Swift converting string to double with numberformatter returns nil

Question

I am trying to convert the value of a text field, which the user enters. As users are able to enter decimal values in european number format too, I use numberformatter for that. This was what I was trying:

let newprice = MaximumPriceLabel.text as! String
print(newprice) -> result: Optional("10,00")
print(formatter.number(from: newprice as String)) -> result: nil
print(Double(formatter.number(from: ("10,11"))!)) -> result: 10.11 -> that is what I want

So there is a value stored in the variable newprice, but when formatting, it returns nil. When I test it with a manual value, it works. Is there anything I am doing wrong? Formatter.local is set to Locale.current.

Update: The problem seems to be that the MaximumPriceLabel.text contains not only the value I need, but really the text "Optional("10,00") - which fails when converting to a number. The value is filled like this:

 self.MaximumPriceLabel.text = String(describing: formatter.string(from: NSNumber(value: desprice)))

and when I do a print afterwards, I receive "Optional("Optional(\"10,00\")")" -> even when I clear the variable MaximumPriceLabel.text first.

Unrelated but why do you cast the `text` property which is defined as `String(?)` to `String` and later once again to `String`? — vadian, Oct 22 '17 at 20:32
Based on your comments below my answer, you need to update your question with the code that sets the `text` property of your `MaximumPriceLabel` label. It seems your label actually contains the text `Optional(...)` and of course such text isn't a valid number. So your solution is to fix the code that sets the label so the label's text only contains the number itself and not the `Optional(...)` part. — rmaddy, Oct 23 '17 at 15:32
And what is this `desprice` variable? How is it declared/initialized? — rmaddy, Oct 23 '17 at 15:44
When I print desprice, I get 10.0. desprice is filled by a function with a return value of type double. let desprice = getDesiredPrice(checkString: myVariables.ASIN) — Alexander Ko, Oct 23 '17 at 15:48
That fixed it! Thanks a lot for your kind help, to all of you guys. — Alexander Ko, Oct 23 '17 at 15:57

rmaddy · Accepted Answer · 2017-10-23T15:50:45.843

1

You need to learn how to deal with optionals.

Your first issue is how you set the label's text. Please note that NumberFormatter string(from:) returns an optional String. And never, never use String(describing:) to display information to a user. That should only be used for debugging.

Start by changing:

self.MaximumPriceLabel.text = String(describing: formatter.string(from: NSNumber(value: desprice)))

to:

if let text = formatter.string(from: NSNumber(value: desprice)) {
    MaximumPriceLabel.text = text
}

That will fix the issue of the label's text having the text Optional(...).

Then your code for converting the label's text back to a string needs to be updated as:

if let newprice = MaximumPriceLabel.text {
    if let price = formatter.number(from: newprice) {
        print("The price is \(price)")
    } else {
        print("Invalid number: \(newprice)")
    }
}

edited Oct 23 '17 at 15:50

answered Oct 22 '17 at 20:31

rmaddy

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I tried this - and I get "Invalid number: Optional("10,00")" - and I don't understand why :( – Alexander Ko Oct 23 '17 at 15:18
It seems that your label actually has the text `Optional(...)` in it. Obviously such text isn't a valid number. How do you set the label's text? – rmaddy Oct 23 '17 at 15:24
This could be. It is filled by user input, from a decimal keyboard. – Alexander Ko Oct 23 '17 at 15:26
That doesn't answer my question. What code do you use to set the label's text? – rmaddy Oct 23 '17 at 15:27

Swift converting string to double with numberformatter returns nil

1 Answers1