWindow?.rootViewController = viewController

2. 当storyboard根控制器为UINavigationController的时候

    let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
    let viewController = mainStoryboard.instantiateViewController(withIdentifier: "FirstView") as! UINavigationController
   UIApplication.shared.keyWindow?.rootViewController = viewController
   

OC

 UIStoryboard *storyboard = [UIStoryboard     storyboardWithName:@"MainStoryboard" bundle:nil];
UITabBarController *rootViewController = [storyboard instantiateViewControllerWithIdentifier:@"tabBarcontroller"];
[[UIApplication sharedApplication].keyWindow setRootViewController:rootViewController];