ios - 强制小写字母-iOS Swift

我想在用户键入时在UITextfield中强制小写。
到目前为止，我已经有了这段代码，但似乎并没有降低字符。

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    if string.characters.count == 0 {
        return true
    }

    let currentText = textField.text ?? ""
    let prospectiveText = (currentText as NSString).stringByReplacingCharactersInRange(range, withString: string.lowercaseString)

    switch textField {
    // Allow only lower-case vowels in this field,
    // and limit its contents to a maximum of 6 characters.
    case userNameTextField:
        return prospectiveText.characters.count <= 27
    default:
        return true
    }
}

最佳答案

首先，您应该在文本字段上设置以下属性以限制自动大写:

textfield.autocapitalizationType = UITextAutocapitalizationType.None

这是您可以进一步限制它的方法:

func textField(textField: UITextField!, shouldChangeCharactersInRange range: NSRange, replacementString string: String!) -> Bool {

    if let _ = string.rangeOfCharacterFromSet(NSCharacterSet.uppercaseLetterCharacterSet()) {
        // Do not allow upper case letters
        return false
    }

    return true
}

更新为SWIFT 4

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    if let _ = string.rangeOfCharacter(from: .uppercaseLetters) {
        // Do not allow upper case letters
        return false
    }

    return true
}