我还需要设置入口点吗？ （初始视图控制器）

Question

I'm setting the rootViewController of the window programatically, like this ( didFinishLaunchingWithOptions under AppDelegate 's application method):

let storyboard = UIStoryboard(name: "Main", bundle: nil)
let rootViewController = storyboard.instantiateViewControllerWithIdentifier("loginScreen")

window = UIWindow(frame: UIScreen.mainScreen().bounds)
window?.makeKeyAndVisible()

if let window = window {
    window.rootViewController = rootViewController
}

Am I still required to go in the Interface Builder and set that controller as initial view controller? I get Failed to instantiate the default view controller for UIMainStoryboardFile 'Main' - perhaps the designated entry point is not set? If I set an entry point I have no problem and the error disappears. I want to know what is the correct way of programatically loading views. It's weird to set the rootViewController both programatically and by interface builder. Note that I am a beginner.

Answer 1

Please check the tick mark 'Is Initial View Controller' in controller properties, And then clean and run. If still exists, please try this

   UIApplication.sharedApplication().keyWindow?.rootViewController = viewController;