Optional dependency @inject for Blazor

[stefanloerwald]

Is your feature request related to a problem? Please describe.

In some situations, services can be optional. For regular classes we can write

public class Foo
{
    public Foo(IService service = null) {} // optional dependency on IService
}

For @inject and [Inject], there's no such equivalence.

Describe the solution you'd like

I'd love to see a parameter to the Inject attribute that allows to mark a dependency as optional, e.g. [Inject(Optional = true)]. The @inject directive could be extended to make @inject IService Service = null valid and equivalent with [Inject(Optional = true)] IService Service {get;set;} which (as far as I can see) would not break any existing code as it would be a syntax error so far.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[richbryant]

Honestly, it would be nicer to be able to do "normal" constructor injection using codebehind mycomponent.razor.cs classes. Then you can have optional injection if you need it without faffing around with @ directives.

[stefanloerwald]

Honestly, I don't mind which way it works, as long as I can make dependencies optional: whether allowing DI constructors or adding support for optional dependencies with directives has the smaller impact on the framework, I can't say.

[richbryant]

let's just say, parameter injection is nasty. And the @ directive is really just parameter injection in disguise. I'm not saying do away with it, some people like code and markup in the same file and who am I to judge? But where you have a complex requirement, there's a real benefit to going down the standard path.

[Liero]

@stefanloerwald:

meanwhile, can you use this?

@inject IServiceProvider ServiceProvider

@code 
{
    IService _service;

    protected override void OnInitialized() 
    {
        _service = ServiceProvider.GetService<IService>();
    }
}

[stefanloerwald]

Thank you @Liero for the suggestion. That code absolutely works and is a nice workaround. I still hope the feature will be added directly into Blazor.

[andersson09]

Any update on this?

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We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
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