Trying to convert a hexadecimal text to a decimal in swift, but getting "Optional([num])" output

Question

I am trying to convert a hexadecimal number to a decimal number. The user inputs a hexadecimal in a textview, on text edit action the decimal textview outputs the conversion. I am getting a strange behavior where the decimal textview is displaying "Optional[num]" IE "Optional(9) if I type in 9. Here is the hexadecimal text action listener:

@IBAction func inputHex(sender: AnyObject) {
        if(Int(hexText.text!) != nil){
            inputNumberText = hexText.text!

            let st3 = Int(inputNumberText, radix: 16)
            decText.text = String(st3)
        }
    }

score 3 · Accepted Answer · edited May 23 '17 at 11:44

let st3 = Int(inputNumberText, radix: 16)

calls the "failable initializer"

init?(_ text: String, radix radix: Int = default)

of struct Int, and that is failable for a good reason: It returns nil if the string is not a valid number representation in the given base. For example

Int("12XYZ", radix: 16)
Int("789", radix: 8)

would return nil. So st3 is an optional, and therefore String(st3) is the string "Optional(...)".

But note that there are more issues with your code:

Don't use AnyObject parameters in action methods. Always use the real type (in this case: UITextField) for better type checking. Xcode has an option for that when you connect the action.
Never unwrap forcefully. Use optional binding instead.
Comparing against nil can and should be avoided in almost all cases.

With regard to the last two points, compare When should I compare an optional value to nil?.

In your case

if (Int(hexText.text!) != nil)

is even wrong because it rejects valid hexadecimal strings like "ABCD".

This is how your action method could look like:

@IBAction func inputHex(sender: UITextField) {
    if let text = sender.text,
        let number = Int(text, radix: 16) {
        decText.text = String(number)
    }
}

Both let text = ... and let number = ... are optional bindings in the context of the if-statement, and the if-block is only executed if both bindings succeed.

Trying to convert a hexadecimal text to a decimal in swift, but getting "Optional([num])" output

1 Answers1