Add support for hosted services in .NET MAUI apps

[Eilon]

Look into using hosted services. This would replace the icky IMauiInitializeService that was added in #2137, and also to enable users to use hosted services. MAUI will automatically call StartAsync/StopAsync at the appropriate time. Sadly, this pattern is async-only, whereas in MAUI the call sites are always (or at least almost always) sync. But given that this is app startup/shutdown, doing async-over-sync might be OK (we would block).

This is a follow-up to PR #2137.

Other notes:

• Need to consider this when implementing: Run user defined hosted services before the server starts. aspnetcore#36122

[halter73]

But given that this is app startup/shutdown, doing async-over-sync might be OK (we would block).

I think this is reasonable. That's effectively what happens when a Program.Main() uses the generic host. Even with an async Program.Main(), the compiler synthesizes the real entry point which blocks.

[pjmagee]

Just to clarify my understanding, this would mean once supported i could drop the following icky code I'm using? I pass the IHostEnvironment environment to some wiring code, The maui App assembly is just "HeroesProfile", but i use shared IoC registration. To give some context on how I'm using DI.

 /*
             * Hosted services only works with the Hosting Extensions from .NET
             * Maui does not use the same Hosting service and so we much register them differently depending on how we execute background services.
             * If this is for Maui, we must hook into Application startup and run the services.
             * If this is for Console, .AddHostedService will handle starting the services for us.
             */
            if (environment.ApplicationName.Equals("HeroesProfile.Console"))
            {
                services
                    .AddHostedService<GameSimulator>()
                    .AddHostedService<FileWatchers>()
                    .AddHostedService<OnLaunchReplayProcessor>();
            }
            else
            {
                services
                    .AddSingleton<GameSimulator>()
                    .AddSingleton<FileWatchers>()
                    .AddSingleton<OnLaunchReplayProcessor>();
            }

[Eilon]

@pjmagee yeah I think so. If we implement this, there would be proper support for hosted services so all the regular APIs that exist for that would work as expected (starting/stopping those services).

[RayKoopa]

Dumb question hopefully not too off-topic; what does an IHostedService mean on Android? Will that behave like an Android foreground service or will it only live as long as the MAUI app is running? I want to run an always-on .NET 5 BackgroundService on my Android smartphone and am a little lost figuring out how to utilize MAUI or net6.0-android for that yet.

[Eilon]

@RayKoopa - This would be for in-app in-proc services. So they would start when the app starts, and dies when the app dies. I'm not sure in Android terminology what that equates to, but it's not a background thing.

[RayKoopa]

@Eilon Ah alright, I expected it to be "app-wide". I'll try to figure out how to host my Android foreground service then (which is like a "system-wide" background thread with a notification, that has no connection to an app or UI once started). Thanks for the fast reply!

[hflexgrig]

Any news from this issue?

[hflexgrig]

@Eilon Added pull request for this issue #3718

[Eilon]

@hflexgrig oh wow I'll take a look!

[hflexgrig]

@Eilon deleted old one and create new #3724

[obenyaala]

any status on this feature? Thanks

[ctigrisht]

will there ever be hosted services?

[kevinchalet]

FWIW, having native IHostedService support would allow OpenIddict users to use the new OpenIddict.Client.SystemIntegration package on MAUI/WinUI. I posted more information here: openiddict/openiddict-core#1480 (comment).

[JohnHunterACS]

This kind of addition would definitely make it easier to work with an abstracted service model instead of platform specific service implementations.

[DoubleDBE]

Any news about this? Currently stuck because of this...

[Eilon]

This work is not currently planned. Could you manually start the services in MauiProgram or another part of the app? Certainly not ideal, but it could be a reasonable workaround.

[janseris]

This work is not currently planned. Could you manually start the services in MauiProgram or another part of the app? Certainly not ideal, but it could be a reasonable workaround.

Does this really work in Android when screen is switched off?