Implement iOS background http call support

README.md

@@ -6,6 +6,33 @@
 
 `Nalu.Maui` provides a set of classes to help you with everyday challenges encountered while working with .NET MAUI.
 
+### Core [![Nalu.Maui.Core NuGet Package](https://img.shields.io/nuget/v/Nalu.Maui.Core.svg)](https://www.nuget.org/packages/Nalu.Maui.Core/) [![Nalu.Maui NuGet Package Downloads](https://img.shields.io/nuget/dt/Nalu.Maui.Core)](https://www.nuget.org/packages/Nalu.Maui.Core/)
+
+The core library is intended to provide a set of common use utilities.
+
+Have you ever noticed that when the user backgrounds the app on iOS, the app is suspended, and the network requests will fail due to `The network connection was lost`?
+
+This is really annoying: it forces us to implement complex retry logic, especially considering that the request may have already hit the server.
+
+To solve this issue, we provide a `NSUrlBackgroundSessionHttpMessageHandler` to be used in your `HttpClient` to allow http request to continue even when the app is in the background.
+
+```csharp
+#if IOS
+    var client = new HttpClient(new NSUrlBackgroundSessionHttpMessageHandler());
+#else
+    var client = new HttpClient();
+#endif
+```
+
+To make this work, you need to change your `AppDelegate` as follows:
+```csharp
+[Export("application:handleEventsForBackgroundURLSession:completionHandler:")]
+public virtual void HandleEventsForBackgroundUrl(UIApplication application, string sessionIdentifier, Action completionHandler)
+    => NSUrlBackgroundSessionHttpMessageHandler.HandleEventsForBackgroundUrl(application, sessionIdentifier, completionHandler);
+```
+
+**Check out the [Core Wiki](core.html) for more information**.
+
 ### Navigation [![Nalu.Maui.Navigation NuGet Package](https://img.shields.io/nuget/v/Nalu.Maui.Navigation.svg)](https://www.nuget.org/packages/Nalu.Maui.Navigation/) [![Nalu.Maui NuGet Package Downloads](https://img.shields.io/nuget/dt/Nalu.Maui.Navigation)](https://www.nuget.org/packages/Nalu.Maui.Navigation/)
 
 The MVVM navigation service offers a straightforward and robust method for navigating between pages and passing parameters.

Samples/Nalu.Maui.Sample/MauiProgram.cs

@@ -64,10 +64,24 @@ public static MauiApp CreateMauiApp()
 
 #if DEBUG
         builder.Logging.AddDebug();
+        builder.Logging.SetMinimumLevel(LogLevel.Debug);
 #endif
 
         builder.Services.AddTransientPopup<CanLeavePopup, CanLeavePopupModel>();
 
+        builder.Services.AddKeyedSingleton<HttpClient>("dummyjson", (_, _) =>
+        {
+#if IOS
+            var client = new HttpClient(new NSUrlBackgroundSessionHttpMessageHandler())
+#else
+            var client = new HttpClient()
+#endif
+            {
+                BaseAddress = new Uri("https://dummyjson.com/")
+            };
+            return client;
+        });
+
         return builder.Build();
     }
 }

Samples/Nalu.Maui.Sample/PageModels/OnePageModel.cs

@@ -1,5 +1,6 @@
 namespace Nalu.Maui.Sample.PageModels;
 
+using System.Net.Http.Json;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 
@@ -8,14 +9,81 @@ public class AnimalModel
     public string Name { get; set; } = null!;
 }
 
-public partial class OnePageModel(INavigationService navigationService) : ObservableObject
+public partial class OnePageModel(
+    INavigationService navigationService,
+    [FromKeyedServices("dummyjson")] HttpClient httpClient) : ObservableObject
 {
     private static int _instanceCount;
 
-    public AnimalModel Animal { get; } = new AnimalModel { Name = "Dog" };
+    [ObservableProperty]
+    private string? _result1;
+
+    [ObservableProperty]
+    private string? _result2;
+
+    [ObservableProperty]
+    private string? _result3;
+
+    [ObservableProperty]
+    private string? _result4;
+
+    public AnimalModel Animal { get; } = new() { Name = "Dog" };
 
     public int InstanceCount { get; } = Interlocked.Increment(ref _instanceCount);
 
     [RelayCommand(AllowConcurrentExecutions = false)]
     private Task PushThreeAsync() => navigationService.GoToAsync(Navigation.Relative().Push<ThreePageModel>());
+
+    [RelayCommand]
+    private async Task SendRequestAsync()
+    {
+        Result1 = null;
+        Result2 = null;
+        Result3 = null;
+        Result4 = null;
+
+        var parallelRequestTask1 = SendRequestAsync(CreateTestLongRequest(5000));
+        Result1 = "waiting...";
+        var parallelRequestTask2 = SendRequestAsync(CreateTestLongRequest(4000));
+        Result2 = "waiting...";
+
+        Result1 = await parallelRequestTask1;
+        Result2 = await parallelRequestTask2;
+
+        var followUpRequest = SendRequestAsync(CreateTestLongRequest(5000));
+        Result3 = "waiting...";
+        Result3 = await followUpRequest;
+
+        var followUpRequest2 = SendRequestAsync(CreateTestLongRequest(999999));
+        Result4 = "waiting...";
+        Result4 = await followUpRequest2;
+    }
+
+    private async Task<string> SendRequestAsync(HttpRequestMessage requestMessage)
+    {
+        string result;
+        try
+        {
+            var responseMessage = await httpClient.SendAsync(requestMessage);
+            result = await responseMessage.Content.ReadAsStringAsync();
+        }
+        catch (Exception e)
+        {
+            result = e.Message;
+        }
+
+        return result;
+    }
+
+    /// <summary>
+    /// Creates a request to an endpoint that will delay the response.
+    /// See https://dummyjson.com/docs#intro-test for more information.
+    /// </summary>
+    private HttpRequestMessage CreateTestLongRequest(int delayMs = 5000) =>
+        new()
+        {
+            RequestUri = new Uri($"test?delay={delayMs}", UriKind.Relative),
+            Method = HttpMethod.Post,
+            Content = JsonContent.Create(Animal),
+        };
 }

Samples/Nalu.Maui.Sample/Pages/OnePage.xaml

@@ -17,6 +17,46 @@
                    Aspect="AspectFit"
                    Margin="0,16,0,24"/>
 
+            <Button Command="{Binding SendRequestCommand}"
+                    Text="Send requests"
+                    HorizontalOptions="Center" />
+
+            <Label>
+                <Label.FormattedText>
+                    <FormattedString>
+                        <Span Text="Parallel Request 1: " />
+                        <Span Text="{Binding Result1}" />
+                    </FormattedString>
+                </Label.FormattedText>
+            </Label>
+
+            <Label>
+                <Label.FormattedText>
+                    <FormattedString>
+                        <Span Text="Parallel Request 2: " />
+                        <Span Text="{Binding Result2}" />
+                    </FormattedString>
+                </Label.FormattedText>
+            </Label>
+
+            <Label>
+                <Label.FormattedText>
+                    <FormattedString>
+                        <Span Text="Follow-up Request 3: " />
+                        <Span Text="{Binding Result3}" />
+                    </FormattedString>
+                </Label.FormattedText>
+            </Label>
+
+            <Label>
+                <Label.FormattedText>
+                    <FormattedString>
+                        <Span Text="Erroring Request 4: " />
+                        <Span Text="{Binding Result4}" />
+                    </FormattedString>
+                </Label.FormattedText>
+            </Label>
+
             <Label>
                 <Label.FormattedText>
                     <FormattedString>

Samples/Nalu.Maui.Sample/Platforms/iOS/AppDelegate.cs

@@ -1,9 +1,14 @@
 namespace Nalu.Maui.Sample;
 
 using Foundation;
+using UIKit;
 
 [Register("AppDelegate")]
 public class AppDelegate : MauiUIApplicationDelegate
 {
     protected override MauiApp CreateMauiApp() => MauiProgram.CreateMauiApp();
+
+    [Export("application:handleEventsForBackgroundURLSession:completionHandler:")]
+    public virtual void HandleEventsForBackgroundUrl(UIApplication application, string sessionIdentifier, Action completionHandler)
+        => NSUrlBackgroundSessionHttpMessageHandler.HandleEventsForBackgroundUrl(application, sessionIdentifier, completionHandler);
 }

Source/Nalu.Maui.Core/Nalu.Maui.Core.csproj

@@ -40,7 +40,6 @@
 
   <ItemGroup>
     <Folder Include="Platforms\Android\" />
-    <Folder Include="Platforms\iOS\" />
     <Folder Include="Platforms\MacCatalyst\" />
   </ItemGroup>
 </Project>