iOS请求接口JSON序列化失败，提示格式不正确问题排查

问题根源与修复步骤 #

1. 缺失Content-Type请求头

你的POST请求未声明请求体格式，服务器可能无法正确解析参数，返回非JSON内容（比如错误页面），导致解析失败。需添加：

request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")

2. 强制解包data!存在风险

即使error为nil，data也可能为空或非JSON数据。先判断数据有效性：

guard let data = data else {
    print("无返回数据")
    return
}

3. 避免使用NSMutableDictionary，改用Swift原生类型

Swift中推荐用[String: Any]替代OC的可变字典，类型更安全：

if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
    if let id = json["id"] as? String {
        print(id)
    }
}

4. 手动拼接参数易出错，改用URLComponents编码

手动拼接的参数若包含特殊字符（如空格、@），会导致请求体格式错误，服务器无法处理。用URLComponents自动编码：

let bodyComponents = URLComponents()
bodyComponents.queryItems = [
    URLQueryItem(name: "username", value: usernameTxt.text?.lowercased() ?? ""),
    URLQueryItem(name: "password", value: passwordTXT.text ?? ""),
    URLQueryItem(name: "email", value: emailTxt.text ?? ""),
    URLQueryItem(name: "fullname", value: "\(nameTxt.text ?? "") \(surnameTxt.text ?? "")")
]
request.httpBody = bodyComponents.query?.data(using: .utf8)

完整修复代码 #

guard let url = URL(string: "http://localhost/DataDog/registering.php") else {
    return
}

var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")

// 构建编码后的请求体
let bodyComponents = URLComponents()
bodyComponents.queryItems = [
    URLQueryItem(name: "username", value: usernameTxt.text?.lowercased() ?? ""),
    URLQueryItem(name: "password", value: passwordTXT.text ?? ""),
    URLQueryItem(name: "email", value: emailTxt.text ?? ""),
    URLQueryItem(name: "fullname", value: "\(nameTxt.text ?? "") \(surnameTxt.text ?? "")")
]
request.httpBody = bodyComponents.query?.data(using: .utf8)

URLSession.shared.dataTask(with: request) { data, response, error in
    if let error = error {
        print("请求错误：\(error.localizedDescription)")
        return
    }
    
    guard let data = data else {
        print("无返回数据")
        return
    }
    
    // 打印原始返回内容，排查是否为纯JSON
    if let responseString = String(data: data, encoding: .utf8) {
        print("服务器返回：\(responseString)")
    }
    
    DispatchQueue.main.async {
        do {
            if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
                if let id = json["id"] as? String {
                    print("用户ID：\(id)")
                }
                // 可扩展处理其他字段
                if let status = json["status"] as? String {
                    print("状态码：\(status)")
                }
            }
        } catch let error as NSError {
            print("JSON解析失败：\(error.localizedDescription)")
        }
    }
}.resume()

内容的提问来源于stack exchange，提问作者Michael Drammond