二进制运算符“ +”不能应用于类型为“字符串”和“字符串感叹号”的操作数

Question

I am generating a QRCode with name, email and phone number of user which are entered in registration form. In RegistrationVC, I have used userdefaults to save all these 3 fields. Now in my QRGenerate VC, with the help of user default I want to generate QR code, but throwing an error

Binary operator '+' cannot be applied to operands of type 'String' and 'String!".

I am passing all three keys to a string (ieqrgeneratestring) and generating QRCodes.

phoneKeyValue = UserDefaults.standard.string(forKey: "phoneKey")
nameKeyValue = UserDefaults.standard.string(forKey: "nameKey")
emailidKeyValue = UserDefaults.standard.string(forKey: "emailIDKey")
var qrgeneratestring = nameKeyValue + emailidKeyValue + phoneKeyValue


    if qrgeneratestring.isEmpty == false{
        let ciImageFromQRCode = generateQRCodeFromString(strQR: qrgeneratestring)
        let scaleX = (imgViewQRCode.frame.size.width / ciImageFromQRCode.extent.size.width)
        let scaleY = (imgViewQRCode.frame.size.height / ciImageFromQRCode.extent.size.height)
        let imgTransformed = ciImageFromQRCode.applying(CGAffineTransform(scaleX: scaleX, y: scaleY))
        imgViewQRCode.image = UIImage(ciImage: imgTransformed)

    }

Answer 1

string(forKey returns an optional, you need to unwrap the three values and you have to declare the variables as non-optional

var phoneKeyValue = ""
var nameKeyValue = ""
var emailidKeyValue = ""

let defaults = UserDefaults.standard
phoneKeyValue = defaults.string(forKey: "phoneKey") ?? ""
nameKeyValue = defaults.string(forKey: "nameKey") ?? ""
emailidKeyValue = defaults.string(forKey: "emailIDKey") ?? ""

Answer 2

The UserDefaults method string(forKey:...) returns an optional - that is a value that can either be of the type String, or nil.

You need to unwrap the optional, either using exclamation mark ! or using the coalesence operator ?? . This depends on whether you know the value can't be nil (so you use exclamation mark) or you provide a default value when the optional is a nil value.

In this case I would use:

phoneKeyValue = UserDefaults.standard.string(forKey: "phoneKey") ?? ""
nameKeyValue = UserDefaults.standard.string(forKey: "nameKey") ?? ""
emailidKeyValue = UserDefaults.standard.string(forKey: "emailIDKey") ?? ""
var qrgeneratestring = nameKeyValue + emailidKeyValue + phoneKeyValue