완성 이미지

코드

import SwiftUI

struct ContentView: View {
    @State var text = "default text"
    var body: some View {
        VStack {
            MultiTextView(text: $text)
            Text(text)
                .frame(maxWidth: .infinity, maxHeight: .infinity)
        }
    }
}

struct MultiTextView: NSViewRepresentable {
    @Binding var text: String

    func makeNSView(context: Context) -> NSTextView {
        let view = NSTextView()
        view.delegate = context.coordinator
        view.string = text
        return view
    }

    func updateNSView(_ nsView: NSTextView, context: Context) {
        // この行はいらなかった。
        nsView.string = text
    }

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

    class Coordinator: NSObject, NSTextViewDelegate {
        var multiTextView: MultiTextView
        init(_ multiTextView: MultiTextView) {
            self.multiTextView = multiTextView
        }
        func textDidChange(_ notification: Notification) {
            guard let text = notification.object as? NSText else {
                return
            }
            self.multiTextView.text = text.string
        }
    }
}