Swift 5.0

extension UIButton{
   func addTextSpacing(_ spacing: CGFloat){
       let attributedString = NSMutableAttributedString(string: title(for: .normal) ?? "")
       attributedString.addAttribute(NSAttributedString.Key.kern, value: spacing, range: NSRange(location: 0, length: attributedString.string.count))
       self.setAttributedTitle(attributedString, for: .normal)
   }
}
button.addTextSpacing(1)

extension UILabel{
    func addTextSpacing(_ spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.text ?? "")
        attributedString.addAttribute(NSAttributedString.Key.kern, value: spacing, range: NSRange(location: 0, length: attributedString.string.count))
        self.attributedText = attributedString
    }
}
label.addTextSpacing(1)

extension UITextField{
    func addPlaceholderSpacing(_ spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.placeholder ?? "")
        attributedString.addAttribute(NSAttributedString.Key.kern, value: spacing, range: NSRange(location: 0, length: attributedString.string.count))
        self.attributedPlaceholder = attributedString
    }
}
textField.addPlaceholderSpacing(1)

extension UINavigationItem{
    func addSpacing(_ spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.title ?? "")
        attributedString.addAttribute(NSAttributedString.Key.kern, value: spacing, range: NSRange(location: 0, length: attributedString.string.count))
        let label = UILabel()
        label.textColor = UIColor.black
        label.font = UIFont.systemFont(ofSize: 15, weight: .bold)
        label.attributedText = attributedString
        label.sizeToFit()
        self.titleView = label
    }
}
navigationItem.addSpacing(1)

1.使NSAttributedString像你链接的问题
1.在UIButton上调用setAttributedTitle(_ ,forState:)
试试这个（未测试）：

let title = agreementButton.titleForState(.Normal)
let attributedTitle = NSAttributedString(string: title, attributes: [NSKernAttributeName: 1.0])
agreementButton.setAttributedTitle(attributedTitle, forState: .Normal)

Swift 4酒店

extension UIButton{

    func addTextSpacing(_ letterSpacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: (self.titleLabel?.text!)!)
        attributedString.addAttribute(NSAttributedString.Key.kern, value: letterSpacing, range: NSRange(location: 0, length: (self.titleLabel?.text!.count)!))
        self.setAttributedTitle(attributedString, for: .normal)
    }

}

// Usage: button.addTextSpacing(5.0)

不是一个完整的答案，而是一个GOTCHA和一个FIX。
GOTCHA：应用字符间距也会将空格添加到文本的END。此错误功能/错误意味着居中对齐的文本将错误显示。
FIX：当为属性化文本创建Range时，从text.count值中减去1（因此忽略字符串中的最后一个字符以用于间距目的）
例如，由于额外空间而导致不正确的居中：

固定：

[编辑]
与此相关的是，如果使用EdgeInsets在文本周围添加填充，则UIButton子类将需要覆盖intrinsicContentsSize:

override open var intrinsicContentSize: CGSize {
    let size = super.intrinsicContentSize
    let insets = self.titleEdgeInsets
    let width = size.width + insets.left + insets.right
    let height = size.height + insets.top + insets.bottom
    return CGSize(width: width, height: height)
}

Swift 5扩展名在此。

extension UIButton {
    @IBInspectable
    var letterSpacing: CGFloat {
        set {
            let attributedString: NSMutableAttributedString
            if let currentAttrString = attributedTitle(for: .normal) {
                attributedString = NSMutableAttributedString(attributedString: currentAttrString)
            }
            else {
                attributedString = NSMutableAttributedString(string: self.title(for: .normal) ?? "")
                setTitle(.none, for: .normal)
            }

            attributedString.addAttribute(NSAttributedString.Key.kern, value: newValue, range: NSRange(location: 0, length: attributedString.length))
            setAttributedTitle(attributedString, for: .normal)
        }
        get {
            if let currentLetterSpace = attributedTitle(for: .normal)?.attribute(NSAttributedString.Key.kern, at: 0, effectiveRange: .none) as? CGFloat {
                return currentLetterSpace
            }
            else {
                return 0
            }
        }
    }
}

用法：您可以在脚本上或通过代码设置字母间距。

button.letterSpacing = 2.0

Code Different的解决方案不支持文本颜色设置。也可以重写UIButton类，使间距参数甚至在情节提要中也可用。下面是一个更新的Swift 3解决方案：

*Swift 3酒店，纽约

class UIButtonWithSpacing : UIButton
{
    override func setTitle(_ title: String?, for state: UIControlState)
    {
        if let title = title, spacing != 0
        {
            let color = super.titleColor(for: state) ?? UIColor.black
            let attributedTitle = NSAttributedString(
                string: title,
                attributes: [NSKernAttributeName: spacing,
                             NSForegroundColorAttributeName: color])
            super.setAttributedTitle(attributedTitle, for: state)
        }
        else
        {
            super.setTitle(title, for: state)
        }
    }

    fileprivate func updateTitleLabel_()
    {
        let states:[UIControlState] = [.normal, .highlighted, .selected, .disabled]
        for state in states
        {
            let currentText = super.title(for: state)
            self.setTitle(currentText, for: state)
        }
    }

    @IBInspectable var spacing:CGFloat = 0 {
        didSet {
            updateTitleLabel_()
        }
    }
}

基于jaya raj的答案更新Swift 4。

extension UIButton{
    func addTextSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: (self.titleLabel?.text!)!)
        attributedString.addAttribute(NSAttributedStringKey.kern, value: spacing, range: NSRange(location: 0, length: (self.titleLabel?.text!.characters.count)!))
        self.setAttributedTitle(attributedString, for: .normal)
    }
}

extension UILabel{
    func addTextSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.text!)
        attributedString.addAttribute(NSAttributedStringKey.kern, value: spacing, range: NSRange(location: 0, length: self.text!.characters.count))
        self.attributedText = attributedString
    }
}

extension UITextField{
    func addPlaceholderSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.placeholder!)
        attributedString.addAttribute(NSAttributedStringKey.kern, value: spacing, range: NSRange(location: 0, length: self.placeholder!.characters.count))
        self.attributedPlaceholder = attributedString
    }
}

extension UINavigationItem{
    func addSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.title!)
        attributedString.addAttribute(NSAttributedStringKey.kern, value: spacing, range: NSRange(location: 0, length: self.title!.characters.count))
        let label = UILabel()
        label.textColor = UIColor.black
        label.font = UIFont.systemFont(ofSize: 15, weight: UIFont.Weight.bold)
        label.attributedText = attributedString
        label.sizeToFit()
        self.titleView = label
    }
}

Swift 5不强制解包更新：

我觉得这是一个更好的解决方案，因为我们迎合现有的属性按钮以及

func addTextSpacing(_ letterSpacing: CGFloat) {
    let attributedString = attributedTitle(for: .normal)?.mutableCopy() as? NSMutableAttributedString ??
        NSMutableAttributedString(string: title(for: .normal) ?? "")
    attributedString.addAttribute(NSAttributedString.Key.kern, value: letterSpacing,
                                  range: NSRange(location: 0, length: attributedString.string.count))
    self.setAttributedTitle(attributedString, for: .normal)
}

Swift 5

guard let buttonTitle = button.title(for: .normal) else { return }
    
    let attributedTitle = NSAttributedString(string: buttonTitle, attributes: [NSAttributedString.Key.kern: kernValue])
    button.setAttributedTitle(attributedTitle, for: .normal)