ios - 收到错误没有'+'候选者产生预期的上下文结果类型'NSString'

Question

我正在用Swift 3和Xcode 8编写代码。

这是代码:

import Foundation
import UIKit

class CashTextFieldDelegate : NSObject, UITextFieldDelegate {

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {


    let oldText = textField.text! as NSString

    var newText = oldText.replacingCharacters(in: range, with: string) as NSString

    var newTextString = String(newText)

    let digits = NSCharacterSet.decimalDigits
    var digitText = ""
    for c in newTextString.unicodeScalars {
        if digits.contains(c) {
            digitText.append(String(c))
        }
    }

    // Format the new string
    if let numOfPennies = Int(digitText) {
        newText = "$" + self.dollarStringFromInt(numOfPennies)+ "." + self.centsStringFromInt(numOfPennies)

    } else {
        newText = "$0.00"
    }

    textField.text = newText as String

    return false
}

func textFieldDidBeginEditing(_ textField: UITextField) {
    if textField.text!.isEmpty {
        textField.text = "$0.00"
    }
}

func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    textField.resignFirstResponder()

    return true;
}

func dollarStringFromInt(value: Int) -> String {
    return String(value / 100)
}

func centsStringFromInt(value: Int) -> String {

    let cents = value % 100
    var centsString = String(cents)

    if cents < 10 {
        centsString = "0" + centsString
    }

    return centsString
}

}

对于上面的这一行代码:

newText = "$" + self.dollarStringFromInt(numOfPennies) + "." + self.centsStringFromInt(numOfPennies)

我收到这样的错误:

No '+' candidates produce the expected contextual result type 'NSString'.

无法解决此错误。

没有任何解释的任何帮助将不胜感激

Answer 1

与Swift 2不同，NSString和String不会自动在彼此之间转换。

尝试这样的事情:

newText = ("$" + self.dollarStringFromInt(numOfPennies) + "." + self.centsStringFromInt(numOfPennies)) as NSString

您可以使用一致的类型来进一步清理-整个过程中使用 String或 NSString(例如，更改函数的返回值等)。