Composing Mail in SwiftUI

//
//  MailView.swift
//  sky-earth-human
//
//  Source: https://stackoverflow.com/a/58693164/9568307
//

import MessageUI
import SwiftUI
import UIKit

struct MailView: UIViewControllerRepresentable {
  @Environment(\.presentationMode) var presentation
  @Binding var result: Result<MFMailComposeResult, Error>?

  class Coordinator: NSObject, MFMailComposeViewControllerDelegate {
    @Binding var presentation: PresentationMode
    @Binding var result: Result<MFMailComposeResult, Error>?

    init(presentation: Binding<PresentationMode>,
         result: Binding<Result<MFMailComposeResult, Error>?>)
    {
      _presentation = presentation
      _result = result
    }

    func mailComposeController(_: MFMailComposeViewController,
                               didFinishWith result: MFMailComposeResult,
                               error: Error?)
    {
      defer {
        $presentation.wrappedValue.dismiss()
      }
      guard error == nil else {
        self.result = .failure(error!)
        return
      }
      self.result = .success(result)
    }
  }

  func makeCoordinator() -> Coordinator {
    return Coordinator(presentation: presentation,
                       result: $result)
  }

  func makeUIViewController(context: UIViewControllerRepresentableContext<MailView>) -> MFMailComposeViewController {
    let vc = MFMailComposeViewController()
    vc.setToRecipients(["[email protected]"])
    vc.setSubject("하늘땅사람 관련 문의")
    vc.setMessageBody("""

    문의 내용을 여기에 입력해주세요.

    --------------------

    하늘땅사람 버전: ((Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String)!)
    iOS 버전: (UIDevice.current.systemVersion)
    기기: (UIDevice.current.model)

    """, isHTML: false)
    vc.mailComposeDelegate = context.coordinator
    return vc
  }

  func updateUIViewController(_: MFMailComposeViewController,
                              context _: UIViewControllerRepresentableContext<MailView>) {}
}

Button(action: {self.isShowingMailView.toggle()}) {
  Image(systemName: "paperplane.fill").frame(alignment: .center)
  Text("버그 제보 및 기능 제안하기")
}
  .disabled(!MFMailComposeViewController.canSendMail())
  .sheet(isPresented: $isShowingMailView) {
    MailView(result: self.$result)
  }