application(_:didFinishLaunchingWithOptions:)' nearly matches optional requirement

Question

After installing Xcode 8 beta 6, I'm getting a warning saying:

Instance method 'application(_:didFinishLaunchingWithOptions:)' nearly matches optional requirement 'application(_:didFinishLaunchingWithOptions:)' of protocol 'UIApplicationDelegate'

in my App Delegate.

There are 2 suggested fixits to silence the warning:

1. Mark the method as private
2. Add @nonobjc to the method

Doing either silences the warning. But why does this need to be done?

Answer 1

iOS 12 SDK Update

In the iOS 12 SDK (that ships with Xcode 10), UIApplicationLaunchOptionsKey has now been renamed to the nested type UIApplication.LaunchOptionsKey, so you'll want:

func application(
  _ application: UIApplication,
  didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
    // ...
}

---

iOS 10 and 11 SDKs (Xcode 8 and 9)

This warning is due to the fact that the didFinishLaunchingWithOptions: parameter of the application(_:didFinishLaunchingWithOptions:) delegate method is now bridged to Swift as a [UIApplicationLaunchOptionsKey: Any]?, rather than an [NSObject : AnyObject]?.

Therefore you'll need to update your implementation to reflect this change:

func application(
  _ application: UIApplication,
  didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?
) -> Bool {
    // ...
}

Note that neither of Xcode's suggested fixes will actually fix the problem, they'll only conceal your implementation of application(_:didFinishLaunchingWithOptions:) from Objective-C – meaning that it'll never actually get called.