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Scoped service behavior in Blazor Server apps (#20806)

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Luke Latham 2020-12-02 11:02:29 -06:00 committed by GitHub
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aspnetcore/blazor/fundamentals/dependency-injection.md
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@ -137,7 +137,7 @@ Services can be configured with the lifetimes shown in the following table.
| Lifetime | Description |
| -------- | ----------- |
| <xref:Microsoft.Extensions.DependencyInjection.ServiceDescriptor.Scoped%2A> | Blazor WebAssembly apps don't currently have a concept of DI scopes. `Scoped`-registered services behave like `Singleton` services. However, the Blazor Server hosting model supports the `Scoped` lifetime. In Blazor Server apps, a scoped service registration is scoped to the *connection*. For this reason, using scoped services is preferred for services that should be scoped to the current user, even if the current intent is to run client-side in the browser in a Blazor WebAssembly app. |
| <xref:Microsoft.Extensions.DependencyInjection.ServiceDescriptor.Scoped%2A> | <p>Blazor WebAssembly apps don't currently have a concept of DI scopes. `Scoped`-registered services behave like `Singleton` services.</p><p>The Blazor Server hosting model supports the `Scoped` lifetime across HTTP requests but not across SingalR connection/circuit messages among components that are loaded on the client. The Razor Pages or MVC portion of the app treats scoped services normally and recreates the services on *each HTTP request* when navigating among pages or views or from a page or view to a component. Scoped services aren't reconstructed when navigating among components on the client, where the communication to the server takes place over the SignalR connection of the user's circuit, not via HTTP requests. In the following component scenarios on the client, scoped services are reconstructed because a new circuit is created for the user:</p><ul><li>The user closes the browser's window. The user opens a new window and navigates back to the app.</li><li>The user closes the last tab of the app in a browser window. The user opens a new tab and navigates back to the app.</li><li>The user selects the browser's reload/refresh button.</li></ul><p>For more information on preserving user state across scoped services in Blazor Server apps, see <xref:blazor/hosting-models?pivots=server>.</p> |
| <xref:Microsoft.Extensions.DependencyInjection.ServiceDescriptor.Singleton%2A> | DI creates a *single instance* of the service. All components requiring a `Singleton` service receive an instance of the same service. |
| <xref:Microsoft.Extensions.DependencyInjection.ServiceDescriptor.Transient%2A> | Whenever a component obtains an instance of a `Transient` service from the service container, it receives a *new instance* of the service. |