How do I use subscript and superscript in Swift?

Most of the answers+examples are in ObjC, but this is how to do it in Swift.

let font:UIFont? = UIFont(name: "Helvetica", size:20)
let fontSuper:UIFont? = UIFont(name: "Helvetica", size:10)
let attString:NSMutableAttributedString = NSMutableAttributedString(string: "6.022*1023", attributes: [.font:font!])
attString.setAttributes([.font:fontSuper!,.baselineOffset:10], range: NSRange(location:8,length:2))
labelVarName.attributedText = attString

This gives me:

In a more detailed explanation:

1. Get UIFont you want for both the default and superscript style, superscript must be smaller.
2. Create a NSMutableAttributedString with the full string and default font.
3. Add an attribute to the characters you want to change (NSRange), with the smaller/subscript UIFont, and the NSBaselineOffsetAttributeName value is the amount you want to offset it vertically.
4. Assign it to your UILabel

Hopefully this helps other Swift devs as I needed this as well.

As a different approach, I wrote a function that takes in a string where the exponents are prepended with ^ such as 2^2•3•5^2 and returns 2²•3•5²

func exponentize(str: String) -> String {

    let supers = [
        "1": "\u{00B9}",
        "2": "\u{00B2}",
        "3": "\u{00B3}",
        "4": "\u{2074}",
        "5": "\u{2075}",
        "6": "\u{2076}",
        "7": "\u{2077}",
        "8": "\u{2078}",
        "9": "\u{2079}"]

    var newStr = ""
    var isExp = false
    for (_, char) in str.characters.enumerate() {
        if char == "^" {
            isExp = true
        } else {
            if isExp {
                let key = String(char)
                if supers.keys.contains(key) {
                    newStr.append(Character(supers[key]!))
                } else {
                    isExp = false
                    newStr.append(char)
                }
            } else {
                newStr.append(char)
            }
        }
    }
    return newStr
}

It's a bit of a brute force method, but it works if you don't want to deal with attributed strings or you want your string to be independent of a font.

If you can get along with text that doesn't look perfect, and only need a subset of characters you can make use of the unicode superscript and subscript numbers: ⁰ ¹ ² ³ ⁴ ⁵ ⁶ ⁷ ⁸ ⁹ ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ This has the advantage of being a lot less cumbersome.

I wrote the following extension or you can use it as a function, it is working well for me . you can modify it by skipping the parts that are not essential to you

extension NSMutableAttributedString
{
enum scripting : Int
{
    case aSub = -1
    case aSuper = 1
}

func characterSubscriptAndSuperscript(string:String,
                                      characters:[Character],
                                      type:scripting,
                                      fontSize:CGFloat,
                                      scriptFontSize:CGFloat,
                                      offSet:Int,
                                      length:[Int],
                                      alignment:NSTextAlignment)-> NSMutableAttributedString
{
    let paraghraphStyle = NSMutableParagraphStyle()
     // Set The Paragraph aligmnet , you can ignore this part and delet off the function
    paraghraphStyle.alignment = alignment

    var scriptedCharaterLocation = Int()
    //Define the fonts you want to use and sizes
    let stringFont = UIFont.boldSystemFont(ofSize: fontSize)
    let scriptFont = UIFont.boldSystemFont(ofSize: scriptFontSize)
     // Define Attributes of the text body , this part can be removed of the function
    let attString = NSMutableAttributedString(string:string, attributes: [NSFontAttributeName:stringFont,NSForegroundColorAttributeName:UIColor.black,NSParagraphStyleAttributeName: paraghraphStyle])

    // the enum is used here declaring the required offset
    let baseLineOffset = offSet * type.rawValue
    // enumerated the main text characters using a for loop
    for (i,c) in string.characters.enumerated()
    {
        // enumerated the array of first characters to subscript
        for (theLength,aCharacter) in characters.enumerated()
        {
            if c == aCharacter
            {
               // Get to location of the first character
                scriptedCharaterLocation = i
              //Now set attributes starting from the character above     
               attString.setAttributes([NSFontAttributeName:scriptFont,
              // baseline off set from . the enum i.e. +/- 1          
              NSBaselineOffsetAttributeName:baseLineOffset,
              NSForegroundColorAttributeName:UIColor.black],
               // the range from above location 
        range:NSRange(location:scriptedCharaterLocation,
         // you define the length in the length array 
         // if subscripting at different location 
         // you need to define the length for each one
         length:length[theLength]))

            }
        }
    }
    return attString}
  }

examples:

let attStr1 = NSMutableAttributedString().characterSubscriptAndSuperscript(
               string: "23 x 456", 
               characters:["3","5"], 
               type: .aSuper, 
               fontSize: 20, 
               scriptFontSize: 15, 
               offSet: 10, 
               length: [1,2], 
               alignment: .left)

let attStr2 = NSMutableAttributedString().characterSubscriptAndSuperscript(
           string: "H2SO4", 
           characters: ["2","4"], 
           type: .aSub, 
           fontSize: 20, 
           scriptFontSize: 15, 
            offSet: 8, 
           length: [1,1], 
           alignment: .left)