[Solved] Share Data Between View Controller and Container View

Question

You are on the right track to setup the delegate.

In Storyboard:

create a Segue of type Embed Segue from the ContainerView to the ViewController to embed.
Select the segue and set a Identifier.

In Code, in prepareForSegue():

Set the myContainerView propert

Set the delegate

class ViewController: UITableViewController, ContainerViewDelegate {
    var myContainerView:ContainerView? // we do initialize it in prepareForSegue()
    var id: String!

    override func viewDidLoad() {
        super.viewDidLoad()
        id = "123"
        // myContainerView.delegate = self //myContainerView is nil here. We set it in prepareForSegue
    }

    func initialize() -> String {
        return id
    }

    let embedSegueID = "the identifier you set to your embed segue in Storyboard"

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == embedSegueID) {
            let dvc = segue.destination as! ContainerView
            // Now you have a pointer to EmbeddedViewController.
            // You can save the reference to it, or pass data to it.
            myContainerView = dvc
            myContainerView.delegate = self
        }
        print(segue.identifier)
    }
}

If you want to pass data from your ViewController to AnotherViewController which is embedded in your destinationViewController (how I understand your question), I would:

pass it to destinationViewController as in the example above (prepareForSegue)
than pass it to AnotherViewController in viewWillAppear() from within destinationViewController.

In this case, how I understand your usecase, you do not need the delegate and can remove all delegate related code (initialize, the ContainerViewDelegate protocol, the property var delegate: ContainerViewDelegate! and all calls to it.

Accepted Answer