Swift 等待另一个视图控制器的任务完成

Question

I have a Viewcontroller VC_B where I connect to Wifi by using "NEHotspotConfigurationManager.shared" to a special device. This function currently errors because it will return nil whenever success or failure. Please follow these links below. https://developer.apple.com/forums/thread/109412 https://stackoverflow.com/.../nehotspotconfigurationmanag.. .

So I will create a Viewcontroller VC_A, then use "pathUpdateHandler" to catch events whenever the wifi connection changed. Then save wifi SSID to CURENT_SSID by using CoreLocation.

1. access device wifi by DEVICE_SSID at VC_B.
2. wait until CURENT_SSID successfully is updated at VC_A.
3. compare DEVICE_SSID and CURRENT_SSID.

1. VC_A
// get current SSID and save to UserData.shared.current_wifi_ssid
    var ssid: String { 
        var return_ssid:String = "取得できませんでした。"
        if let interfaces = CNCopySupportedInterfaces() as NSArray? {
            for interface in interfaces {
                if let interfaceInfo = CNCopyCurrentNetworkInfo(interface as! CFString) as NSDictionary?,
                    let ssid = interfaceInfo[kCNNetworkInfoKeySSID as String] as? String {
                    return_ssid = ssid
                }
            }
        }
        
        UserData.shared.current_wifi_ssid = return_ssid
        return return_ssid
    }
//catch when having wifi connection changing event
    func checkNetWorking() {
        monitor.pathUpdateHandler = { path in
            if path.status == .satisfied {
                self.isConnected = true
   //check sign in at backend
                Backend.shared.checkSignedIn {(isSignedIn: Bool) in
                    if !isSignedIn {
                        DispatchQueue.main.async {
                            AlertHelper.displayOK(self, title: "エラー", message: "サインインしてください")
                        }
                    }
                }
            } else {
     //the case no internet or already accessed to DEVICE_WIFI           
                //############# location - wifi
            do something
                //#############
            }
        }
    }

2. VC_B
//connect to device wifi and check
    func connectTheta(ID: String){
        TableVIew.isUserInteractionEnabled = false
        SVProgressHUD.show()
        let manager = NEHotspotConfigurationManager.shared
        let ssid = "THETAYN" + ID + ".OSC"
        let password = ID
        let isWEP = false
        let hotspotConfiguration = NEHotspotConfiguration(ssid: ssid, passphrase: password, isWEP: isWEP)
        hotspotConfiguration.joinOnce = true
        hotspotConfiguration.lifeTimeInDays = 1

        UserData.shared.current_wifi_ssid = "NULL"
        manager.apply(hotspotConfiguration) { (error) in //error always nil
            if error != nil {
            // error
          } else {
            // success
          }
            
            check_wifi_theta();
            
            func check_wifi_theta(){
      //i'm using while here to wait task from VC_A (wait until UserData.shared.current_wifi_ssid is updated)
                while(UserData.shared.current_wifi_ssid=="NULL"){
                    Thread.sleep(forTimeInterval: 0.5)
                }
                print("ssid theta", ssid)
                print("ssid current", UserData.shared.current_wifi_ssid)
                if (UserData.shared.current_wifi_ssid==ssid){
                    print("connect Theta OK")
                    AlertHelper.displayOK(self, title: "接続できました", message: "", okHandler: {_ in
                        self.navigationController?.popViewController(animated: true)
                    })
                }
                else{
                    AlertHelper.displayOK(self, title: "接続できません", message: "THETAの電源が入っている確認してください。")
                }
                self.TableVIew.isUserInteractionEnabled = true
                SVProgressHUD.dismiss()
            }
        }
    }

I am stuck at step 2 when trying to wait for "pathUpdateHandler" to finish from VC_B. Sometimes it changes but sometimes it's not. I use while loop here and it's solved my problem. But I think it's is not the best choice. Is there any better solution for this? Thanks!

Answer 1

Firstly, it could be better to clean up yours example code. In your message it is difficult to understand what is going on.

In my opinion it is a bad idea to use infinite while loops in this case. I can advice these options:

1. NSLock

2. Observe event in any way. There are multiple options in iOS, depending on task. You can use delegate pattern and create a delegate protocol and add a reference on VC_B inside VC_A. The similar method is closure usage (save and call closure instead of delegate).

3. Another option is using NotificationCenter to post notifications in VC_A and observe this event in VC_B. It is basic observer pattern usage in iOS, but you can use more advanced techniques like creating your own observer pattern implementation, like multi-delegates observer.