Alamofire POST请求报错：如何将Foundation.URLRequest转为URLConvertible？

问题场景 #

尝试使用Alamofire发送带JSON请求体的POST请求时，运行报错：

Could not cast value of type 'Foundation.URLRequest' to 'Alamofire.URLConvertible'

原请求代码如下：

let credential = URLCredential(user: appDelegate.username!, password: appDelegate.password!, persistence: .none)
        
var url = URL(string: webservice)
        
var request = URLRequest(url: url!)

request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.httpMethod = "POST"
request.httpBody = jsonData

let urlRequest: Alamofire.URLRequestConvertible = request

AF.request(urlRequest as! URLConvertible, headers: headers).authenticate(with: credential).response { response in
    
}

核心解决方法 #

Foundation.URLRequest本身已经遵循了Alamofire的URLRequestConvertible协议，不需要任何强制转换，直接将构建好的request传入AF.request即可。修改后的请求代码如下：

let credential = URLCredential(user: appDelegate.username!, password: appDelegate.password!, persistence: .none)
        
guard let url = URL(string: webservice) else {
    // 处理URL初始化失败的情况
    return
}
        
var request = URLRequest(url: url)

request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.httpMethod = "POST"
request.httpBody = jsonData

// 直接传入request，无需强制转换
AF.request(request, headers: headers).authenticate(with: credential).response { response in
    // 处理响应
}

额外代码问题修复 #

除了转换错误，你的代码还有几个潜在问题需要修正：

• MyClass初始化方法类型不匹配
  类中notes属性是String?，但初始化方法的notes参数是Int?，类型不一致，修改为：

  class MyClass: NSObject {
      var id: Int?
      var item: String?
      var notes: String?
      
      init(id: Int?, item: String?, notes: String?) {
          super.init()
          self.id = id
          self.item = item
          self.notes = notes
      }
  }
  

• JSON数据处理的可选值安全
  jsonData是可选类型，直接赋值给httpBody可能导致请求体为空，建议添加错误处理：

  do {
      let jsonData = try JSONSerialization.data(withJSONObject: jsonArrayOfDictionaries, options: .prettyPrinted)
      request.httpBody = jsonData
  } catch {
      print("JSON序列化失败：\(error)")
      return
  }
  

• 循环中冗余的字典初始化
  循环内无需重复执行jsonDict = [AnyHashable: Any]()，因为每次循环开头已经通过var jsonDict = [AnyHashable: Any]()创建了新字典：

  var jsonArrayOfDictionaries = [[AnyHashable: Any]]()
  for item in cellHolder {
      var jsonDict = [AnyHashable: Any]()
      jsonDict["ID"] = item.id
      jsonDict["item"] = item.item
      jsonDict["Notes"] = item.notes
      jsonArrayOfDictionaries.append(jsonDict)
  }
  

内容的提问来源于stack exchange，提问作者user979331