我不能使用委托和协议来传递数据

Question

我学习 Swift，我想使用委托和协议将 Json api 数据传递给 viewController：

在viewController中：

  class exchangeViewController: UIViewController { 

var exchange = Exchange(baseUri: "http://data.fixer.io/api/latest?access_key=", apiKey: "apiKey")
@IBOutlet weak var inputEuro: UITextField!
@IBOutlet weak var getDollar: UILabel!
override func viewDidLoad() {
    super.viewDidLoad()
    
    exchange.delegate? = self
}

@IBAction func exchangeCurrency(_ sender: UIButton) {
    print("button1")
    exchange.fitchData()
    print("button2")
} }


extension exchangeViewController: ExchangeCurrencyDelegate {
func didRetriveDollarvalue(dollar: Dollar) {
  
        print(dollar.base + " e1")
        self.getDollar.text = dollar.base
        print(dollar.base + " e2")
      }       
   }

型号 Class:

protocol ExchangeCurrencyDelegate{
func didRetriveDollarvalue(dollar: Dollar)    }

class Exchange{
var delegate : ExchangeCurrencyDelegate?
var baseUri : String
var apiKey  : String

init(baseUri: String, apiKey: String){
    self.baseUri = baseUri
    self.apiKey = apiKey
}
func fitchData(){
    
    let url = URL(string: baseUri + apiKey)
    
    let session = URLSession(configuration: .default)
    
    let task = session.dataTask(with: url!, completionHandler: taskHandler(data:urlresponse:error:))
    
    task.resume()
}

func taskHandler(data: Data?, urlresponse: URLResponse?, error: Error?) -> Void{
    do {
        
        let dollarValue:Dollar = try JSONDecoder().decode(Dollar.self, from: data!)
       
            print(dollarValue.base + " a")
            delegate?.didRetriveDollarvalue(dollar: dollarValue)
            print(dollarValue.base + " b")
     
        
    }
    catch {
        print(error)
    }
}  }

美元结构：

struct Dollar: Decodable{
var base: String }

当我执行这个应用程序时，我可以打印：按钮1，按钮2， dollarValue.base + "一个", dollarValue.base + "b", 但我无法在扩展 exchangeViewController.

中执行 didRetriveDollar 协议

当我使用断点时，程序超出了模型 class 中的 delegate?.didRetriveDollarvalue(dollar: dollarValue)。谁能找到我的错在哪里？谢谢如果我的英语水平不够好，我很抱歉。

Answer 1

您似乎没有在 viewDidLoad 方法中正确设置 Exchange 委托：

exchange.delegate? = self

尝试将其更改为：

exchange.delegate = self

我不能使用委托和协议来传递数据

I can't use Delegate and Protocol to pass data

xcode

ios

swift