本意是限制輸入僅英文字母和數(shù)字，同時(shí)將字母轉(zhuǎn)為大寫。
測試發(fā)現(xiàn)了在修改的時(shí)候，每輸入一個(gè)字符，光標(biāo)都跑到最后，無法連續(xù)輸入修改。

解決辦法：

class CustomField {
// ...
addTarget(self, action: #selector(upperText), for: .editingChanged)
delegate = self
// ...
}

extension CustomField: UITextFieldDelegate {
    
    @objc private func upperText() {
        let textRange: UITextRange? = selectedTextRange
        text = text?.uppercased()
        selectedTextRange = textRange
    }
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        guard !string.isEmpty else {return true}
        
        let set: CharacterSet = CharacterSet(charactersIn: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")
            .inverted
        let result: String = string.components(separatedBy: set)
            .joined(separator: "")
        var valid: Bool = result == string
        let textFieldContent: String = (textField.text ?? "")
            .appending(string)
        if valid, textFieldContent.count > 10 {
            // 字符合法，但是追加后超出長度限制
            valid = false
        }
        return valid
    }
}