xcode 无法将“()”类型的值转换为预期的参数类型“String”

Cannot convert value of type '()' to expected argument type 'String'

提问by hg56

I am taking the zip code entered by my user and converting it into a City name. After it is converted to the City name I will save the information into my Firebase Database. I am getting an error "Cannot convert value of type '()' to expected argument type 'String'" when I try to do this. I am getting the zip code from a text field and passing it from the previous ViewController. error

我正在获取用户输入的邮政编码并将其转换为城市名称。将其转换为城市名称后，我会将信息保存到我的 Firebase 数据库中。当我尝试执行此操作时，出现错误“无法将类型 '()' 的值转换为预期的参数类型 'String'”。我从文本字段中获取邮政编码并从前一个 ViewController 传递它。 错误

 //first ViewController


 override func prepare(for segue: UIStoryboardSegue, sender: Any?)
{


    if let destination = segue.destination as? SignUpSecondViewController{

    destination.zipCode = zipCodeInput.text! 
    destination.name = nameText.text!
    destination.email = emailText.text!
    destination.password = passwordText.text!
    destination.pictureData = userImageView.image!
    }}

}

   //second ViewController

    var zipCode = String()

 func getLocationFromPostalCode(postalCode : String){
    let geocoder = CLGeocoder()

    geocoder.geocodeAddressString(postalCode) {
        (placemarks, error) -> Void in
        // Placemarks is an optional array of type CLPlacemarks, first item in array is best guess of Address

        if let placemark = placemarks?[0] {

            if placemark.postalCode == postalCode{
                // you can get all the details of place here
                print("\(placemark.locality)")
                print("\(placemark.country)")
            }
            else{
                print("Please enter valid zipcode")
            }
        }
    }
}




 @IBAction func completeButtonAction(_ sender: Any) {

let nameText = name
let emailField = email.lowercased()
let finalEmail = emailField.trimmingCharacters(in: .whitespacesAndNewlines)
let location = getLocationFromPostalCode(postalCode: zipCode)
let biography = bioTextView.text!
let passwordText = password
let interests = options.joined(separator: " , ")

    var pictureD: NSData?


    if let imageView = self.sentPic.image {
        pictureD = UIImageJPEGRepresentation(self.sentPic.image!, 0.70) as! NSData
    }


    if  finalEmail.isEmpty || biography.isEmpty || password.isEmpty || pictureD == nil {
        self.view.endEditing(true)
        let alertController = UIAlertController(title: "OOPS", message: " You must fill all the fields", preferredStyle: .alert)
        alertController.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
        present(alertController, animated: true, completion: nil)

    }else {
        SVProgressHUD.show()

        self.view.endEditing(true)
        authService.signUP(firstLastName: nameText, email: finalEmail, location: location, biography: biography, password: password, interests: interests, pictureData: pictureD as NSData!)

    }
    SVProgressHUD.dismiss()


    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let vc = storyboard.instantiateViewController(withIdentifier: "NewTabBarViewController") as! UIViewController
    // Alternative way to present the new view controller
     self.navigationController?.present(vc, animated: true, completion: nil)


}

采纳答案by rmaddy

Your problem begins with this line:

你的问题从这一行开始：

let location = getLocationFromPostalCode(postalCode: zipCode)

The problem is that your getLocationFromPostalCodehas no return value so the compiler thinks that the implicit type of locationis ()which means a function with no return (void) type.

问题是你getLocationFromPostalCode没有返回值所以编译器认为隐式类型locationis()这意味着一个没有返回（void）类型的函数。

So, in theory, you would want to change:

所以，理论上，你会想要改变：

func getLocationFromPostalCode(postalCode : String) {

to:

到：

func getLocationFromPostalCode(postalCode : String) -> String {

and have the function return a Stringvalue.

并让函数返回一个String值。

But, you can't do that either since the implementation of your getLocationFromPostalCodeconsists of getting the location from an asynchronous network call.

但是，您也不能这样做，因为您的实现getLocationFromPostalCode包括从异步网络调用中获取位置。

The proper solution is to rewrite that function to take a completion handler that returns the obtained location.

正确的解决方案是重写该函数以获取返回获取位置的完成处理程序。

func getLocationFromPostalCode(postalCode: String, completion: (String?) -> Void) {
    let geocoder = CLGeocoder()

    geocoder.geocodeAddressString(postalCode) { (placemarks, error) -> Void in
        // Placemarks is an optional array of type CLPlacemarks, first item in array is best guess of Address

        if let placemark = placemarks?.first {
            if placemark.postalCode == postalCode {
                // you can get all the details of place here
                print("\(placemark.locality)")
                print("\(placemark.country)")
                completion(placemark.locality) // or whatever value you want
                return
            }
            else{
                print("Please enter valid zipcode")
            }
        }

        completion(nil) // no location found
    }
}

Now, with that all fixed up, you need to redo how you get the location.

现在，所有这些都解决了，您需要重做获取位置的方式。

@IBAction func completeButtonAction(_ sender: Any) {
    var pictureD: Data? = nil
    if let imageView = self.sentPic.image {
        pictureD = UIImageJPEGRepresentation(imageView, 0.70)
    }

    let emailField = email.lowercased()
    let finalEmail = emailField.trimmingCharacters(in: .whitespacesAndNewlines)
    let biography = bioTextView.text!
    let passwordText = password

    if  finalEmail.isEmpty || biography.isEmpty || password.isEmpty || pictureD == nil {
        self.view.endEditing(true)
        let alertController = UIAlertController(title: "OOPS", message: " You must fill all the fields", preferredStyle: .alert)
        alertController.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
        present(alertController, animated: true, completion: nil)
    }else {
        getLocationFromPostalCode(postalCode: zipCode) { (location) in
            guard let location = location else {
                print("no location")
                return
            }

            let nameText = name
            let interests = options.joined(separator: " , ")

            SVProgressHUD.show()

            self.view.endEditing(true)
            authService.signUP(firstLastName: nameText, email: finalEmail, location: location, biography: biography, password: password, interests: interests, pictureData: pictureD!)
            SVProgressHUD.dismiss()
        }
    }

    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let vc = storyboard.instantiateViewController(withIdentifier: "NewTabBarViewController") as! UIViewController
    // Alternative way to present the new view controller
    self.navigationController?.present(vc, animated: true, completion: nil)
}