Swift 2 Converting from String To Number

Question

I'm following the Stanford Videos for iOS development and I am using Xcode 7 with Swift 2. I wrote the code from the video line by line, however I keep getting an error.

import UIKit

class ViewController: UIViewController
{

@IBOutlet weak var display: UILabel!

var userIsTyping = false

@IBAction func AppendDigit(sender: UIButton) {
    let digit = sender.currentTitle!
    if userIsTyping {
        display.text = display.text! + digit
    } else {
        display.text = digit
        userIsTyping = true
    }
}

var operandStack = Array<Double>()

@IBAction func enter() {
    userIsTyping = false
    operandStack.append(displayValue)
}

var displayValue: Double {
    get{
        return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
    }
    set (newValue){
        display.text = "\(newValue)"
        userIsTyping = false

    }
}


}

At the line where I return

NumberFormatter().numberFromString(display.text!)!.doubleValue

I get an error of

Thread 1: EXC_BAD_INSTRUCTION(code=EXC_1386_INVOP,subcode=0x0)

Your label display is nil or contains not-number-string.

truongky
– truongky

2015-12-25 02:23:16 +00:00
Commented Dec 25, 2015 at 2:23 — truongky
– truongky, Commented Dec 25, 2015 at 2:23

gnasher729 · Accepted Answer · 2015-12-24 20:39:50Z

1

A conversion can fail. The result can be nil. The "!" means "compiler, I am 100 percent sure that the result can never be nil, so if it is ever nil then please crash". Guess what, sometimes it is nil.

Use "if let".

PS. I think it is very, very unhealthy to take user interface elements (like the title of a button) and to assume they have certain values.

answered Dec 24, 2015 at 20:39

gnasher729

53k5 gold badges83 silver badges106 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Nicolas Miari Over a year ago

Indeed. There is this thing called "user input sanitation/validation".

LIProf · Accepted Answer · 2015-12-24 20:46:04Z

0

You are much better off substituting that return statement with a much simpler:

return Double(display.text!)!

answered Dec 24, 2015 at 20:46

LIProf

4362 silver badges5 bronze badges

Comments

pradip kikani · Accepted Answer · 2015-12-25 05:12:16Z

0

let Number = (NSNumberFormatter().numberFromString(xtxt.text!)as! Double)

 return Number

answered Dec 25, 2015 at 5:12

pradip kikani

6376 silver badges14 bronze badges

Collectives™ on Stack Overflow

Swift 2 Converting from String To Number

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related