首先先看看這個 extension

extension UITextField {
    var textPublisher: AnyPublisher<String?, Never> {
        NotificationCenter.default // 1
            .publisher(for: UITextField.textDidChangeNotification, object: self)
            .compactMap { $0.object as? UITextField } // 2
            .filter { $0 == self } // 3
            .map { $0.text}
            .eraseToAnyPublisher()
    }
}

1. 我們建立一個來自 NotificationCenter的 Publisher
2. 從通知提取 Object 並轉型
3. 確認發佈來源

透過這樣的方式, 我們可以創造 UITextField 的事件流!

import Combine


class ViewController: UIViewController {
    @IBOutlet  var aTextFileld: UITextField!
    @IBOutlet  var bTestField: UITextField!
    var set = Set<AnyCancellable>()
    
    let vc = UIViewController()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        aTextFileld.textPublisher
            .assign(to: \UITextField.text, on: bTestField)
        .store(in: &set)
    }

}

如此, 就可以利用 UIKit 來理解 Combine 了

簡單測驗:

1. 試試看套用所有的 UICotrol

參考來源: Multiple UITextFields and textDidChangeNotification notification
https://stackoverflow.com/a/56796398/10172299