how to lock portrait orientation for only main view using swift

According to the Swift Apple Docs for supportedInterfaceOrientations:

Discussion

When the user changes the device orientation, the system calls this method on the root view controller or the topmost presented view controller that fills the window. If the view controller supports the new orientation, the window and view controller are rotated to the new orientation. This method is only called if the view controller’s shouldAutorotate method returns true.

Your navigation controller should override shouldAutorotate and supportedInterfaceOrientations as shown below. I did this in a UINavigationController extension for ease:

extension UINavigationController {
    public override func shouldAutorotate() -> Bool {
        return true
    }

    public override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
        return (visibleViewController?.supportedInterfaceOrientations())!
    }
}

And your main viewcontroller (portrait at all times), should have:

override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
    return UIInterfaceOrientationMask.Portrait
}

Then, in your subviewcontrollers that you want to support portrait or landscape:

override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
    return UIInterfaceOrientationMask.All
}

Edit: Updated for iOS 9 🙂