从 TimerCallback 实例调用时，调用 Dropbox API Client.Files.DownloadAsync 不会 return 元数据
Call to Dropbox API Client.Files.DownloadAsync does not return metadata when call from an instance of TimerCallback
我有一个移动跨平台 Xamarin.Forms 项目，我在其中尝试在启动时从 Dropbox 存储库下载文件。这是一个小于 50kB 的 json 文件。操作 Dropbox API 调用的代码在我的 Android 和我的 iOS 项目之间共享，并且我的 Android 实现按预期工作。这是一个 Task 方法，为了方便起见，我在这里将其称为 downloader。
更新： 使用 iOS 版本，我只能在调用 downloader 的启动器（这也是一个任务）时才能成功下载文件) 直接来自我唯一的 AppDelegate 的 BackgroundSynchronizer.Launch() 方法，但在使用计时器委托此调用通过调用 EventHandler 调用我的 downloader 时则不会] 重复出现。
我不明白为什么。
downloader：
public class DropboxStorage : IDistantStoreService
{
private string oAuthToken;
private DropboxClientConfig clientConfig;
private Logger logger = new Logger
(DependencyService.Get<ILoggingBackend>());
public DropboxStorage()
{
var httpClient = new HttpClient(new NativeMessageHandler());
clientConfig = new DropboxClientConfig
{
HttpClient = httpClient
};
}
public async Task SetConnection()
{
await GetAccessToken();
}
public async Task<Stream> DownloadFile(string distantUri)
{
logger.Info("Dropbox downloader called.");
try
{
await SetConnection();
using var client = new DropboxClient(oAuthToken, clientConfig);
var downloadArg = new DownloadArg(distantUri);
var metadata = await client.Files.DownloadAsync(downloadArg);
var stream = metadata?.GetContentAsStreamAsync();
return await stream;
}
catch (Exception ex)
{
logger.Error(ex);
}
return null;
}
更新： AppDelegate：
using Foundation;
using UIKit;
namespace Izibio.iOS
{
// The UIApplicationDelegate for the application. This class is responsible for launching the
// User Interface of the application, as well as listening (and optionally responding) to
// application events from iOS.
[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
private BackgroundSynchronizer synchronizer = new BackgroundSynchronizer();
//
// This method is invoked when the application has loaded and is ready to run. In this
// method you should instantiate the window, load the UI into it and then make the window
// visible.
//
// You have 17 seconds to return from this method, or iOS will terminate your application.
//
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init();
LoadApplication(new App());
return base.FinishedLaunching(app, options);
}
public override void OnActivated(UIApplication uiApplication)
{
synchronizer.Launch();
base.OnActivated(uiApplication);
}
}
}
编辑： 中介 class（嵌入了 DownloadProducts 功能）：
public static class DropboxNetworkRequests
{
public static async Task DownloadProducts(IDistantStoreService distantStorage,
IStoreService localStorage)
{
try
{
var productsFileName = Path.GetFileName(Globals.ProductsFile);
var storeDirectory = $"/{Globals.StoreId}_products";
var productsFileUri = Path.Combine(storeDirectory, productsFileName);
var stream = await distantStorage.DownloadFile(productsFileUri);
if (stream != null)
{
await localStorage.Save(stream, productsFileUri);
}
else
{
var logger = GetLogger();
logger.Info($"No file with the uri ’{productsFileUri}’ could " +
$"have been downloaded.");
}
}
catch (Exception ex)
{
var logger = GetLogger();
logger.Error(ex);
}
}
private static Logger GetLogger()
{
var loggingBackend = DependencyService.Get<ILoggingBackend>();
return new Logger(loggingBackend);
}
}
更新： 和失败的启动器 class（Launch 方法中注释的 TriggerNetworkOperations(this, EventArgs.Empty);
成功下载文件）：
public class BackgroundSynchronizer
{
private bool isDownloadRunning;
private IDistantStoreService distantStorage;
private IStoreService localStorage;
private Timer timer;
public event EventHandler SynchronizationRequested;
public BackgroundSynchronizer()
{
Forms.Init();
isDownloadRunning = false;
distantStorage = DependencyService.Get<IDistantStoreService>();
localStorage = DependencyService.Get<IStoreService>();
Connectivity.ConnectivityChanged += TriggerNetworkOperations;
SynchronizationRequested += TriggerNetworkOperations;
}
public void Launch()
{
try
{
var millisecondsInterval = Globals.AutoDownloadMillisecondsInterval;
var callback = new TimerCallback(SynchronizationCallback);
timer = new Timer(callback, this, 0, 0);
timer.Change(0, millisecondsInterval);
//TriggerNetworkOperations(this, EventArgs.Empty);
}
catch (Exception ex)
{
throw ex;
}
}
protected virtual void OnSynchronizationRequested(object sender, EventArgs e)
{
SynchronizationRequested?.Invoke(sender, e);
}
private async void TriggerNetworkOperations(object sender, ConnectivityChangedEventArgs e)
{
if ((e.NetworkAccess == NetworkAccess.Internet) && !isDownloadRunning)
{
await DownloadProducts(sender);
}
}
private async void TriggerNetworkOperations(object sender, EventArgs e)
{
if (!isDownloadRunning)
{
await DownloadProducts(sender);
}
}
private void SynchronizationCallback(object state)
{
SynchronizationRequested(state, EventArgs.Empty);
}
private async Task DownloadProducts(object sender)
{
var instance = (BackgroundSynchronizer)sender;
//Anti-reentrance assignments commented for debugging purposes
//isDownloadRunning = true;
await DropboxNetworkRequests.DownloadProducts(instance.distantStorage, instance.localStorage);
//isDownloadRunning = false;
}
}
我设置了一个日志文件来记录我尝试下载时的应用程序行为。
编辑： 以下是我从 Launch 方法直接调用 TriggerNetworkOperations 时收到的消息：
2019-11-12 19:31:57.1758|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-12 19:31:57.4875|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:31:58.4810|INFO|persistenceLogger|Writing /MAZEDI_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/5BABB56B-9B42-4653-9D3E-3C60CFFD50A8/data/Containers/Data/Application/D6C517E9-3446-4916-AD8D-565F4C206AF2/Library/assortiment.json
编辑： 是我在通过计时器及其回调启动时得到的（用于调试的间隔为 10 秒）：
2019-11-12 19:34:05.5166|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-12 19:34:05.8149|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:15.8083|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:25.8087|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:35.8089|INFO|persistenceLogger|Dropbox downloader called.
编辑： 在第二种情况下，启动的任务事件最终被 OS:
取消
2019-11-13 09:36:29.7359|ERROR|persistenceLogger|System.Threading.Tasks.TaskCanceledException: A task was canceled.
at ModernHttpClient.NativeMessageHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x002a5] in /Users/paul/code/paulcbetts/modernhttpclient/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs:139
at System.Net.Http.HttpClient.SendAsyncWorker (System.Net.Http.HttpRequestMessage request, System.Net.Http.HttpCompletionOption completionOption, System.Threading.CancellationToken cancellationToken) [0x0009e] in /Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/external/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:281
at Dropbox.Api.DropboxRequestHandler.RequestJsonString (System.String host, System.String routeName, System.String auth, Dropbox.Api.DropboxRequestHandler+RouteStyle routeStyle, System.String requestArg, System.IO.Stream body) [0x0030f] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Dropbox.Api.DropboxRequestHandler.RequestJsonStringWithRetry (System.String host, System.String routeName, System.String auth, Dropbox.Api.DropboxRequestHandler+RouteStyle routeStyle, System.String requestArg, System.IO.Stream body) [0x000f6] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Dropbox.Api.DropboxRequestHandler.Dropbox.Api.Stone.ITransport.SendDownloadRequestAsync[TRequest,TResponse,TError] (TRequest request, System.String host, System.String route, System.String auth, Dropbox.Api.Stone.IEncoder`1[T] requestEncoder, Dropbox.Api.Stone.IDecoder`1[T] resposneDecoder, Dropbox.Api.Stone.IDecoder`1[T] errorDecoder) [0x000a5] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Izibio.Persistence.DropboxStorage.DownloadFile (System.String distantUri) [0x00105] in /Users/dev3/Virtual Machines.localized/shared/TRACAVRAC/izibio-mobile/Izibio/Izibio.Persistence/Services/DropboxStorage.cs:44
2019-11-13 09:36:29.7399|INFO|persistenceLogger|No file with the uri ’/******_products/assortiment.json’ could have been downloaded.
我将简单地添加最后一个观察结果：当从 BackgroundSynchronizer 调试 DownloadFile 任务时，我可以到达对 client.Files.DowloadAsync 的调用：var metadata = await client.Files.DownloadAsync(downloadArg);，但是我不会从此等待语句中检索任何 return。
好的，我终于找到了解决这个问题的方法，方法是用 iOS 实现 (NSTimer) 替换 .NET 计时器。
我的 BackgroundSynchronizer 新代码 class：
public class BackgroundSynchronizer
{
private bool isDownloadRunning;
private IDistantStoreService distantStorage;
private IStoreService localStorage;
private NSTimer timer;
public event EventHandler SynchronizationRequested;
public BackgroundSynchronizer()
{
Forms.Init();
isDownloadRunning = false;
distantStorage = DependencyService.Get<IDistantStoreService>();
localStorage = DependencyService.Get<IStoreService>();
Connectivity.ConnectivityChanged += TriggerNetworkOperations;
SynchronizationRequested += TriggerNetworkOperations;
}
public void Launch()
{
try
{
var seconds = Globals.AutoDownloadMillisecondsInterval / 1000;
var interval = new TimeSpan(0, 0, seconds);
var callback = new Action<NSTimer>(SynchronizationCallback);
StartTimer(interval, callback);
}
catch (Exception ex)
{
throw ex;
}
}
protected virtual void OnSynchronizationRequested(object sender, EventArgs e)
{
SynchronizationRequested?.Invoke(sender, e);
}
private async void TriggerNetworkOperations(object sender, ConnectivityChangedEventArgs e)
{
if ((e.NetworkAccess == NetworkAccess.Internet) && !isDownloadRunning)
{
await DownloadProducts();
}
}
private async void TriggerNetworkOperations(object sender, EventArgs e)
{
if (!isDownloadRunning)
{
await DownloadProducts();
}
}
private void SynchronizationCallback(object state)
{
SynchronizationRequested(state, EventArgs.Empty);
}
private async Task DownloadProducts()
{
isDownloadRunning = true;
await DropboxNetworkRequests.DownloadProducts(distantStorage, localStorage);
isDownloadRunning = false;
}
private void StartTimer(TimeSpan interval, Action<NSTimer> callback)
{
timer = NSTimer.CreateRepeatingTimer(interval, callback);
NSRunLoop.Main.AddTimer(timer, NSRunLoopMode.Common);
}
}
产生以下日志行：
2019-11-13 14:00:58.2086|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-13 14:01:08.5378|INFO|persistenceLogger|Dropbox downloader called.
2019-11-13 14:01:09.5656|INFO|persistenceLogger|Writing /****_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/****/data/Containers/Data/Application/****/Library/assortiment.json
2019-11-13 14:01:18.5303|INFO|persistenceLogger|Dropbox downloader called.
2019-11-13 14:01:19.2375|INFO|persistenceLogger|Writing /****_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/****/data/Containers/Data/Application/****/Library/assortiment.json
但对于两个计时器导致如此不同行为的原因，我仍然愿意接受开明的解释。
我有一个移动跨平台 Xamarin.Forms 项目，我在其中尝试在启动时从 Dropbox 存储库下载文件。这是一个小于 50kB 的 json 文件。操作 Dropbox API 调用的代码在我的 Android 和我的 iOS 项目之间共享，并且我的 Android 实现按预期工作。这是一个 Task 方法，为了方便起见，我在这里将其称为 downloader。
更新： 使用 iOS 版本，我只能在调用 downloader 的启动器（这也是一个任务）时才能成功下载文件) 直接来自我唯一的 AppDelegate 的 BackgroundSynchronizer.Launch() 方法，但在使用计时器委托此调用通过调用 EventHandler 调用我的 downloader 时则不会] 重复出现。
我不明白为什么。
downloader：
public class DropboxStorage : IDistantStoreService
{
private string oAuthToken;
private DropboxClientConfig clientConfig;
private Logger logger = new Logger
(DependencyService.Get<ILoggingBackend>());
public DropboxStorage()
{
var httpClient = new HttpClient(new NativeMessageHandler());
clientConfig = new DropboxClientConfig
{
HttpClient = httpClient
};
}
public async Task SetConnection()
{
await GetAccessToken();
}
public async Task<Stream> DownloadFile(string distantUri)
{
logger.Info("Dropbox downloader called.");
try
{
await SetConnection();
using var client = new DropboxClient(oAuthToken, clientConfig);
var downloadArg = new DownloadArg(distantUri);
var metadata = await client.Files.DownloadAsync(downloadArg);
var stream = metadata?.GetContentAsStreamAsync();
return await stream;
}
catch (Exception ex)
{
logger.Error(ex);
}
return null;
}
更新： AppDelegate：
using Foundation;
using UIKit;
namespace Izibio.iOS
{
// The UIApplicationDelegate for the application. This class is responsible for launching the
// User Interface of the application, as well as listening (and optionally responding) to
// application events from iOS.
[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
private BackgroundSynchronizer synchronizer = new BackgroundSynchronizer();
//
// This method is invoked when the application has loaded and is ready to run. In this
// method you should instantiate the window, load the UI into it and then make the window
// visible.
//
// You have 17 seconds to return from this method, or iOS will terminate your application.
//
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init();
LoadApplication(new App());
return base.FinishedLaunching(app, options);
}
public override void OnActivated(UIApplication uiApplication)
{
synchronizer.Launch();
base.OnActivated(uiApplication);
}
}
}
编辑： 中介 class（嵌入了 DownloadProducts 功能）：
public static class DropboxNetworkRequests
{
public static async Task DownloadProducts(IDistantStoreService distantStorage,
IStoreService localStorage)
{
try
{
var productsFileName = Path.GetFileName(Globals.ProductsFile);
var storeDirectory = $"/{Globals.StoreId}_products";
var productsFileUri = Path.Combine(storeDirectory, productsFileName);
var stream = await distantStorage.DownloadFile(productsFileUri);
if (stream != null)
{
await localStorage.Save(stream, productsFileUri);
}
else
{
var logger = GetLogger();
logger.Info($"No file with the uri ’{productsFileUri}’ could " +
$"have been downloaded.");
}
}
catch (Exception ex)
{
var logger = GetLogger();
logger.Error(ex);
}
}
private static Logger GetLogger()
{
var loggingBackend = DependencyService.Get<ILoggingBackend>();
return new Logger(loggingBackend);
}
}
更新： 和失败的启动器 class（Launch 方法中注释的 TriggerNetworkOperations(this, EventArgs.Empty);
成功下载文件）：
public class BackgroundSynchronizer
{
private bool isDownloadRunning;
private IDistantStoreService distantStorage;
private IStoreService localStorage;
private Timer timer;
public event EventHandler SynchronizationRequested;
public BackgroundSynchronizer()
{
Forms.Init();
isDownloadRunning = false;
distantStorage = DependencyService.Get<IDistantStoreService>();
localStorage = DependencyService.Get<IStoreService>();
Connectivity.ConnectivityChanged += TriggerNetworkOperations;
SynchronizationRequested += TriggerNetworkOperations;
}
public void Launch()
{
try
{
var millisecondsInterval = Globals.AutoDownloadMillisecondsInterval;
var callback = new TimerCallback(SynchronizationCallback);
timer = new Timer(callback, this, 0, 0);
timer.Change(0, millisecondsInterval);
//TriggerNetworkOperations(this, EventArgs.Empty);
}
catch (Exception ex)
{
throw ex;
}
}
protected virtual void OnSynchronizationRequested(object sender, EventArgs e)
{
SynchronizationRequested?.Invoke(sender, e);
}
private async void TriggerNetworkOperations(object sender, ConnectivityChangedEventArgs e)
{
if ((e.NetworkAccess == NetworkAccess.Internet) && !isDownloadRunning)
{
await DownloadProducts(sender);
}
}
private async void TriggerNetworkOperations(object sender, EventArgs e)
{
if (!isDownloadRunning)
{
await DownloadProducts(sender);
}
}
private void SynchronizationCallback(object state)
{
SynchronizationRequested(state, EventArgs.Empty);
}
private async Task DownloadProducts(object sender)
{
var instance = (BackgroundSynchronizer)sender;
//Anti-reentrance assignments commented for debugging purposes
//isDownloadRunning = true;
await DropboxNetworkRequests.DownloadProducts(instance.distantStorage, instance.localStorage);
//isDownloadRunning = false;
}
}
我设置了一个日志文件来记录我尝试下载时的应用程序行为。
编辑： 以下是我从 Launch 方法直接调用 TriggerNetworkOperations 时收到的消息：
2019-11-12 19:31:57.1758|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-12 19:31:57.4875|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:31:58.4810|INFO|persistenceLogger|Writing /MAZEDI_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/5BABB56B-9B42-4653-9D3E-3C60CFFD50A8/data/Containers/Data/Application/D6C517E9-3446-4916-AD8D-565F4C206AF2/Library/assortiment.json
编辑： 是我在通过计时器及其回调启动时得到的（用于调试的间隔为 10 秒）：
2019-11-12 19:34:05.5166|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-12 19:34:05.8149|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:15.8083|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:25.8087|INFO|persistenceLogger|Dropbox downloader called.
2019-11-12 19:34:35.8089|INFO|persistenceLogger|Dropbox downloader called.
编辑： 在第二种情况下，启动的任务事件最终被 OS:
取消2019-11-13 09:36:29.7359|ERROR|persistenceLogger|System.Threading.Tasks.TaskCanceledException: A task was canceled.
at ModernHttpClient.NativeMessageHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x002a5] in /Users/paul/code/paulcbetts/modernhttpclient/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs:139
at System.Net.Http.HttpClient.SendAsyncWorker (System.Net.Http.HttpRequestMessage request, System.Net.Http.HttpCompletionOption completionOption, System.Threading.CancellationToken cancellationToken) [0x0009e] in /Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/external/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:281
at Dropbox.Api.DropboxRequestHandler.RequestJsonString (System.String host, System.String routeName, System.String auth, Dropbox.Api.DropboxRequestHandler+RouteStyle routeStyle, System.String requestArg, System.IO.Stream body) [0x0030f] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Dropbox.Api.DropboxRequestHandler.RequestJsonStringWithRetry (System.String host, System.String routeName, System.String auth, Dropbox.Api.DropboxRequestHandler+RouteStyle routeStyle, System.String requestArg, System.IO.Stream body) [0x000f6] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Dropbox.Api.DropboxRequestHandler.Dropbox.Api.Stone.ITransport.SendDownloadRequestAsync[TRequest,TResponse,TError] (TRequest request, System.String host, System.String route, System.String auth, Dropbox.Api.Stone.IEncoder`1[T] requestEncoder, Dropbox.Api.Stone.IDecoder`1[T] resposneDecoder, Dropbox.Api.Stone.IDecoder`1[T] errorDecoder) [0x000a5] in <8d8475f2111a4ae5850a1c1349c08d28>:0
at Izibio.Persistence.DropboxStorage.DownloadFile (System.String distantUri) [0x00105] in /Users/dev3/Virtual Machines.localized/shared/TRACAVRAC/izibio-mobile/Izibio/Izibio.Persistence/Services/DropboxStorage.cs:44
2019-11-13 09:36:29.7399|INFO|persistenceLogger|No file with the uri ’/******_products/assortiment.json’ could have been downloaded.
我将简单地添加最后一个观察结果：当从 BackgroundSynchronizer 调试 DownloadFile 任务时，我可以到达对 client.Files.DowloadAsync 的调用：var metadata = await client.Files.DownloadAsync(downloadArg);，但是我不会从此等待语句中检索任何 return。
好的，我终于找到了解决这个问题的方法，方法是用 iOS 实现 (NSTimer) 替换 .NET 计时器。
我的 BackgroundSynchronizer 新代码 class：
public class BackgroundSynchronizer
{
private bool isDownloadRunning;
private IDistantStoreService distantStorage;
private IStoreService localStorage;
private NSTimer timer;
public event EventHandler SynchronizationRequested;
public BackgroundSynchronizer()
{
Forms.Init();
isDownloadRunning = false;
distantStorage = DependencyService.Get<IDistantStoreService>();
localStorage = DependencyService.Get<IStoreService>();
Connectivity.ConnectivityChanged += TriggerNetworkOperations;
SynchronizationRequested += TriggerNetworkOperations;
}
public void Launch()
{
try
{
var seconds = Globals.AutoDownloadMillisecondsInterval / 1000;
var interval = new TimeSpan(0, 0, seconds);
var callback = new Action<NSTimer>(SynchronizationCallback);
StartTimer(interval, callback);
}
catch (Exception ex)
{
throw ex;
}
}
protected virtual void OnSynchronizationRequested(object sender, EventArgs e)
{
SynchronizationRequested?.Invoke(sender, e);
}
private async void TriggerNetworkOperations(object sender, ConnectivityChangedEventArgs e)
{
if ((e.NetworkAccess == NetworkAccess.Internet) && !isDownloadRunning)
{
await DownloadProducts();
}
}
private async void TriggerNetworkOperations(object sender, EventArgs e)
{
if (!isDownloadRunning)
{
await DownloadProducts();
}
}
private void SynchronizationCallback(object state)
{
SynchronizationRequested(state, EventArgs.Empty);
}
private async Task DownloadProducts()
{
isDownloadRunning = true;
await DropboxNetworkRequests.DownloadProducts(distantStorage, localStorage);
isDownloadRunning = false;
}
private void StartTimer(TimeSpan interval, Action<NSTimer> callback)
{
timer = NSTimer.CreateRepeatingTimer(interval, callback);
NSRunLoop.Main.AddTimer(timer, NSRunLoopMode.Common);
}
}
产生以下日志行：
2019-11-13 14:00:58.2086|INFO|xamarinLogger|iZiBio Mobile Launched
2019-11-13 14:01:08.5378|INFO|persistenceLogger|Dropbox downloader called.
2019-11-13 14:01:09.5656|INFO|persistenceLogger|Writing /****_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/****/data/Containers/Data/Application/****/Library/assortiment.json
2019-11-13 14:01:18.5303|INFO|persistenceLogger|Dropbox downloader called.
2019-11-13 14:01:19.2375|INFO|persistenceLogger|Writing /****_products/assortiment.json at /Users/dev3/Library/Developer/CoreSimulator/Devices/****/data/Containers/Data/Application/****/Library/assortiment.json
但对于两个计时器导致如此不同行为的原因，我仍然愿意接受开明的解释。