Getting Error while upgrading to new Xcode 12

Question

My App is using CoreLocation and CLLocationManager and is working fine in iOS 13 and iOS 12.

I have implemented new feature of Precise Location in iOS 14 using Xcode 12 and its working fine in iOS 14, iOS 13, iOS 12.

But When I execute ths Xcode 12 code in Xcode 11 version (Xcode 11.7) then I am getting error

Cannot infer contextual base in reference to member 'reducedAccuracy'

Value of type 'CLLocationManager' has no member 'accuracyAuthorization'

 if #available(iOS 14.0, *) {
        if authorizationStatus.accessLevel == .granted && locationManager.accuracyAuthorization == .reducedAccuracy {
            return .locationAlwaysAllowPreciseLocationOff
        }
        if authorizationStatus.accessLevel == .denied && locationManager.accuracyAuthorization == .fullAccuracy {
            return .locationDeniedPreciseLocationON
        }
    }


  // MARK: iOS 14 location function.
@available(iOS 14.0, *)
func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
    // iOS 14 Location Delegate method, not available in iOS 13 version
}

and here the error is

Static member 'authorizationStatus' cannot be used on instance of type 'CLLocationManager'

As i Know Precise Location is feature of iOS 14 and its not available in below versions and "accuracyAuthorization", ".reducedAccuracy", ".fullAccuracy" is not available in iOS 13 versions.

My Question is how can i make my code run in Xcode 11 versions. I have already added the isAvailable check to check the device version.

Thanks in advance :)

Answer 1

No amount of #available or @available marking is going to help you in this situation.

Why not? Well, you're doing an unexpected thing: you are opening an Xcode 12 project in Xcode 11. Your code was compiled originally in Xcode 12, where iOS 14 is a thing. So it compiled successfully. But now you open the same project in Xcode 11, where iOS 14 is not a thing. Nothing about this environment has the slightest idea that it exists. Therefore, code that involves something unique to iOS 14 will not compile. If the compiler sees that code, you are toast.

So is all hope lost? Not quite! Suppose we were to hide the code from the compiler. If we do that — if we can arrange things so that, in Xcode 11, the compiler never sees this code at all — then we will be able to compile in Xcode 11.

Well, we can do that! We can use a compilation condition. All we need is some condition that we are allowed to check against, that will distinguish what version of Xcode this is. And there is such a condition — the Swift version.

So, we can write this, for example:

class ViewController: UIViewController {
    let manager = CLLocationManager()
    override func viewDidLoad() {
        super.viewDidLoad()
        #if swift(>=5.3)
        let status = manager.authorizationStatus
        print(status.rawValue)
        #endif
    }
}

That code compiles in both Xcode 12 and Xcode 11, because in Xcode 11 the compilation condition fails, and the compiler never even looks inside the #if block.

In fact, we can provide an alternative version of the code, to be used in Xcode 11. In order to make this work as we desire, we will also have to restore your #available check, because we have to make the project's deployment target iOS 13, and the Xcode 12 compiler will complain if we don't protect the iOS 14 code:

class ViewController: UIViewController {
    let manager = CLLocationManager()
    override func viewDidLoad() {
        super.viewDidLoad()
        #if swift(>=5.3)
        if #available(iOS 14.0, *) {
            let status = manager.authorizationStatus
            print(status.rawValue)
        }
        #else
        let status = CLLocationManager.authorizationStatus()
        print(status.rawValue)
        #endif
    }
}

That code compiles and behaves correctly in either Xcode 11 or Xcode 12. Do you understand why? Let's review, because it's a bit tricky.

• In Xcode 11, the whole #if section is never seen by the compiler. It sees only this:

        let status = CLLocationManager.authorizationStatus()
        print(status.rawValue)
  

  That's good iOS 13 code, so all is well.

• In Xcode 12, the whole #else section is never seen by the compiler. It sees only this:

        if #available(iOS 14.0, *) {
            let status = manager.authorizationStatus
            print(status.rawValue)
        }
  

  That's good iOS 14 code, because, even though our project's deployment target is iOS 13, we have calmed the compiler's nerves by guaranteeing that this code won't execute in iOS 13 (where it would crash if it did execute).

Having said all that, the real answer is: don't. Everything I just did is way too much trouble! Once you've written code under Xcode 12, don't try to open that project in Xcode 11. That's not the way to test for backward compatibility.