Android 字符串要求长度4-16,且只允许包含字母、数字、下划线

   fun isAccordWith(str: String): Boolean {
        val pattern = Pattern.compile("^[a-zA-Z0-9_]{4,16}+$")
        val isNum = pattern.matcher(str)
        return if (!isNum.matches()) {
            false
        } else true
    }