Add chapter about dependency injection in Blazor #14

rstropek · 2018-04-03T06:00:47Z

Fixes #6

This pull request adds a chapter about DI in Blazor as discussed with @guardrex. Compared to the version he reviewed, I added a code sample at the end of the document showing how to implement IDisposable in a Blazor component.

dnfclas · 2018-04-03T06:00:58Z

All CLA requirements met.

guardrex · 2018-04-03T15:23:59Z

Thank you @rstropek! 🎸

SteveSandersonMS

This is great - nice clear explanations!

SteveSandersonMS · 2018-04-04T22:03:37Z

docs/dependency-injection.md

+
+Blazor has [dependency injection (DI)](https://docs.microsoft.com/aspnet/core/fundamentals/dependency-injection) built-in. Blazor apps can use built-in services by having them injected into components. Blazor apps can also define custom services and make them available via DI.
+
+## What is dependency injection?


Firstly, I really like the overall tone of voice here and think this is just the right amount of background detail. Great job!

Secondly, I slightly object to the idea that "component should not create an instance of DataAccess" as if that were always true. That's entirely the choice of the application developer. Sometimes there's value in working with an abstraction; sometimes it would just be unnecessary friction. It depends on the scenario. The DI system in Blazor is equally happy to supply instances of concrete service classes as it is to deal with interfaces.

I'd say something like:

DI is a technique for accessing services configured in a central location. This can be useful if:

You want to share a single instance of a service class across many components (known as a "singleton" service)

Or, if you want to decouple components from particular concrete service classes and only reference abstract interfaces. For example, you might have an interface IDataAccess implemented by a concrete class DataAccess. If your components use DI to receive an IDataAccess implementation, they aren't coupled to any concrete type. That means the implementation could easily be swapped, perhaps to a mock implementation in unit tests.

Blazor's DI system is responsible for supplying instances of services to components. It also resolves dependencies recursively, so that services themselves can depend on further services, and so on. DI is configured during startup of the app. An example is shown later in this topic.

SteveSandersonMS · 2018-04-04T22:05:49Z

docs/dependency-injection.md

+
+Blazor's implementation of `System.IServiceProvider` obtains its services from an underlying [Microsoft.Extensions.DependencyInjection.IServiceCollection](https://docs.microsoft.com/dotnet/api/microsoft.extensions.dependencyinjection.iservicecollection).
+
+## Add services to DI


Cool - good explanation about configuration!

SteveSandersonMS · 2018-04-04T22:07:55Z

docs/dependency-injection.md

+| Method       | Description |
+| ------------ | ----------- |
+| `IUriHelper` | Helpers for working with URIs and navigation state (singleton). |
+| `HttpClient` | Provides methods for sending HTTP requests and receiving HTTP responses from a resource identified by a URI (singleton). Note that this instance of [System.Net.Http.HttpClient](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient) is using the browser for handling the HTTP traffic in the background. Its [BaseAddress](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient.baseaddress) is automatically set to the base URI prefix of the Blazor app. |


In a couple of places it says "is using" or "is referencing". Maybe it's a language difference, but a more common phrasing would be simply "uses" or "references". Not a big deal though!

SteveSandersonMS · 2018-04-04T22:10:09Z

docs/dependency-injection.md

+| `IUriHelper` | Helpers for working with URIs and navigation state (singleton). |
+| `HttpClient` | Provides methods for sending HTTP requests and receiving HTTP responses from a resource identified by a URI (singleton). Note that this instance of [System.Net.Http.HttpClient](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient) is using the browser for handling the HTTP traffic in the background. Its [BaseAddress](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient.baseaddress) is automatically set to the base URI prefix of the Blazor app. |
+
+## Request a service in a component


I like this section - well explained!

SteveSandersonMS · 2018-04-04T22:10:43Z

docs/dependency-injection.md

+
+## Dependency injection in services
+
+Complex services might require additional services. In the prior example, `DataAccess` might require Blazor's default service `HttpClient`. `@inject` or the `InjectAttribute` can't be used in services. *Constructor injection* must be used instead. Require services are added by adding parameters to the service's constructor. When dependency injection creates the service, it recognizes the services it requires in the constructor and provides them accordingly.


Typo: "Require services" should be "Required services"

SteveSandersonMS · 2018-04-04T22:12:05Z

docs/dependency-injection.md

+
+## System services
+
+Blazor provides default services that are automatically added to the service collection of a Blazor app. The following table shows a list of the default services currently provided by Blazor.


I wonder if it's worth clarifying that these are the default services in a BrowserServiceProvider (which is what the project template uses by default in Program.cs). If someone creates their own different service provider, it wouldn't contain these services.

guardrex · 2018-04-05T15:45:58Z

I only see a handful of very minor grammatical changes to make. To save time, I'm just going to shoot them in there and then sign off. Stand by ....

guardrex

This topic is 🔥 HOT HOT HOT 🔥 ... great job!

Thanks again @rstropek for handling this issue. 🚀

@danroth27 @SteveSandersonMS Do you have anything else here before merging? @rynowak ... do you have comments?

danroth27

Looks great! Just a few small comments.

danroth27 · 2018-04-05T17:14:18Z

docs/dependency-injection.md

+
+Blazor's DI system is responsible for supplying instances of services to components. DI also resolves dependencies recursively so that services themselves can depend on further services. DI is configured during startup of the app. An example is shown later in this topic.
+
+## Use of existing .NET mechanisms


I don't think this section adds much and it delays getting into content that helps you get started using DI. I think I would just remove it.

danroth27 · 2018-04-05T17:15:17Z

docs/dependency-injection.md

+{
+    var serviceProvider = new BrowserServiceProvider(configure =>
+    {
+        configure.Add(ServiceDescriptor.Singleton<IDataAccess, DataAccess>());


This should just be configure.AddSingleton<IDataAccess, DataAccess>(); You just need to add a using for Microsoft.Extensions.DependencyInjection.

danroth27 · 2018-04-05T17:18:34Z

docs/dependency-injection.md

+}
+```
+
+`ServiceDescriptor` offers several overloads of three methods that are used to add services to Blazor's DI:


I think of ServiceDescriptor as being a lower level concept. Most of the time you just use the extension methods. I suggest replacing this sentence with: "Services can be configured with the following lifetimes:"

danroth27 · 2018-04-05T17:19:47Z

docs/dependency-injection.md

+| `IUriHelper` | Helpers for working with URIs and navigation state (singleton). |
+| `HttpClient` | Provides methods for sending HTTP requests and receiving HTTP responses from a resource identified by a URI (singleton). Note that this instance of [System.Net.Http.HttpClient](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient) uses the browser for handling the HTTP traffic in the background. Its [BaseAddress](https://docs.microsoft.com/dotnet/api/system.net.http.httpclient.baseaddress) is automatically set to the base URI prefix of the app. |
+
+Note that it is possible to use a custom services provider instead of the default `BrowserServiceProvider` that's added by the default template. A custom service provider doesn't automatically provide the default services listed in the table. Those services must be added to the new service provider explicitly.


@SteveSandersonMS Is this a bug? Shouldn't we populate the custom service provider with the default services?

That’s not something we have the option to do. If the developer provides their own IServiceProvider we can’t control what it returns; it’s up to them to delegate calls to a BrowserServiceProvider if they want to.

That seems surprisingly different to how things work in ASP.NET Core. In ASP.NET Core you can switch to using a different IoC container (Autofac or whatever) but you still get the host provided services. But no need to hold up this PR on this discussion as the doc is currently correct.

danroth27 · 2018-04-05T17:20:30Z

docs/dependency-injection.md

+}
+```
+
+In components derived from the base class, the `@inject` directive isn't required. The `InjectAttribute` of the base class is satisfactory:


satisfactory -> sufficient

danroth27 · 2018-04-05T17:21:59Z

docs/dependency-injection.md

+        ...
+    }
+}
+```


I think we need a link to https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection somewhere. Maybe just have an additional resources section at the end?

danroth27 · 2018-04-05T17:23:53Z

docs/dependency-injection.md

+
+## Service lifetime
+
+Note that Blazor doesn't automatically dispose injected services that implement `IDisposable`. Components can implement `IDisposable`. Services are disposed when the user navigates away from the component.


Services are disposed when the user navigates away from the component.

I think this should say: "Components are disposed when the user navigates away from the component, at which point the component can dispose any transient services"

guardrex · 2018-04-05T17:35:06Z

Fixed everything outside of the custom service provider with the default services question.

danroth27 · 2018-04-05T17:42:32Z

docs/dependency-injection.md

+```csharp
+static void Main(string[] args)
+{
+    var serviceProvider = new BrowserServiceProvider(configure =>


One more thing: I'm proposing that rename configure to services so that it's consistent with ASP.NET Core.

dotnet/blazor#494

guardrex · 2018-04-05T17:43:34Z

@danroth27 One little thing tho that I find strange about this one ...

Components are disposed when the user navigates away from the component, then the component can dispose any transient services.

If the component is disposed when the user navigates away ... then how can it dispose transient services? ... It reads like it's doing something after it has been destroyed.

Can we restructure it? ... e.g. ...

Components and their transient services are disposed when the user navigates away from the component.

[EDIT] I used that ☝️ version. Let me know if we need to revert or update it.

danroth27 · 2018-04-05T17:52:53Z

The more I think about this less sure I am that having disposable transient services is a thing. You didn't create the service, so it's weird that you would be responsible for disposing it. @pakrym What's your thoughts on this?

SteveSandersonMS · 2018-04-05T18:10:23Z

@danroth27 That requirement is described in https://github.com/aspnet/Blazor/issues/464

pakrym · 2018-04-05T18:46:51Z

The more I think about this less sure I am that having disposable transient services is a thing. You didn't create the service, so it's weird that you would be responsible for disposing it.

You don't usually create singleton services, transients are created and should be disposed by DI container.

danroth27 · 2018-04-05T19:03:15Z

docs/dependency-injection.md

+* The applicable constructor must be *public*.
+* There must only be one applicable constructor. In case of an ambiguity, DI throws an exception.
+
+## Service lifetime


Services are created by the service provider, so they need to be disposed by the service provider. We need to address this as part of https://github.com/aspnet/Blazor/issues/464, but regardless I think this section should be removed as it contradicts that guidance. The content about implementing IDisposable on components should be covered in the components doc, not here.

danroth27

Looks good!

Add chapter about dependency injection in Blazor

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guardrex requested review from SteveSandersonMS and danroth27 April 3, 2018 15:24

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danroth27 requested a review from rynowak April 5, 2018 05:59

rstropek added 2 commits April 5, 2018 11:30

Update DI chapter

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Fix typo

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Minor grammatical updates

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guardrex requested a review from Rick-Anderson April 5, 2018 16:44

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guardrex added 3 commits April 5, 2018 12:46

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guardrex added 2 commits April 5, 2018 14:29

Remove service lifetime section

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guardrex removed the request for review from Rick-Anderson April 6, 2018 01:06

guardrex merged commit ed65c04 into aspnet:staging Apr 6, 2018

guardrex mentioned this pull request Apr 17, 2018

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Add chapter about dependency injection in Blazor #14

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		Blazor has [dependency injection (DI)](https://docs.microsoft.com/aspnet/core/fundamentals/dependency-injection) built-in. Blazor apps can use built-in services by having them injected into components. Blazor apps can also define custom services and make them available via DI.

		## What is dependency injection?


		Blazor's implementation of `System.IServiceProvider` obtains its services from an underlying [Microsoft.Extensions.DependencyInjection.IServiceCollection](https://docs.microsoft.com/dotnet/api/microsoft.extensions.dependencyinjection.iservicecollection).

		## Add services to DI


		## Dependency injection in services

		Complex services might require additional services. In the prior example, `DataAccess` might require Blazor's default service `HttpClient`. `@inject` or the `InjectAttribute` can't be used in services. Constructor injection must be used instead. Require services are added by adding parameters to the service's constructor. When dependency injection creates the service, it recognizes the services it requires in the constructor and provides them accordingly.


		## System services

		Blazor provides default services that are automatically added to the service collection of a Blazor app. The following table shows a list of the default services currently provided by Blazor.


		Blazor's DI system is responsible for supplying instances of services to components. DI also resolves dependencies recursively so that services themselves can depend on further services. DI is configured during startup of the app. An example is shown later in this topic.

		## Use of existing .NET mechanisms


		## Service lifetime

		Note that Blazor doesn't automatically dispose injected services that implement `IDisposable`. Components can implement `IDisposable`. Services are disposed when the user navigates away from the component.

Add chapter about dependency injection in Blazor #14

Add chapter about dependency injection in Blazor #14

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