Looping Through Nsattributedstring Attributes to Increase Font Size

Looping Through NSAttributedString Attributes to Increase Font SIze

Something like this should work:

NSMutableAttributedString *res = [self.richTextEditor.attributedText mutableCopy];

[res beginEditing];
__block BOOL found = NO;
[res enumerateAttribute:NSFontAttributeName inRange:NSMakeRange(0, res.length) options:0 usingBlock:^(id value, NSRange range, BOOL *stop) {
if (value) {
UIFont *oldFont = (UIFont *)value;
UIFont *newFont = [oldFont fontWithSize:oldFont.pointSize * 2];
[res removeAttribute:NSFontAttributeName range:range];
[res addAttribute:NSFontAttributeName value:newFont range:range];
found = YES;
if (!found) {
// No font was found - do something else?
[res endEditing];
self.richTextEditor.attributedText = res;

At this point res has a new attributed string with all fonts being twice their original size.

How to set font size on NSAttributedString

let myString = "Swift Attributed String"
let myAttribute = [ NSForegroundColorAttributeName: UIColor.blue ]
let myAttrString = NSAttributedString(string: myString, attributes: myAttribute)

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


let myAttribute = [ NSFontAttributeName: UIFont(name: "Chalkduster", size: 18.0)! ]


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


let myAttribute = [ NSUnderlineStyleAttributeName: NSUnderlineStyle.StyleSingle.rawValue ]


let myAttribute = [ NSForegroundColorAttributeName: UIColor.blue ]

Background Color

let myAttribute = [ NSBackgroundColorAttributeName: UIColor.yellow ]

Change only fontsize of NSAttributedString

If you only want to change the size of any given font found in the attributed string then you can do:

let newStr = someAttributedString.mutableCopy() as! NSMutableAttributedString
newStr.enumerateAttribute(.font, in: NSRange(location: 0, length: newStr.string.utf16.count)) { (value, range, stop) in
if let oldFont = value as? UIFont {
let newFont = oldFont.withSize(20) // whatever size you need
newStr.addAttribute(.font, value: newFont, range: range)


This will keep all other attributes in place.

If you want to replace all fonts in a given attributed string with a single font of a given size but keep all other attributes such as bold and italic, see:
NSAttributedString, change the font overall BUT keep all other attributes?

NSAttributedString, change the font overall BUT keep all other attributes?

Since rmaddy's answer did not work for me (f.fontDescriptor.withFace(font.fontName) does not keep traits like bold), here is an updated Swift 4 version that also includes color updating:

extension NSMutableAttributedString {
func setFontFace(font: UIFont, color: UIColor? = nil) {
in: NSRange(location: 0, length: self.length)
) { (value, range, stop) in

if let f = value as? UIFont,
let newFontDescriptor = f.fontDescriptor
.withSymbolicTraits(f.fontDescriptor.symbolicTraits) {

let newFont = UIFont(
descriptor: newFontDescriptor,
size: font.pointSize
removeAttribute(.font, range: range)
addAttribute(.font, value: newFont, range: range)
if let color = color {
range: range
value: color,
range: range

Or, if your mix-of-attributes does not include font,

then you don't need to remove old font:

let myFont: UIFont = .systemFont(ofSize: UIFont.systemFontSize);

[NSAttributedString.Key.font: myFont],
range: NSRange(location: 0, length: myAttributedText.string.count));


The problem with f.fontDescriptor.withFace(font.fontName) is that it removes symbolic traits like italic, bold or compressed, since it will for some reason override those with default traits of that font face. Why this is so totally eludes me, it might even be an oversight on Apple's part; or it's "not a bug, but a feature", because we get the new font's traits for free.

So what we have to do is create a font descriptor that has the symbolic traits from the original font's font descriptor: .withSymbolicTraits(f.fontDescriptor.symbolicTraits). Props to rmaddy for the initial code on which I iterated.

I've already shipped this in a production app where we parse a HTML string via NSAttributedString.DocumentType.html and then change the font and color via the extension above. No problems so far.

Adjust font size of NSMutableAttributedString proportional to UILabel's frame height

Finally come up with an answer.

I created seperate custom UILabel subclass as follows:

class AttrLabel: UILabel {

// FIXME: - properties
var fontSize: CGFloat = 0
var frameHeight: CGFloat = 0

// FIXME: - proportional font size adjustment
override func layoutSubviews() {

guard let oldAttrText = attributedText else {

let mutableAttributedText = NSMutableAttributedString(attributedString: oldAttrText)

mutableAttributedText.enumerateAttribute(NSFontAttributeName, in: NSRange(location: 0, length: mutableAttributedText.length), options: []) { (_ value: Any?, _ range: NSRange, _ stop: UnsafeMutablePointer<ObjCBool>) in
if let attributeFont = value as? UIFont {
let newFont = attributeFont.withSize(self.frame.size.height * (self.fontSize / self.frameHeight))
mutableAttributedText.removeAttribute(NSFontAttributeName, range: range)
mutableAttributedText.addAttribute(NSFontAttributeName, value: newFont, range: range)

attributedText = mutableAttributedText


private let id: AttrLabel = {
let label = AttrLabel()
label.textAlignment = .left
label.numberOfLines = 1
label.fontSize = 17
label.frameHeight = 20
label.clipsToBounds = true
return label


let idStr = NSMutableAttributedString()
id.attributedText = idStr.attrStr(text: "BOLD TEXT: ", font: UIFont.systemFont(ofSize: 17, weight: .semibold), textColor: UIColor(hex: 0x212121, alpha: 1)).attrStr(text: "REGULAR WEIGHT TEXT.", font: UIFont.systemFont(ofSize: 17, weight: .regular), textColor: UIColor(hex: 0x212121, alpha: 1))

"Prajeet Shrestha's" extension for NSMutableAttributedString modified by me

extension NSMutableAttributedString {

func attrStr(text: String, font: UIFont, textColor: UIColor) -> NSMutableAttributedString {
let attributes: [String: Any] = [
NSFontAttributeName: font,
NSForegroundColorAttributeName: textColor
let string = NSMutableAttributedString(string: text, attributes: attributes)
return self

Example of NSAttributedString with two different font sizes?

You would do something like this…

NSMutableAttributedString *hogan = [[NSMutableAttributedString alloc] initWithString:@"Presenting the great... Hulk Hogan!"];
[hogan addAttribute:NSFontAttributeName
value:[UIFont systemFontOfSize:20.0]
range:NSMakeRange(24, 11)];

This will set the last two words in 20-point text; the rest of the string will use the default value (which I believe is 12 points). The thing that might be confusing about setting the text size is that you have to set the typeface and the size at the same time—each UIFont object encapsulates both of those properties.

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