Swift Converting Character to String

Question

I have an issue with converting character type to String type. First of all, I have below extension of String for finding nth character within String.

extension String {
    func characterAtIndex(index: Int) -> Character? {
        var cur = 0
        for char in self {
            if cur == index {
                return char
            }
            cur++
        }
        return nil
    }
}

I get what I want with this class extension. However when I use that nth character for title of my custom UIButton, gives an error. My Uibutton Class is

class hareketliHarfler: UIButton {
    init(frame: CGRect) {
        super.init(frame: frame)
        // Initialization code
    }
    func getLetter(letter:String!){
        self.titleLabel.text = letter 
    }
}

The error show when i try to access "getLetter(letter:String)" function. Here is example of main view Controller codes:

    var harfim = hareketliHarfler(frame: CGRectMake(100,100,100,100))
var str="This is my String"
var bufi=str.characterAtIndex(3)
    harfim.getLetter(bufi as AnyObject) ****

In * section I try .getLetter(bufi), .getLetter(bufi as String) also I try to change parameter type of function. Look like: func getLetter(letter:Character!) or func getLetter(letter:AnyObject!)...etc Didn't find a way. Need a help on that. Thank you

Instructor

Please don't subvert the Swift String and Character types with "C" like tricks. There are methods in Swift to handle these things correctly and by that I mean all unicode characters. – Tyburn

When asking about an error message, it's really helpful to post the text of the error message. – Nasturtium

Answer 1

Your problem is quite simple: your characterAtIndex function returns a Character, and self.titleLabel.text is a String. You can't convert between the two implicitly. The easiest way would be to turn the Character into a String using the String initialiser:

// ch will be Character? type.
if let ch = str.characterAtIndex(3) {
    // Initialise a new String containing the single character 'ch'
    harfim.getLetter(String(ch))
} else {
    // str didn't have a third character.
}

Unlike other solutions, this is safe for unusual Unicode characters, and won't initialise a potentially large array or iterate the whole String just to get the third character.

Nasturtium

Answer 2

How about the simple String(theCharacter)

Works in Swift 4 and Swift 5

Proposition

Answer 3

Change this:

var bufi=str.characterAtIndex(3)
harfim.getLetter(bufi as AnyObject)

to this:

harfim.getLetter(String(Array(str)[3]))

So what happening here:

1. we create an array from our string. Array elements are symbols from original string. Such break down correctly tracks symbols that are presented with a sequences of two or more code points. E.g. emoji or flag as noted by @MartinR.

2. We access element at 4-th position.

Note that as we crate an array from initial string then performance wise is better to use this method only with short strings and avoid it in oft-repeated routines. But in your case it seems to be OK.

Aguiar

Since at least Beta 4 converting a String to an Array correctly handles utf characters that are composed of multiple utf-16 components. – Tyburn

Answer 4

Can also use Character(text).isNumber if you want to get localised numbers.

Reference: https://developer.apple.com/documentation/swift/character/3127015-isnumber

Ezekielezell