无法分配类型的值＆＃x27; viewController＆＃x27;要键入AddContactDelegate？＆＃x27;

Question

import UIKit

struct Contact  {
    var fullname: String
    var contactNumber: String
}

class ViewController: UITableViewController {

    var contacts = [Contact]()
    @IBOutlet var tableview: UITableView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
    
    @IBAction func handleAdd(_ sender: Any) {
        let controller = AddContacts()
        controller.delegate = self
        self.present(UINavigationController(rootViewController: controller), animated: true, completion: nil)
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableview.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        cell.textLabel?.text = contacts[indexPath.row].fullname
        cell.detailTextLabel?.text = contacts[indexPath.row].contactNumber
        return cell

    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return contacts.count
    }
}


import UIKit

protocol AddContactDelegate {
    func addContact(contact: Contact)
}

class AddContacts: UIViewController {

    var delegate: AddContactDelegate?
    
    @IBOutlet weak var ContactTextField: UITextField!
    @IBOutlet weak var nameTextField: UITextField!
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    
    @IBAction func save(_ sender: Any) {
        guard let fullname = nameTextField.text, nameTextField.hasText else {
            print("handle error here")
            return
        }
        
        guard let contactNumber = ContactTextField.text , ContactTextField.hasText else {
            print("enter contact error here")
            return
        }
        let contact  = Contact(fullname: fullname, contactNumber: contactNumber)
        print(contact.fullname)
        print(contact.contactNumber)
        delegate?.addContact(contact: contact)
    }
    
}

在viewController：uitaiteViewController文件中显示错误，例如无法将“ viewController”类型的值分配给type“ AddContactdelegate？”我该怎么办来解决这些错误

Answer 1

import UIKit

struct Contact  {
    var fullname: String
    var contactNumber: String
}

class ViewController: UITableViewController {

    var contacts = [Contact]()
    @IBOutlet var tableview: UITableView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
    
    @IBAction func handleAdd(_ sender: Any) {
        let controller = AddContacts()
        controller.delegate = self
        self.present(UINavigationController(rootViewController: controller), animated: true, completion: nil)
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableview.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        cell.textLabel?.text = contacts[indexPath.row].fullname
        cell.detailTextLabel?.text = contacts[indexPath.row].contactNumber
        return cell

    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return contacts.count
    }
}

//添加此

extension ViewController: AddContactDelegate {
      func addContact(contact: Contact) {
           contacts.append(contact)
           tableView.reloadData()
       }
}

//就是这样

import UIKit

protocol AddContactDelegate:AnyObject {
    func addContact(contact: Contact)
}

class AddContacts: UIViewController {

    weak var delegate: AddContactDelegate?
    
    @IBOutlet weak var ContactTextField: UITextField!
    @IBOutlet weak var nameTextField: UITextField!
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    
    @IBAction func save(_ sender: Any) {
        guard let fullname = nameTextField.text, nameTextField.hasText else {
            print("handle error here")
            return
        }
        
        guard let contactNumber = ContactTextField.text , ContactTextField.hasText else {
            print("enter contact error here")
            return
        }
        let contact  = Contact(fullname: fullname, contactNumber: contactNumber)
        print(contact.fullname)
        print(contact.contactNumber)
        delegate?.addContact(contact: contact)
    }
    
}

Answer 2

您必须在ViewController内实现协议。

为什么Xcode向您显示错误是：

protocol ViewDelegate: AnyObject {
   func didDoSomething()
}

// Which means - reference with name delegate can store objects that conform to the protocol ViewDelegate
var delegate: ViewDelegate

如果您不符合您试图将此参考存储到所需协议存储到此引用的对象，则您将无法将该对象存储到该引用中。

您可以查看像合同之类的协议，如果在特定类中实现了协议，则类必须在协议中实现声明的方法。

只需将此协议实现到您的ViewController并添加协议（合同）中声明的方法就会使您实现所需的目标。

class MyViewController: ViewDelegate {
   func didDoSomething() {
       //TODO: Logic for this method
   }
}

//Will not give compile errors
let delegate: ViewDelegate = MyViewController()

仅需提供其他信息，您就可以随时以这种方式实施一名代表，

class MyViewController {
//properties
}

//MARK: - ViewDelegate implementation
extension MyViewController: ViewDelegate {
   func didDoSomething() {
      //TODO: logic
   }
}

希望它能有所帮助。