在swift singleton中调用异步函数的正确方法

Question

我想为我的应用程序构建一个分析类，并且我正在使用单例。

如果我运行这个，tagEvent函数立即运行而不是首先运行openSession（），所以sessionId返回nil。 如何通过适当的初始化创建一个像这样的类，并像单例实例一样使用它。

Analytics.swift

final class Analytics { 
    public static let instance = Analytics() 
    private var baseUrl = "http://localhost" 
    public var deviceId: String? 

    private init(){ 
     self.deviceId = SomeFunctionGetsDeviceID() 
    } 

    func openSession(){ 
     // make an API call to create a session and save sessionId to UserDefaults 
     if let url = URL(string: self.baseUrl + "/session"){ 
      let params:[String:Any] = ["deviceId": "\(self.deviceId!)"] 

      var request = URLRequest(url: url) 
      request.setValue("application/json", forHTTPHeaderField:"Content-Type") 
      request.httpMethod = "POST" 
      request.httpBody = try! JSONSerialization.data(withJSONObject: params, options: []) 

      AnalyticsSessionManager.sharedManager.request(request as URLRequestConvertible).validate().responseObject(completionHandler: { (response: DataResponse<SessionOpenResponse>) in 
       if response.result.value != nil { 
        UserDefaults.standard.set(response.result.value?.sessionId, forKey: "sessionId") 
       } 
      }) 
     } 
    } 

    func closeSession(){ 
     // make an API call to close a session and delete sessionId from UserDefaults 
    ... 
    } 

    func tagEvent(eventName: String, attributes: [String : String]? = nil) { 
     if let url = URL(string: self.baseUrl + "/event"), 
      let sessionId = UserDefaults.standard.string(forKey: "sessionId"){ 
      ... 
      // make an API call to create an event with that sessionId 
     } 
    } 
} 

AppDelegate.swift

func application(_ application: UIApplication, 
    didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool { 
    Analytics.instance.openSession() 
    Analytics.instance.tagEvent(eventName: "App Launch", attributes: 
    ["userID":"1234"]) 
} 

Answer 1

我最好的猜测是的openSession功能是异步做功和tagEvent电话打进来之前，异步代码有完成。有几种解决方法：

1）添加同步，以便tagEvent代码将等待openSession调用完成（如果正在进行中）。如果不是在进步，也许它会自动调用openSession时，等待完成，然后在功能

2）执行代码的openSession添加完成处理程序和机箱内部可以调用tagEvent如：

func openSession(completionHandler: @escapaing (Bool) ->()){ 
    // make an API call to create a session and save sessionId to UserDefaults 
    ... 
    UserDefaults.standard.set(someSessionID, forKey: "sessionId") 

    // when done with async work 
    completionHandler(true) 
} 

然后在您的应用程序代理：

Analytics.instance.openSession() { (success) 
    Analytics.instance.tagEvent(eventName: "App Launch", attributes:["userID":"1234"]) 
} 

3）*这是我会修*我不会让类以外的地方需要的openSession呼叫的方式。我想一个标志添加到Analytics（分析）类：

private var initialized = false 

在的openSession功能，设置这一切都做

initialized = true 

后在tagEvent功能：

func tagEvent(eventName: String, attributes: [String : String]? = nil) { 
    // Check for initialization 
    if (!initialized) { 
     openSession() { (success) in 
      // perform your tagEvent code 
     }) 
    } else { 
     if let url = URL(string: self.baseUrl + "/event"), 
      let sessionId = UserDefaults.standard.string(forKey: "sessionId"){ 
      ... 
      // make an API call to create an event with that sessionId 
     } 
    } 
} 

Answer 2

您可以实现一个“内部”类，为您的Analytics类提供静态参考，如下所示（注意：删除final关键字）：

从任何其他类的分析类

class Analytics { 

// properties ... 

    class var sharedInstance: Analytics { 
     struct Static { 
      static let instance: Analytics = Analytics() 
     } 
     return Static.instance 
    } 

// other methods (init(), openSession(), closeSession(), tagEvent()) 

} 

接下来调用方法如下：

Analytics.sharedInstance.openSession() 
Analytics.sharedInstance.closeSession() 
Analytics.sharedInstance.tagEvent(...)