我目前正在开发一个Xcode应用程序，允许用户通过向MySQL数据库发送数据进行注册。我只有几个问题。
我遇到的第一个问题是在第10,13,15行。我发出警告说：“字符串插值产生可选值的调试描述;你的意思是明确说明吗？”无论如何我可以更改我的代码，以便该值不是可选的吗？
此外，发送的响应字符串的措辞如下：“responseString = Optional（此用户名可用）”。我打算使用响应字符串向用户显示信息。反正我是否可以摆脱括号以及可选词？
@IBAction func TextFieldEditingDidChange(_ sender: Any) {
let request = NSMutableURLRequest(url: NSURL(string: "usernamecheck.php")! as URL)
request.httpMethod = "POST"
print("Request: \(request)")
let postString = "username=\(usernameTxt.text!)"
request.httpBody = postString.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest) {
data, response, error in
if error != nil {
print("error=\(error)")
return
} // Ends errror If statements
print("response = \(response)")
let responseString = NSString(data: data!, encoding:
String.Encoding.utf8.rawValue)
print("responseString = \(responseString)")
}
task.resume()
}
部分PHP文件：
$a_sql = mysqli_query($con, "SELECT username FROM users WHERE username = '" . mysqli_real_escape_string($_POST['username']) . "' ; ");
if (empty($_POST['username'])) {
$username_error = "Please input username";
} else {
$a_sql;
}
if ($a_sql && mysqli_num_rows($a_sql) > 0) {
$username_exists = "Username is already taken.";
echo $username_exists;
} else {
echo "Fail";
}
答案 0 :(得分：1)
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</nav>这是打开选项的方法之一，但最终取决于你想做什么......
你应该真正阅读Swift中的选项。这是一个非常容易和初学者的话题，每个人都在学习Swift应该学习
答案 1 :(得分：0)
如果让Message = Message { 打印（消息） }
答案 2 :(得分：0)
guard let message = responseString else {
return
}
print(message)
实际上，你正在向消息展开一个可选的响应字符串，现在如果它包含nil，它将不会给出任何异常，它将落入其他情况。 另一方面，该值将存储在消息中并可以进一步使用