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| title | author | description | monikerRange | ms.author | ms.custom | ms.date | no-loc | uid | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Host ASP.NET Core SignalR in background services | bradygaster | Learn how to send messages to SignalR clients from .NET Core BackgroundService classes. | >= aspnetcore-2.2 | bradyg | mvc | 11/12/2019 |
|
signalr/background-services |
Host ASP.NET Core SignalR in background services
By Brady Gaster
This article provides guidance for:
- Hosting SignalR Hubs using a background worker process hosted with ASP.NET Core.
- Sending messages to connected clients from within a .NET Core BackgroundService.
::: moniker range=">= aspnetcore-3.0"
View or download sample code (how to download)
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
View or download sample code (how to download)
::: moniker-end
Enable SignalR in startup
::: moniker range=">= aspnetcore-3.0"
Hosting ASP.NET Core SignalR Hubs in the context of a background worker process is identical to hosting a Hub in an ASP.NET Core web app. In the Startup.ConfigureServices method, calling services.AddSignalR adds the required services to the ASP.NET Core Dependency Injection (DI) layer to support SignalR. In Startup.Configure, the MapHub method is called in the UseEndpoints callback to connect the Hub endpoints in the ASP.NET Core request pipeline.
[!code-csharpStartup]
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
Hosting ASP.NET Core SignalR Hubs in the context of a background worker process is identical to hosting a Hub in an ASP.NET Core web app. In the Startup.ConfigureServices method, calling services.AddSignalR adds the required services to the ASP.NET Core Dependency Injection (DI) layer to support SignalR. In Startup.Configure, the UseSignalR method is called to connect the Hub endpoint(s) in the ASP.NET Core request pipeline.
[!code-csharpStartup]
::: moniker-end
In the preceding example, the ClockHub class implements the Hub<T> class to create a strongly typed Hub. The ClockHub has been configured in the Startup class to respond to requests at the endpoint /hubs/clock.
For more information on strongly typed Hubs, see Use hubs in SignalR for ASP.NET Core.
[!NOTE] This functionality isn't limited to the Hub<T> class. Any class that inherits from Hub, such as DynamicHub, works.
::: moniker range=">= aspnetcore-3.0"
[!code-csharpStartup]
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
[!code-csharpStartup]
::: moniker-end
The interface used by the strongly typed ClockHub is the IClock interface.
::: moniker range=">= aspnetcore-3.0"
[!code-csharpStartup]
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
[!code-csharpStartup]
::: moniker-end
Call a SignalR Hub from a background service
During startup, the Worker class, a BackgroundService, is enabled using AddHostedService.
services.AddHostedService<Worker>();
Since SignalR is also enabled up during the Startup phase, in which each Hub is attached to an individual endpoint in ASP.NET Core's HTTP request pipeline, each Hub is represented by an IHubContext<T> on the server. Using ASP.NET Core's DI features, other classes instantiated by the hosting layer, like BackgroundService classes, MVC Controller classes, or Razor page models, can get references to server-side Hubs by accepting instances of IHubContext<ClockHub, IClock> during construction.
::: moniker range=">= aspnetcore-3.0"
[!code-csharpStartup]
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
[!code-csharpStartup]
::: moniker-end
As the ExecuteAsync method is called iteratively in the background service, the server's current date and time are sent to the connected clients using the ClockHub.
React to SignalR events with background services
Like a Single Page App using the JavaScript client for SignalR, or a .NET desktop app using the xref:signalr/dotnet-client, a BackgroundService or IHostedService implementation can also be used to connect to SignalR Hubs and respond to events.
The ClockHubClient class implements both the IClock interface and the IHostedService interface. This way it can be enabled during Startup to run continuously and respond to Hub events from the server.
public partial class ClockHubClient : IClock, IHostedService
{
}
During initialization, the ClockHubClient creates an instance of a HubConnection and enables the IClock.ShowTime method as the handler for the Hub's ShowTime event.
::: moniker range=">= aspnetcore-3.0"
[!code-csharpThe ClockHubClient constructor]
In the IHostedService.StartAsync implementation, the HubConnection is started asynchronously.
[!code-csharpStartAsync method]
During the IHostedService.StopAsync method, the HubConnection is disposed of asynchronously.
[!code-csharpStopAsync method]
::: moniker-end ::: moniker range="<= aspnetcore-2.2"
[!code-csharpThe ClockHubClient constructor]
In the IHostedService.StartAsync implementation, the HubConnection is started asynchronously.
[!code-csharpStartAsync method]
During the IHostedService.StopAsync method, the HubConnection is disposed of asynchronously.
[!code-csharpStopAsync method]
::: moniker-end