ios - 等待 session.dataTask 上的任务返回

Question

我有一个项目，我通过 API 发送和获取数据。发送和获取工作正常。

我的目标是等待服务器的响应(即:是|否)，并根据它，是否继续继续，如果否则显示警报。

对于这部分我有:

1. 带有客户端列表和添加新客户端的按钮的表格 View 。
2. 我在其中添加/编辑客户的详细 View
3. 在详细信息 View 上有一个保存按钮，可连接到表格 View

函数saveClient()获取数据并向服务器发出请求

func saveClient() -> Bool {

    let name = txtName.text ?? ""
    let address = txtAddress.text ?? ""
    let city = txtCity.text ?? ""
    let province = txtProvince.text ?? ""
    let postal_code = txtPostalCode.text ?? ""

    meal = Client(name:name, client_id: "", postal_code: postal_code, province: province, city: city, address: address)

    var jsonData = Data()
    let jsonEncoder = JSONEncoder()
    do {
        jsonData = try jsonEncoder.encode(meal)
    }
    catch {
    }
    print("a1")
    var success: Bool
    success = false

    makeRequestPost(endpoint: "http://blog.local:4711/api/clients/add",
                    requestType: "POST",
                    requestBody: jsonData,
                    completionHandler: { (response : ApiContainer<Client>?, error : Error?) in
                        if let error = error {
                            print("error calling POST on /todos")
                            print(error)
                            return
                        }
                        let b = (response?.meta)!
                        print(b.sucess)
                        if(b.sucess == "yes") {
                            success = true
                        }
                        else
                        {
                            DispatchQueue.main.async(execute: {
                                let myAlert = UIAlertController(title: "Error", message: "Error creating Client", preferredStyle: .alert)
                                let okAction = UIAlertAction(title: "Ok", style: .default, handler: nil)
                                myAlert.addAction(okAction)
                                self.present(myAlert, animated: true, completion: nil)
                            })
                            return
                        }
    } )
    return success
}

在同一个 Controller 上:

override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {

    guard let button = sender as? UIBarButtonItem, button === btnSave else {
        return false
    }

    if !saveClient() {
        print("no sir")
        return false
    }

    print("yes sir")
    return true
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    super.prepare(for: segue, sender: sender)        
    guard let button = sender as? UIBarButtonItem, button === btnSave else {
        return
    }
}

请求函数:

func makeRequestPost<T>(endpoint: String,
                     requestType: String = "GET",
                     requestBody: Data,  completionHandler: @escaping (ApiContainer<T>?, Error?) -> ()) {

    guard let url = URL(string: endpoint) else {
        print("Error: cannot create URL")
        let error = BackendError.urlError(reason: "Could not create URL")
        completionHandler(nil, error)
        return
    }

    var urlRequest = URLRequest(url: url)
    let session = URLSession.shared

    urlRequest.httpMethod = "POST"
    urlRequest.httpBody = requestBody

    urlRequest.addValue("application/json", forHTTPHeaderField: "Content-Type")
    urlRequest.addValue("application/json", forHTTPHeaderField: "Accept")



    let task = session.dataTask(with: urlRequest, completionHandler: {
        (data, response, error) in
        guard let responseData = data else {
            print("Error: did not receive data")
            completionHandler(nil, error)
            return
        }
        guard error == nil else {
            completionHandler(nil, error!)
            return
        }

        do {
            let response = try JSONDecoder().decode(ApiContainer<T>.self, from: responseData)
            completionHandler(response, nil)
        }
        catch {
            print("error trying to convert data to JSON")
            print(error)
            completionHandler(nil, error)
        }

    })
    task.resume()
}

在控制台上我得到:

a1

no sir

yes

正确的是:

a1

yes

yes sir

最后的注释:

1. 我尝试了一些带有信号量的示例...但没有成功。

2. 我在其他地方使用名为 Meal 的 var，但尚未将其更改为客户端。但是，它不会干扰那部分代码

Answer 1

你说:

My goal is to wait a response (ie: yes|no) from the server and depending on it, proceed with the segue or not

虽然我理解这种方法的自然吸引力，但现实是您永远不应该“等待”(尤其是在 shouldPerformSegue 中)。您的 UI 将卡住(如果用户的互联网连接较差，则尤其值得注意)，您的应用程序很容易被寻找卡住应用程序的看门狗进程杀死，等等。

因此，不要执行segue并让shouldPerformSegue尝试等待网络响应以查看是否可以继续，而是以相反的方式进行:您可以编写执行查询的代码如果一切正常，则只能以编程方式启动 segue。