Ambiguous reference to member 'first(where:)' error when referencing child view controller

Question

I am writing an iOS application and have a child view controller that I am trying to reference. The child view controller is the delegate of the parent.

At the top of the parent view controller, I have: fileprivate var cameraViewController: CameraViewController<AnyObject>?

In viewDidLoad(), I have

guard let cameraController = childViewControllers.first as? CameraViewController else  {
            fatalError("Check storyboard for missing CameraViewController")
        }

        cameraViewController = cameraController

However, I'm getting the error: Ambiguous reference to member 'first(where:)'

Can anyone explain to me why this is happening? I only have one child view controller for the parent.

@rmaddy then shouldn't he be referencing it as `self.childViewControllers` (assuming the code is in a UIViewController subclass)? — Michael Dautermann, Jun 04 '18 at 23:23
@MichaelDautermann `self` is optional in many cases in Swift. — rmaddy, Jun 04 '18 at 23:24
I suspect this might be one of those cases where the compiler gets lost inside a conditional unwrap. If you put `childViewControllers.first` in parentheses, does it work? — John Montgomery, Jun 04 '18 at 23:25
Cannot replicate the error. Clean and Build your project; see if that fixes it. — staticVoidMan, Jun 05 '18 at 09:18
Thanks everyone and sorry for the ambiguity of my question. I left out the detail that I was trying to make the CameraViewController the delegate of its parent. I edited the question and added the answer that fixed it. — jordan, Jun 05 '18 at 15:58

score 0 · Answer 1 · answered Jun 05 '18 at 01:49

Can't reproduce. This is the entire code in my app's single view controller file:

import UIKit
class CameraViewController : UIViewController {}
class ViewController: UIViewController {
    fileprivate var cameraViewController: CameraViewController?
    override func viewDidLoad() {
        super.viewDidLoad()
        guard let cameraController = childViewControllers.first as? CameraViewController else  {
            fatalError("Check storyboard for missing CameraViewController")
        }
        cameraViewController = cameraController
    }
}

It compiles just fine.

score 0 · Accepted Answer · answered Jun 05 '18 at 15:57

CameraViewController needs to be the same everywhere. When I instantiated cameraViewController as a CameraViewController, that needed to be reflected in the second part of the code. The second part should look like this:

guard let cameraController = childViewControllers.first as? CameraViewController<AnyObject> else  {
            fatalError("Check storyboard for missing CameraViewController")
        }

        cameraViewController = cameraController

Ambiguous reference to member 'first(where:)' error when referencing child view controller

2 Answers2