Delegates.swift

protocol CustomSubviewDelegate: class {
    func customSubview(_ customSubview: CustomSubview, didEnterText text: String)
}

class CustomSubview: UIView {
    weak var delegate: CustomSubviewDelegate?
    
    // init and setup and stuff 
    
    @objc func textFieldDidChange(_ textField: UITextField) {
        delegate?.customSubview(self, didEnterText: textField.text!)
    }
}

class CustomViewController {
    
    func viewDidLoad() {
        customSubview.delegate = self
    }
}

extension CustomViewController: CustomSubviewDelegate {
    func customSubview(_ customSubview: CustomSubview, didEnter text: String) {
        print(text)
    }
}