How do I make an attributed string using Swift?

Question

I am trying to make a simple Coffee Calculator. I need to display the amount of coffee in grams. The "g" symbol for grams needs to be attached to my UILabel that I am using to display the amount. The numbers in the UILabel are changing dynamically with user input just fine, but I need to add a lower case "g" on the end of the string that is formatted differently from the updating numbers. The "g" needs to be attached to the numbers so that as the number size and position changes, the "g" "moves" with the numbers. I'm sure this problem has been solved before so a link in the right direction would be helpful as I've googled my little heart out.

I've searched through the documentation for an attributed string and I even downloded an "Attributed String Creator" from the app store, but the resulting code is in Objective-C and I am using Swift. What would be awesome, and probably helpful to other developers learning this language, is a clear example of creating a custom font with custom attributes using an attributed string in Swift. The documentation for this is very confusing as there is not a very clear path on how to do so. My plan is to create the attributed string and add it to the end of my coffeeAmount string.

var coffeeAmount: String = calculatedCoffee + attributedText

Where calculatedCoffee is an Int converted to a string and "attributedText" is the lowercase "g" with customized font that I am trying to create. Maybe I'm going about this the wrong way. Any help is appreciated!

Answer 1

This answer has been updated for Swift 4.2.

Quick Reference

The general form for making and setting an attributed string is like this. You can find other common options below.

// create attributed string
let myString = "Swift Attributed String"
let myAttribute = [ NSAttributedString.Key.foregroundColor: UIColor.blue ]
let myAttrString = NSAttributedString(string: myString, attributes: myAttribute) 

// set attributed text on a UILabel
myLabel.attributedText = myAttrString

let myAttribute = [ NSAttributedString.Key.foregroundColor: UIColor.blue ]

let myAttribute = [ NSAttributedString.Key.backgroundColor: UIColor.yellow ]

let myAttribute = [ NSAttributedString.Key.font: UIFont(name: "Chalkduster", size: 18.0)! ]

let myAttribute = [ NSAttributedString.Key.underlineStyle: NSUnderlineStyle.single.rawValue ]

let myShadow = NSShadow()
myShadow.shadowBlurRadius = 3
myShadow.shadowOffset = CGSize(width: 3, height: 3)
myShadow.shadowColor = UIColor.gray

let myAttribute = [ NSAttributedString.Key.shadow: myShadow ]

The rest of this post gives more detail for those who are interested.

---

Attributes

String attributes are just a dictionary in the form of [NSAttributedString.Key: Any], where NSAttributedString.Key is the key name of the attribute and Any is the value of some Type. The value could be a font, a color, an integer, or something else. There are many standard attributes in Swift that have already been predefined. For example:

• key name: NSAttributedString.Key.font, value: a UIFont
• key name: NSAttributedString.Key.foregroundColor, value: a UIColor
• key name: NSAttributedString.Key.link, value: an NSURL or NSString

There are many others. See this link for more. You can even make your own custom attributes like:

• key name: NSAttributedString.Key.myName, value: some Type.
  if you make an extension:

  extension NSAttributedString.Key {
      static let myName = NSAttributedString.Key(rawValue: "myCustomAttributeKey")
  }
  

Creating attributes in Swift

You can declare attributes just like declaring any other dictionary.

// single attributes declared one at a time
let singleAttribute1 = [ NSAttributedString.Key.foregroundColor: UIColor.green ]
let singleAttribute2 = [ NSAttributedString.Key.backgroundColor: UIColor.yellow ]
let singleAttribute3 = [ NSAttributedString.Key.underlineStyle: NSUnderlineStyle.double.rawValue ]

// multiple attributes declared at once
let multipleAttributes: [NSAttributedString.Key : Any] = [
    NSAttributedString.Key.foregroundColor: UIColor.green,
    NSAttributedString.Key.backgroundColor: UIColor.yellow,
    NSAttributedString.Key.underlineStyle: NSUnderlineStyle.double.rawValue ]

// custom attribute
let customAttribute = [ NSAttributedString.Key.myName: "Some value" ]

Note the rawValue that was needed for the underline style value.

Because attributes are just Dictionaries, you can also create them by making an empty Dictionary and then adding key-value pairs to it. If the value will contain multiple types, then you have to use Any as the type. Here is the multipleAttributes example from above, recreated in this fashion:

var multipleAttributes = [NSAttributedString.Key : Any]()
multipleAttributes[NSAttributedString.Key.foregroundColor] = UIColor.green
multipleAttributes[NSAttributedString.Key.backgroundColor] = UIColor.yellow
multipleAttributes[NSAttributedString.Key.underlineStyle] = NSUnderlineStyle.double.rawValue

Attributed Strings

Now that you understand attributes, you can make attributed strings.

Initialization

There are a few ways to create attributed strings. If you just need a read-only string you can use NSAttributedString. Here are some ways to initialize it:

// Initialize with a string only
let attrString1 = NSAttributedString(string: "Hello.")

// Initialize with a string and inline attribute(s)
let attrString2 = NSAttributedString(string: "Hello.", attributes: [NSAttributedString.Key.myName: "A value"])

// Initialize with a string and separately declared attribute(s)
let myAttributes1 = [ NSAttributedString.Key.foregroundColor: UIColor.green ]
let attrString3 = NSAttributedString(string: "Hello.", attributes: myAttributes1)

If you will need to change the attributes or the string content later, you should use NSMutableAttributedString. The declarations are very similar:

// Create a blank attributed string
let mutableAttrString1 = NSMutableAttributedString()

// Initialize with a string only
let mutableAttrString2 = NSMutableAttributedString(string: "Hello.")

// Initialize with a string and inline attribute(s)
let mutableAttrString3 = NSMutableAttributedString(string: "Hello.", attributes: [NSAttributedString.Key.myName: "A value"])

// Initialize with a string and separately declared attribute(s)
let myAttributes2 = [ NSAttributedString.Key.foregroundColor: UIColor.green ]
let mutableAttrString4 = NSMutableAttributedString(string: "Hello.", attributes: myAttributes2)

Changing an Attributed String

As an example, let's create the attributed string at the top of this post.

First create an NSMutableAttributedString with a new font attribute.

let myAttribute = [ NSAttributedString.Key.font: UIFont(name: "Chalkduster", size: 18.0)! ]
let myString = NSMutableAttributedString(string: "Swift", attributes: myAttribute )

If you are working along, set the attributed string to a UITextView (or UILabel) like this:

textView.attributedText = myString

You don't use textView.text.

Here is the result:

Then append another attributed string that doesn't have any attributes set. (Notice that even though I used let to declare myString above, I can still modify it because it is an NSMutableAttributedString. This seems rather unSwiftlike to me and I wouldn't be surprised if this changes in the future. Leave me a comment when that happens.)

let attrString = NSAttributedString(string: " Attributed Strings")
myString.append(attrString)

Next we'll just select the "Strings" word, which starts at index 17 and has a length of 7. Notice that this is an NSRange and not a Swift Range. (See this answer for more about Ranges.) The addAttribute method lets us put the attribute key name in the first spot, the attribute value in the second spot, and the range in the third spot.

var myRange = NSRange(location: 17, length: 7) // range starting at location 17 with a lenth of 7: "Strings"
myString.addAttribute(NSAttributedString.Key.foregroundColor, value: UIColor.red, range: myRange)

Finally, let's add a background color. For variety, let's use the addAttributes method (note the s). I could add multiple attributes at once with this method, but I will just add one again.

myRange = NSRange(location: 3, length: 17)
let anotherAttribute = [ NSAttributedString.Key.backgroundColor: UIColor.yellow ]
myString.addAttributes(anotherAttribute, range: myRange)

Notice that the attributes are overlapping in some places. Adding an attribute doesn't overwrite an attribute that is already there.

Related

• How to change the text of an NSMutableAttributedString but keep the attributes

Further Reading

• How to retrieve the attributes from a tap location
• Attributed String Programming Guide (very informative but unfortunately only in Objective-C)