如何在Swift中更改UIButton的字母间距？

我已经找到了如何将字母间距设置为UILabel(此处),但此方法不适用于UIButtons.有谁知道怎么做？

这是我正在使用的代码

    let buttonString = agreementButton.attributedTitleForState(.Normal) as! NSMutableAttributedString
    buttonString.addAttribute(NSKernAttributeName, value: 1.0, range: NSMakeRange(0, buttonString.length))
    agreementButton.setAttributedTitle(buttonString, forState: .Normal)

它抛出了一个错误: 'NSConcreteAttributedString' (0x19e508660) to 'NSMutableAttributedString' (0x19e506a40).

Swift 3.0

extension UIButton{
   func addTextSpacing(spacing: CGFloat){
       let attributedString = NSMutableAttributedString(string: (self.titleLabel?.text!)!)
       attributedString.addAttribute(NSKernAttributeName, value: spacing, range: NSRange(location: 0, length: (self.titleLabel?.text!.characters.count)!))
       self.setAttributedTitle(attributedString, for: .normal)
   }
}
btnRegister.addTextSpacing(spacing: 4.5)

extension UILabel{
    func addTextSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.text!)
        attributedString.addAttribute(NSKernAttributeName, value: spacing, range: NSRange(location: 0, length: self.text!.characters.count))
        self.attributedText = attributedString
    }
}
lblOne.addTextSpacing(spacing: 4.5)

extension UITextField{
    func addPlaceholderSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.placeholder!)
        attributedString.addAttribute(NSKernAttributeName, value: spacing, range: NSRange(location: 0, length: self.placeholder!.characters.count))
        self.attributedPlaceholder = attributedString
    }
}
txtUserName.addPlaceholderSpacing(spacing: 4.5)

extension UINavigationItem{
    func addSpacing(spacing: CGFloat){
        let attributedString = NSMutableAttributedString(string: self.title!)
        attributedString.addAttribute(NSKernAttributeName, 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: UIFontWeightBold)
        label.attributedText = attributedString
        label.sizeToFit()
        self.titleView = label
    }
}
navigationItem.addSpacing(spacing: 2.5)

NSAttributedString在你链接的问题中做出类似的话

打电话setAttributedTitle(_ ,forState:)给你UIButton

试试这个(未经测试):

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

斯威夫特4

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)