Swift 2. Trying to unwrap a label.text! with NSNumberFormatter() included - swift2

Question

Swift 2. I'm trying to use the answer of a label.text! to multiply again. The label is an optional but it has to be multiplied with a Double.
#IBOutlet weak var testLabel: UILabel!
#IBOutlet weak var first: UITextField!
#IBOutlet weak var second: UITextField!
func calculation1() {
let dfirst = Double(first.text!)
let dsecond = Double(second.text!)
if dfirst != nil && dsecond != nil {
let answerCal = ceil(dfirst! * dsecond!)
let numberFormatter = NSNumberFormatter()
numberFormatter.numberStyle = .DecimalStyle
testLabel.text = numberFormatter.stringFromNumber(answerCal)
}
}
Any help will be appreciated.

Answer 1

First of all, apologies as I've put this together on a tablet meaning I cannot access the code editor. However, here's my take on your problem:
#IBOutlet weak var testLabel: UILabel!
#IBOutlet weak var first: UITextField!
#IBOutlet weak var second: UITextField!
func calculation1() -> Void {
// Check our two text fields contain text
guard let _ = first.text,
let _ = second.text else { return }
c // Check that the text can be parsed as Doubles
c guard let dfirst : Double = Double(first.text!),
let dsecond : Double = Double(second.text!) else { return }
// Now that we know we have two valid numbers, do the calculation
let answerCal : Double = ceil(dfirst! * dsecond!)
// Fetch a number formatter
let numberFormatter : NSNumberFormatter = {
let nF : NSNumberFormatter = NSNumberFormatter()
nF.numberStyle = .DecimalStyle
return nF
}()
// And update the text field with the answer if it produces a valid result
if let answerText : String = numberFormatter.stringFromNumber(answerCal) {
testLabel.text = answerText
}
}
You've got to be careful with UI elements where the user can theoretically type in anything and crash your app if you don't check it first. Hence the guard statements that will safely exit the method call if there is no text in the text fields or if those fields contain unusable text.
The reason you're getting an Optional back from your number formatter is because there is no guarantee that the formatter will be able to give you a valid string. Therefore you'll see that I've explicitly checked that the numbe formatter does generate a non-nil result before trying to update the text field.
(Note - I appreciate the closure for the number formatter is technically surplus to requirements but I find it clearer sometimes when configuring an object.)
UPDATE:
Vidal - did you try the code I sent you? I've quickly knocked up the following which is based on what I put together last night. It is obviously crude but shows that the methodology I suggested works fine, unless I'm missing something. The only issue I can think of is that you've done something in interface builder which I'm unaware of. Hope that helps!
import UIKit
class ViewController: UIViewController {
var calculatorView : UIView!
var textFieldOne : UITextField!
var textFieldTwo : UITextField!
var calButton : UIButton!
var answer : UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.calculatorView = {
let cV : UIView = UIView(frame: CGRect(origin: CGPointZero, size: CGSizeMake(400, 400)))
cV.backgroundColor = UIColor.redColor()
func buildTextField() -> UITextField {
let tF : UITextField = UITextField()
tF.backgroundColor = UIColor.whiteColor()
tF.textColor = UIColor.blackColor()
tF.placeholder = "Please enter number"
return tF
}
self.textFieldOne = buildTextField()
self.textFieldTwo = buildTextField()
self.textFieldOne.frame = CGRect(origin: CGPointMake(20, 20), size: CGSizeMake(160, 50))
self.textFieldTwo.frame = CGRect(origin: CGPointMake(220, 20), size: CGSizeMake(160, 50))
self.calButton = {
let cB : UIButton = UIButton()
cB.setTitle("Calculate", forState: .Normal)
cB.frame = CGRect(origin: CGPointMake(20, 80), size: CGSizeMake(360, 50))
cB.addTarget(self, action: #selector(self.getAnswer), forControlEvents: UIControlEvents.TouchUpInside)
return cB
}()
self.answer = {
let a : UILabel = UILabel()
a.backgroundColor = UIColor.blueColor()
a.textColor = UIColor.whiteColor()
a.frame = CGRect(origin: CGPointMake(20, 140), size: CGSizeMake(360, 50))
return a
}()
cV.addSubview(textFieldOne)
cV.addSubview(textFieldTwo)
cV.addSubview(calButton)
cV.addSubview(answer)
return cV
}()
self.view.addSubview(calculatorView)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func getAnswer() -> Void {
// Check our two text fields contain text
guard let _ = self.textFieldOne.text,
let _ = self.textFieldTwo.text else { return }
// Check that the text can be parsed as Doubles
guard let dfirst : Double = Double(self.textFieldOne.text!),
let dsecond : Double = Double(self.textFieldTwo.text!) else { return }
// Now that we know we have two valid numbers, do the calculation
let answerCal : Double = ceil(dfirst * dsecond)
// Fetch a number formatter
let numberFormatter : NSNumberFormatter = {
let nF : NSNumberFormatter = NSNumberFormatter()
nF.numberStyle = .DecimalStyle
return nF
}()
// And update the text field with the answer if it produces a valid result
if let answerText : String = numberFormatter.stringFromNumber(answerCal) {
self.answer.text = answerText
}
}
}