当NSUrlSession充电器电缆拔出在iOS 14.4上时，BGTaskScheduler内部的iOS照片上传任务不会执行

Question

我们正在开发一个Xamarin Forms应用程序，它应该在后台将照片上传到API。该应用程序是根据客户的要求为客户定制的，因此他们会将手机设置为任何需要设置的权限。

如果充电电缆插上电源，下面就可以正常工作了。

我正在使用BGTaskScheduler (iOS13+)并对这两种类型的任务(BGProcessingTaskRequest和BGAppRefreshTaskRequest)进行排队，这样如果插入电缆就会触发BGProcessingTaskRequest，如果没有，则等待BGAppRefreshTaskRequest获得处理时间。

我将RefreshTaskId和UploadTaskId添加到Info.plist中

AppDelegate.cs in iOS项目如下

  public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        global::Xamarin.Forms.Forms.Init();
        LoadApplication(new App());

        BGTaskScheduler.Shared.Register(UploadTaskId, null, task => HandleUpload(task as BGProcessingTask));
        BGTaskScheduler.Shared.Register(RefreshTaskId, null, task => HandleAppRefresh(task as BGAppRefreshTask));

        return base.FinishedLaunching(app, options);
    }

    public override void HandleEventsForBackgroundUrl(UIApplication application, string sessionIdentifier, Action completionHandler)
    {
        Console.WriteLine("HandleEventsForBackgroundUrl");
        BackgroundSessionCompletionHandler = completionHandler;
    }
    public override void OnActivated(UIApplication application)
    {
        Console.WriteLine("OnActivated");
    }

    public override void OnResignActivation(UIApplication application)
    {
        Console.WriteLine("OnResignActivation");
    }

    private void HandleAppRefresh(BGAppRefreshTask task)
    {
        HandleUpload(task);
    }

    public override void DidEnterBackground(UIApplication application)
    {
        ScheduleUpload();
    }

    private void HandleUpload(BGTask task)
    {
        var uploadService = new UploadService();
        uploadService.EnqueueUpload();
        task.SetTaskCompleted(true);
    }

    private void ScheduleUpload()
    {
        var upload = new BGProcessingTaskRequest(UploadTaskId)
        {
            RequiresNetworkConnectivity = true,
            RequiresExternalPower = false
        };

        BGTaskScheduler.Shared.Submit(upload, out NSError error);

        var refresh = new BGAppRefreshTaskRequest(RefreshTaskId);

        BGTaskScheduler.Shared.Submit(refresh, out NSError refreshError);

        if (error != null)
            Console.WriteLine($"Could not schedule BGProcessingTask: {error}");
        if (refreshError != null)
            Console.WriteLine($"Could not schedule BGAppRefreshTask: {refreshError}");
    }

上传UploadService的机制是使用NSUrlSession，它还编写了一个临时文件来使用应该在后台工作的CreateUploadTask(request, NSUrl.FromFilename(tempFileName))，整个机制如下：

 public NSUrlSession uploadSession;

    public async void EnqueueUpload()
    {
        var accountsTask = await App.PCA.GetAccountsAsync();
        var authResult = await App.PCA.AcquireTokenSilent(App.Scopes, accountsTask.First())
                                      .ExecuteAsync();

        if (uploadSession == null)
            uploadSession = InitBackgroundSession(authResult.AccessToken);

        var datastore = DependencyService.Get<IDataStore<Upload>>();
        var uploads = await datastore.GetUnuploaded();

        foreach (var unUploaded in uploads)
        {
            try
            {
                string folder = unUploaded.Description;
                string subfolder = unUploaded.Category;

                if (string.IsNullOrEmpty(folder) || string.IsNullOrEmpty(subfolder))
                    continue;

                var uploadDto = new Dtos.Upload
                {
                    FolderName = folder,
                    SubFolderName = subfolder,
                    Image = GetImageAsBase64(unUploaded.ImagePath)
                };
                var documents = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
                var fileName = Path.GetFileName(unUploaded.ImagePath);
                var tempFileName = Path.Combine(documents, $"{fileName}.txt");
                string stringContent = await new StringContent(JsonConvert.SerializeObject(uploadDto), Encoding.UTF8, "application/json").ReadAsStringAsync();
                await File.WriteAllTextAsync(tempFileName, stringContent);

                using (var url = NSUrl.FromString(UploadUrlString))
                using (var request = new NSMutableUrlRequest(url)
                {
                    HttpMethod = "POST",

                })
                {
                    request.Headers.SetValueForKey(NSObject.FromObject("application/json"), new NSString("Content-type"));
                    try
                    {
                        uploadSession.CreateUploadTask(request, NSUrl.FromFilename(tempFileName));

                    }
                    catch (Exception e)
                    {
                        Console.WriteLine($"NSMutableUrlRequest failed {e.Message}");
                    }
                }
            }
            catch (Exception e)
            {
                if (e.Message.Contains("Could not find a part of the path"))
                {
                    await datastore.DeleteItemAsync(unUploaded.Id);
                    Console.WriteLine($"deleted");
                }

                Console.WriteLine($"uploadStore failed {e.Message}");
            }
        }
    }
    private string GetImageAsBase64(string path)
    {
        using (var reader = new StreamReader(path))
        using (MemoryStream ms = new MemoryStream())
        {
            reader.BaseStream.CopyTo(ms);
            return Convert.ToBase64String(ms.ToArray());
        }
    }

    public NSUrlSession InitBackgroundSession(string authToken = null, IDataStore<Upload> dataStore = null)
    {
        Console.WriteLine("InitBackgroundSession");
        using (var configuration = NSUrlSessionConfiguration.CreateBackgroundSessionConfiguration(Identifier))
        {
            configuration.AllowsCellularAccess = true;
            configuration.Discretionary = false;
            configuration.AllowsConstrainedNetworkAccess = true;
            configuration.AllowsExpensiveNetworkAccess = true;
            if (string.IsNullOrWhiteSpace(authToken) == false)
            {
                configuration.HttpAdditionalHeaders = NSDictionary.FromObjectsAndKeys(new string[] { $"Bearer {authToken}" }, new string[] { "Authorization" });
            }

            return NSUrlSession.FromConfiguration(configuration, new UploadDelegate(dataStore), null);
        }
    }
}

public class UploadDelegate : NSUrlSessionTaskDelegate, INSUrlSessionDelegate
{
    public IDataStore<Upload> Datastore { get; }

    public UploadDelegate(IDataStore<Upload> datastore)
    {
        this.Datastore = datastore;
    }
    public override void DidCompleteWithError(NSUrlSession session, NSUrlSessionTask task, NSError error)
    {
        Console.WriteLine(string.Format("DidCompleteWithError TaskId: {0}{1}", task.TaskIdentifier, (error == null ? "" : " Error: " + error.Description)));

        if (error == null)
        {
            ProcessCompletedTask(task);
        }
    }
    public void ProcessCompletedTask(NSUrlSessionTask sessionTask)
    {
        try
        {
            Console.WriteLine(string.Format("Task ID: {0}, State: {1}, Response: {2}", sessionTask.TaskIdentifier, sessionTask.State, sessionTask.Response));

            if (sessionTask.Response == null || sessionTask.Response.ToString() == "")
            {
                Console.WriteLine("ProcessCompletedTask no response...");
            }
            else
            {
                var resp = (NSHttpUrlResponse)sessionTask.Response;
                Console.WriteLine("ProcessCompletedTask got response...");
                if (sessionTask.State == NSUrlSessionTaskState.Completed && resp.StatusCode == 201)
                {
                    Console.WriteLine("201");
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("ProcessCompletedTask Ex: {0}", ex.Message);
        }
    }
    public override void DidBecomeInvalid(NSUrlSession session, NSError error)
    {
        Console.WriteLine("DidBecomeInvalid" + (error == null ? "undefined" : error.Description));
    }

    public override void DidFinishEventsForBackgroundSession(NSUrlSession session)
    {
        Console.WriteLine("DidFinishEventsForBackgroundSession");
    }
    public override void DidSendBodyData(NSUrlSession session, NSUrlSessionTask task, long bytesSent, long totalBytesSent, long totalBytesExpectedToSend)
    {
    }
}

但是，如果iOS充电器电缆插上电源，一切都会正常工作。我设置了一个网络调试，大量登录到控制台，我可以看到iPhone上什么也没有发生。

iOS上的“低功耗模式”设置是关闭的。

我看过背景执行神秘性，正在设置configuration.Discretionary = false;会话

在NSUrlSession 14.4?上拔出iOS充电器电缆时，如何使上传任务启动

Answer 1

下列工程无需充电电缆：

public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
   
    public Action BackgroundSessionCompletionHandler { get; set; }

    public static string UploadTaskId { get; } = "XXX.upload";
    public static NSString UploadSuccessNotificationName { get; } = new NSString($"{UploadTaskId}.success");
    public static string RefreshTaskId { get; } = "XXX.refresh";
    public static NSString RefreshSuccessNotificationName { get; } = new NSString($"{RefreshTaskId}.success");

    public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        global::Xamarin.Forms.Forms.Init();
        LoadApplication(new App());

        BGTaskScheduler.Shared.Register(UploadTaskId, null, task => HandleUpload(task as BGProcessingTask));
        BGTaskScheduler.Shared.Register(RefreshTaskId, null, task => HandleAppRefresh(task as BGAppRefreshTask));

        return base.FinishedLaunching(app, options);
    }

    public override bool OpenUrl(UIApplication app, NSUrl url, NSDictionary options)
    {
        AuthenticationContinuationHelper.SetAuthenticationContinuationEventArgs(url);
        return true;
    }

    public override void HandleEventsForBackgroundUrl(UIApplication application, string sessionIdentifier, Action completionHandler)
    {
        Console.WriteLine("HandleEventsForBackgroundUrl");
        BackgroundSessionCompletionHandler = completionHandler;
    }

    public override void OnActivated(UIApplication application)
    {
        Console.WriteLine("OnActivated");
        var uploadService = new UploadService();
        uploadService.EnqueueUpload();
    }

    public override void OnResignActivation(UIApplication application)
    {
        Console.WriteLine("OnResignActivation");
    }

    private void HandleAppRefresh(BGAppRefreshTask task)
    {
        task.ExpirationHandler = () =>
        {
            Console.WriteLine("BGAppRefreshTask ExpirationHandler");

            var refresh = new BGAppRefreshTaskRequest(RefreshTaskId);
            BGTaskScheduler.Shared.Submit(refresh, out NSError refreshError);

            if (refreshError != null)
                Console.WriteLine($"BGAppRefreshTask ExpirationHandler Could not schedule BGAppRefreshTask: {refreshError}");
        };

        HandleUpload(task);
    }

    public override void DidEnterBackground(UIApplication application) => ScheduleUpload();

    private void HandleUpload(BGTask task)
    {
        Console.WriteLine("HandleUpload");
        var uploadService = new UploadService();
        uploadService.EnqueueUpload();
        task.SetTaskCompleted(true);
    }

    private void ScheduleUpload()
    {
        Console.WriteLine("ScheduleUpload");
        var upload = new BGProcessingTaskRequest(UploadTaskId)
        {
            RequiresNetworkConnectivity = true,
            RequiresExternalPower = false
        };

        BGTaskScheduler.Shared.Submit(upload, out NSError error);

        var refresh = new BGAppRefreshTaskRequest(RefreshTaskId);
        BGTaskScheduler.Shared.Submit(refresh, out NSError refreshError);

        if (error != null)
            Console.WriteLine($"Could not schedule BGProcessingTask: {error}");
        if (refreshError != null)
            Console.WriteLine($"Could not schedule BGAppRefreshTask: {refreshError}");
    }
}

然后上传服务：

public class UploadService : IUploadService
{
    private const string uploadUrlString = "https://Yadyyadyyada";

    public async void EnqueueUpload()
    {
        var accountsTask = await App.PCA.GetAccountsAsync();
        var authResult = await App.PCA.AcquireTokenSilent(App.Scopes, accountsTask.First())
                                      .ExecuteAsync();

                try
                {
                    var uploadDto = new object();

                    var message = new HttpRequestMessage(HttpMethod.Post, uploadUrlString);
                    message.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", authResult.AccessToken);
                    message.Content = new StringContent(JsonConvert.SerializeObject(uploadDto), Encoding.UTF8, "application/json");

                    var response = await httpClient.SendAsync(message);
                    if (response.IsSuccessStatusCode)
                    {
                        var json = await response.Content.ReadAsStringAsync();
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine($"EnqueueUpload {e.Message}");
                }
    }
}