的
NSString版本（与Swift String相对）
replacingCharacters(in: NSRange, with:NSString)接受an
NSRange，因此一个简单的解决方案是将其 转换
String为
NSStringfirst。在Swift3和2中，委托和替换方法的名称略有不同，因此取决于您使用的是哪种Swift：
UITextField3.0
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool { let nsString = textField.text as NSString? let newString = nsString?.replacingCharacters(in: range, with: string)}UITextField2.x
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { let nsString = textField.text as NSString? let newString = nsString?.stringByReplacingCharactersInRange(range, withString: string)}
