More examples of Singleton, Transient and Scoped Injection Dependency

[zabpetrus]

Type of issue

Thank you

Description

I need to use two types of constructors: one for the application and another for the tester. So, I need to master the subject of dependency injection to avoid the aggregation error, which indicates circular references. I tried to implement the example given, but it didn't work. And there's just one example... What changes should be made to the classes to be able to do dependency injection? What should be added? what should be removed? Help me, because I'm using Moq and I can't remove the constructor with injection! I could give two examples: normal mode and using transient, scoped and singleton and teach how the student can migrate the modes to make it work. Thanks

Page URL

https://learn.microsoft.com/en-us/dotnet/core/extensions/dependency-injection

Content source URL

https://github.com/dotnet/docs/blob/main/docs/core/extensions/dependency-injection.md

Document Version Independent Id

cc5f00d0-fb50-1229-8fa2-e66b1f45b284

Article author

@IEvangelist

Metadata

• ID: 8fd55089-b683-2202-6641-c7b61a132f14
• Service: dotnet-fundamentals

[IEvangelist]

Show me what you're trying to do? If you could provide the code that you have, I might be able to help.

[zabpetrus]

Hello again! I am facing a runtime issue when trying to instantiate an implementation for the 'API.Application.Interfaces.IContatoAppService' interface. The specific error is as follows: System.ArgumentException: 'Cannot instantiate implementation type 'API.Application.Interfaces.IContatoAppService' for service type 'API.Application.Interfaces.IContatoAppService'.' In the Builder I called: builder.Services.AddScoped<IContatoAppService, IContatoAppService>() and I tried other ways too: they all threw an exception. I'm finding it difficult to solve this problem, as it's not clear where exactly the error is (Sorry for the inconvenience, but I've got a project in progress, and from what I know, dependency injection works with Scoped, Singleton and others - but there is another way, which I couldn't identify, but which generates the error ) It would be nice if you could provide more detailed error messages or suggestions about what could be causing this problem, as the error is pointed out in the builder (very generic). Thank you in advance for your assistance! Em qua., 29 de mai. de 2024 às 16:24, David Pine ***@***.***> escreveu:

…

Show me what you're trying to do? If you could provide the code that you have, I might be able to help. — Reply to this email directly, view it on GitHub <#41082 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQ7OS2J6SBPMZV2FREP2MCLZEYTP7AVCNFSM6AAAAABIKCHCPCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCMZYGEYTANBRG4> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[IEvangelist]

Got it, thank you for the added context, that's very helpful! Ok, I see the issue. When you call:

builder.Services.AddScoped<IContatoAppService, IContatoAppService>();

That's registering a scoped IContatoAppService type with a corresponding implementation of the interface. That's not going to work, since it cannot instantiate an interface, nothing can. Instead, you need to register (or map) the corresponding implementation.

Consider this:

builder.Services.AddScoped<IContatoAppService, DefaultContatoAppService>();

In this example, the implemenation is the DefaultContatoAppService. It has to be defined somewhere:

public class DefaultContatoAppService : IContatoAppService
{
    // TODO: Implement members.
}

Does that make more sense now? Then for unit tests, you could mock the interface and use that.

[zabpetrus]

Thank you for responding. I think you'd better see my project to get an idea. I put AddScoped on (and tried the others) but it was the same thing as nothing. I don't know... I've been trying for weeks. It might help me know where I'm going wrong! https://github.com/zabpetrus/bazartemtudo/tree/main/BazarTemTudo Actually... trying to make dependency injection work. Until now, I'm forced to use new()... Thanks! Em qua., 29 de mai. de 2024 às 20:09, David Pine ***@***.***> escreveu:

…

Got it, thank you for the added context, that's very helpful! Ok, I see the issue. When you call: builder.Services.AddScoped<IContatoAppService, IContatoAppService>(); That's registering a scoped IContatoAppService type with a corresponding implementation of the interface. That's not going to work, since it cannot instantiate an interface, nothing can. Instead, you need to register (or map) the corresponding implementation. Consider this: builder.Services.AddScoped<IContatoAppService, DefaultContatoAppService>(); In this example, the implemenation is the DefaultContatoAppService. It has to be defined somewhere: public class DefaultContatoAppService : IContatoAppService{ // TODO: Implement members.} Does that make more sense now? Then for unit tests, you could mock the interface and use that. — Reply to this email directly, view it on GitHub <#41082 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQ7OS2NGGTQK724LKJTOWGLZEZNZBAVCNFSM6AAAAABIKCHCPCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCMZYGM4TMNZQGU> . You are receiving this because you authored the thread.Message ID: ***@***.***>