我无法从HTTPrequest返回数据，也无法使完成处理程序正常工作。因此，请协助我解决这个问题：

这是下面的代码：

var dictArr:[String:Any]!

func postaction(_ url:String,completion: @escaping(_ dict:[[String:Any]]) -> Void) {
    guard let serviceUrl = URL(string: url) else { return }

    let parameterDictionary: [String : Any] = [
        "userId": "1","bookingType": "1","pageNumber": "1","filter": ""
    ]

    var request = URLRequest(url: serviceUrl)
    request.httpMethod = "POST"
    print(parameterDictionary)

    let postStr = self.getPostString(params: parameterDictionary)
    let httpBody = postStr.data(using: .utf8)
    request.httpBody = httpBody
    let session = URLSession.shared

    session.dataTask(with: request) { (data,response,error) in
        print("response:--")
        if let response = response {
            print("response:--",response)
        } else if let error = error {
            print("error",error)
        }

        if let data = data {
            do {
                let json = try JSONSerialization.jsonObject(with: data,options: [])
                print(json)
                self.dictArr = json as! [[String:Any]]
                completion(self.dictArr)
            } catch {
                print(error)
            }
        }
    }.resume()
}

func getPostString(params: [String : Any]) -> String {
    var data = [String]()
    for(key,value) in params{
        data.append(key + "=\(value)")
    }
    return data.map { String($0) }.joined(separator: "&")
}

请尽快回复。