Access container view child properties swift

Question

What I want to achieve:

User presses the button in the ViewController then, the color of the button placed in the container view should change its color to red.

Answer 1

Swift 3 for macOS:

// MARK: - Container View Controller

var containerViewController: ContainerViewController?

let containerSegueIdentifier = "Container Segue"

override func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    if segue.identifier == containerSegueIdentifier {
        if let connectContainerViewController = segue.destinationController as? FormationViewController {
            formationViewController = connectContainerViewController
        }
    }
}

Check identifier and controller class.