我收到错误“类型'（UITextRange）->字符串？' 不能符合“BinaryInteger”； 只有结构/枚举/类类型可以符合协议”

Question

I'm new to Swift Programming and I made a simple project which will give output to a label, but I'm getting the error:

Type '(UITextRange) -> String?' cannot conform to 'BinaryInteger'; only struct/enum/class types can conform to protocol.

Can anyone explain what's happening?

@IBOutlet weak var lblOutput: UILabel!
@IBOutlet weak var InputAge: UITextField!

@IBOutlet weak var outputAge: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
}

@IBAction func calcOutput(_ sender: Any) {
    var age = Int(InputAge.text) * 8;
    lblOutput.text = age;
}

Image containing the error:

Answer 1

There are three mistakes:

1. You have to unwrap text of inputAge , this can be forced because the text property of UITextField is never nil
2. For example "ABC" cannot be converted to Int , therefore Int(...) returns an optional and you have to check if it's nil
3. The type of the text property of UILabel is String . You have to convert the result of the multiplication back to String

And please name functions and variables with starting lowercase letter and declare immutable variables as constants ( let )

    @IBOutlet weak var inputAge : UITextField!
    
    @IBAction func calcOutput(_ sender: Any) {
        let stringAge = inputAge.text! 
        if let age = Int(stringAge) {
            lblOutput.text = String(age * 8)
        } else {
            lblOutput.text = "The input string is not convertible to Int"
        }
    }

Answer 2

Unwrap optional of text before use:

@IBAction func calcOutput(_ sender: Any) {
    if let text = validatedField.text,
       let age = Int(text) {
        lblOutput.text = "\(age * 8)"
    }
}

Don't use semicolons at the lines end.

Use let if you don't update its values later.

Set text to text fields (not Int).