SwiftUI UITextView 协调器不工作

我包了一个UITextView in a UIViewRepresentable并包括一个Coordinator as UITextViewDelegate，但事件未被调用。我究竟做错了什么？

struct TextView : UIViewRepresentable {
    typealias UIViewType = UITextView

    var placeholder : String

    @Binding var text: String

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    func makeUIView(context: UIViewRepresentableContext<TextView>) -> UITextView {
        let textView = UITextView()
        let placeholderLabel = UILabel()        
        textView.font = UIFont(name: "Helvetica", size: 16)
        placeholderLabel.restorationIdentifier = "Placeholder"
        placeholderLabel.text = self.placeholder
        placeholderLabel.font = UIFont.italicSystemFont(ofSize: (textView.font?.pointSize)!)
        placeholderLabel.sizeToFit()
        textView.addSubview(placeholderLabel)
        placeholderLabel.frame.origin = CGPoint(x: 25, y: (textView.font?.pointSize)! / 2 + 12)
        placeholderLabel.textColor = UIColor.lightGray
        placeholderLabel.isHidden = !textView.text.isEmpty

        return textView
    }

    func updateUIView(_ uiView: UITextView, context: UIViewRepresentableContext<TextView>) {
        uiView.text = self.text
    }

    class Coordinator : NSObject, UITextViewDelegate {

        var parent: TextView

        init(_ uiTextView: TextView) {
            self.parent = uiTextView
        }

        func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
            print("Not working")
            return true
        }

        func textViewDidChange(_ textView: UITextView) {
            print("Not working")
        }


    }

}

这是 Xcode 版本 11.0 beta 6 中的一个工作示例：

import SwiftUI

struct ContentView: View {
     @State var text = ""

       var body: some View {
        VStack {
            Text("text is: \(text)")
            TextView(
                text: $text
            )
                .frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: .infinity)
        }

       }
}

struct TextView: UIViewRepresentable {
    @Binding var text: String

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    func makeUIView(context: Context) -> UITextView {

        let myTextView = UITextView()
        myTextView.delegate = context.coordinator

        myTextView.font = UIFont(name: "HelveticaNeue", size: 15)
        myTextView.isScrollEnabled = true
        myTextView.isEditable = true
        myTextView.isUserInteractionEnabled = true
        myTextView.backgroundColor = UIColor(white: 0.0, alpha: 0.05)

        return myTextView
    }

    func updateUIView(_ uiView: UITextView, context: Context) {
        uiView.text = text
    }

    class Coordinator : NSObject, UITextViewDelegate {

        var parent: TextView

        init(_ uiTextView: TextView) {
            self.parent = uiTextView
        }

        func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
            return true
        }

        func textViewDidChange(_ textView: UITextView) {
            print("text now: \(String(describing: textView.text!))")
            self.parent.text = textView.text
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}