点击Contact按钮触发黑屏，伴KVC报错，邮件编辑器无法显示

Let's tackle both of your problems one by one, like we're debugging together:

1. Resolve the keyPath KVC Error #

The error message this class is not key value coding-compliant for the key keyPath is a classic clue: somewhere in your Storyboard/XIB, your Contact button has a User Defined Runtime Attribute set for a key named keyPath, but your code doesn't define this property.

Here's how to fix it:

• Open your Storyboard/XIB file
• Select the Contact button that triggers the email action
• Switch to the Identity Inspector (third tab on the right sidebar)
• Scroll down to User Defined Runtime Attributes
• Look for any entry with keyPath as the Key — delete that entry completely

This will stop the error from popping up when you use the SWReveal slide menu.

2. Fix the Black Screen When Tapping "Contact" #

The root cause of the black screen is a wrong inheritance choice: your SendEmailVC is subclassing MFMailComposeViewController, but you shouldn't inherit from this controller. Instead, you should create an instance of it and present it normally.

Here's the fix:

• Change your class inheritance from MFMailComposeViewController to UIViewController
• Remove the unused contact() call in your Send_Tapped method (it's not defined anywhere, so it's just dead code)

Modified Working Code #

import Foundation
import UIKit
import MessageUI

class SendEmailVC: UIViewController, MFMailComposeViewControllerDelegate {
    @IBAction func Send_Tapped(_ sender: Any) {
        if MFMailComposeViewController.canSendMail() {
            let mailComposeViewController = configureMailController()
            self.present(mailComposeViewController, animated: true, completion: nil)
        } else {
            showMailError()
        }
    }
    
    func configureMailController() -> MFMailComposeViewController {
        let mailComposerVC = MFMailComposeViewController()
        mailComposerVC.mailComposeDelegate = self
        mailComposerVC.setToRecipients(["testing@gmail.com"])
        mailComposerVC.setSubject("Hello")
        mailComposerVC.setMessageBody("How are you doing?", isHTML: false)
        return mailComposerVC
    }
    
    /*
     * DON'T EDIT THE CODE BELOW.
     */
    func showMailError() {
        let sendMailErrorAlert = UIAlertController(title: "Email failed to send", message: "Your device fail to send the email", preferredStyle: .alert)
        let dismiss = UIAlertAction(title: "Dale", style: .default, handler: nil)
        sendMailErrorAlert.addAction(dismiss)
        self.present(sendMailErrorAlert, animated: true, completion: nil)
    }
    
    func mailComposeController(_ controller: MFMailComposeViewController, didFinishWith result: MFMailComposeResult, error: Error?) {
        controller.dismiss(animated: true, completion: nil)
    }
}

Quick Extra Check #

Double-check that your SendEmailVC is properly linked in the Storyboard: make sure the view controller's class is set correctly in the Identity Inspector, and the Send_Tapped action is connected to your Contact button.

内容的提问来源于stack exchange，提问作者Palermox