SwiftUI UIViewRepresentable Example

example.swift

final class UIKitTextField: UITextField {}


final class Box<T> { 
  var value: T
  init(_ value: T) {
    self.value = value
  }
}

struct TextFieldProxy { 
  fileprivate var box: Box<UIKitTextField?> = Box(nil)
  
  public var isFirstResponder: Bool {
    box.value?.isFirstResponder ?? false
  }

    @discardableResult
    public func becomeFirstResponder() -> Bool {
        box.value?.becomeFirstResponder() ?? false
    }

    @discardableResult
    public func resignFirstResponder() -> Bool {
        box.value?.resignFirstResponder() ?? false
    }

    struct BoxKey: EnvironmentKey {
        static var defaultValue: Box<UIKitTextField?>? = nil
    } 
}

private extension EnvironmentValues {
    var textFieldBox: Box<UIKitTextField?>? {
        get {
            self[TextFieldProxy.BoxKey.self]
        }
        set {
            self[TextFieldProxy.BoxKey.self] = newValue
        }
    }
}




public struct TextFieldReader<Content: View>: View {
    @State private var proxy = TextFieldProxy()

    private let content: (TextFieldProxy) -> Content

    public init(@ViewBuilder content: @escaping (TextFieldProxy) -> Content) {
        self.content = content
    }

    public var body: some View {
        content(proxy)
            .environment(\.textFieldBox, proxy.box)
    }
}

public extension UIKitTextField { 
  struct SwiftUI: View { 
    var body: some View {
      UIKitTextFieldRepresentable()
    }
  }
}



struct UIKitTextFieldRepresentable: UIViewRepresentable {
   func makeUIView(context: Context) -> UIKitTextField {
     let view = UIKitTextField()
     return view
   }
  
  func updateUIView(_ uiView: UIKitTextField, context: Context) {
    if context.environment.textfieldBox.value !== uiView {
      context.environment.textfieldBox.value = uiView
    }
  }
}