如何在ios中永远运行后台服务以同步数据

您好，我正在开发一个应用程序，它需要在网络服务器上进行同步操作（数据提交和检索）。

用户可以离线提交表单（即将数据存储到设备上的本地数据库）。只要网络可用，后台服务就应该将这些数据提交到网络服务器。

后台服务具体需求如下：

• 后台服务会先检查网络是否可用
• 如果网络可用，它将收集本地数据库（SQLite）中的数据存储 在设备上
• 它将数据提交到服务器
• 询问服务器是否有任何新数据，如果有的话，获取该数据 并更新设备上的本地数据库。

我对 iOS 和 xamarin/monotouch 很陌生，想知道如何实现这一点？

我了解iOS中的各种后台模式，例如后台获取、nsurlsession、后台传输等。

我尝试实现后台获取，我认为它适合我的情况。但它按照自己的时间运行。

还想知道如果用户杀死了我的应用程序，那么后台提取也将调用并仍然运行我的应用程序？

我的 appdelegate -> PerformFetch 方法中的代码是这样的：

if(networkService.IsNetworkAvailable())
{
   if(this.syncDataService.DownloadNewDataFromServer())
   {
       Console.WriteLine("Data downloaded successfully from server..");
   }
   if(this.syncDataService.UploadDataToServer())
   {
       Console.WriteLine("Data submitted successfully to server...");
   }
   completionHandler(UIBackgroundFetchResult.NewData);
}
else
{
   completionHandler(UIBackgroundFetchResult.NoData);
}

Update:最后我是这样实现的（希望对某人有帮助）：

public class LocationUpdatedEventArgs : EventArgs
{
    private CLLocation location;

    public LocationUpdatedEventArgs(CLLocation location)
    {
        this.location = location;
    }

    public CLLocation Location
    {
        get { return this.location; }
    }
}

public class LocationManager
    {
        private static DateTime lastServiceRun;

        private CLLocationManager locMgr;

        public LocationManager()
        {
            this.locMgr = new CLLocationManager();
            this.LocationUpdated += this.PrintLocation;
            this.locMgr.Failed += (object sender, NSErrorEventArgs e) =>
            {
                Console.WriteLine("didFailWithError " + e.Error);
                Console.WriteLine("didFailWithError coe " + e.Error.Code);
            };
        }


        public event EventHandler<LocationUpdatedEventArgs> LocationUpdated = delegate { };


        public static TimeSpan TimeDiff { get; set; }


        public CLLocationManager LocMgr
        {
            get
            {
                return this.locMgr;
            }
        }


        public void StartLocationUpdates()
        {

            if (CLLocationManager.LocationServicesEnabled)
            {
                // sets the accuracy that we want in meters
                this.LocMgr.DesiredAccuracy = 1;

                //// Location updates are handled differently pre-iOS 6. If we want to support older versions of iOS,
                //// we want to do perform this check and let our LocationManager know how to handle location updates.

                if (UIDevice.CurrentDevice.CheckSystemVersion(6, 0))
                {
                    this.LocMgr.LocationsUpdated += (object sender, CLLocationsUpdatedEventArgs e) =>
                    {
                        //// fire our custom Location Updated event
                        this.LocationUpdated(this, new LocationUpdatedEventArgs(e.Locations[e.Locations.Length - 1]));
                    };
                }
                else
                {
                    //// this won't be called on iOS 6 (deprecated). We will get a warning here when we build.
                    this.LocMgr.UpdatedLocation += (object sender, CLLocationUpdatedEventArgs e) =>
                    {
                        this.LocationUpdated(this, new LocationUpdatedEventArgs(e.NewLocation));
                    };
                }

                //// Start our location updates
                this.LocMgr.StartUpdatingLocation();

                lastServiceRun = DateTime.Now;

                // Get some output from our manager in case of failure
                this.LocMgr.Failed += (object sender, NSErrorEventArgs e) =>
                {
                    Console.WriteLine(e.Error);
                };
            }
            else
            {
                //// Let the user know that they need to enable LocationServices
                Console.WriteLine("Location services not enabled, please enable this in your Settings");
            }
        }

        /// <summary>
        /// The stop updating location.
        /// </summary>
        public void StopUpdatingLocation()
        {
            this.locMgr.StopUpdatingLocation();
        }

        /// <summary>
        /// The print location. (This will keep going in the background)
        /// </summary>
        /// <param name="sender"> The sender. </param>
        /// <param name="e"> Location updated event argument </param>
        public void PrintLocation(object sender, LocationUpdatedEventArgs e)
        {
            CLLocation location = e.Location;

            Console.WriteLine("Longitude: " + location.Coordinate.Longitude);
            Console.WriteLine("Latitude: " + location.Coordinate.Latitude);

            var diff = DateTime.Now - lastServiceRun;
            TimeDiff = diff;
            if (TimeDiff.Minutes == 2)
            {
        // RunInBackground() is my method which call the service to upload/download data from server
                if (this.RunInBackground())
                {
                    lastServiceRun = DateTime.Now;
                }
            }
        }
}

计时器永远不会在后台工作，并且您不能在此方法中添加另一个线程。DidEnterBackground用于完成待处理的任务。这通常会持续大约 30 秒 - 1 分钟。

您可以在此方法中添加循环或添加长时间运行的任务。