将字体添加到 NSMutableAttributedString 缺少 .font 属性的位置

Question

I want to apply a specific font to an NSMutableAttributedString where no .font attribute is applied. How could I achieve that? I tried enumerating the attributes that contain a font and extracting the ranges but I am kind of lost to the complexity of finding the ranges that don't contain a font attribute since I think I must handle intersections or possible unknown scenarios. Is there a simple way to do it? What I did until now:

        var allRangesWithFont = [NSRange]()
        let stringRange = NSRange(location: 0, length: length)
        
        beginEditing()
        enumerateAttribute(.font,
                           in: stringRange,
                           options: .longestEffectiveRangeNotRequired) { (value, range, stop) in
            
            if let f = value as? UIFont {
                allRangesWithFont.append(range)
            }
        }

Answer 1

Change your way of thinking, instead, check if the font is not there, and apply your new font directly.

With attrStr being your NSMutableAttributedString , and newFont the font you want to apply.

let newFont = UIFont.italicSystemFont(ofSize: 15)
attrStr.enumerateAttribute(.font, in: NSRange(location: 0, length: attrStr.length), options: []) { value, subrange, pointeeStop in
    guard value == nil else { return }
    attrStr.addAttribute(.font, value: newFont, range: subrange)
}