How can I use/inject a service in a "normal" c# class like in Blazor @inject ClassName classObject

Question

I have a Blazor Project, in the Program.cs(formaly aka Startup.cs) I added a service

            builder.Services.AddSingleton<Models.UserVisit>();
        

I can use/access that service on a razor/blazor page like this :

       @inject Models.UserVisit userVisitObj

(UserVisit is a "normal" C# .cs Class in the folder Models)

What I don't know is how can I use this "userVisitObj" in a normal C# Class that does not have a razorpage (where I would use the @inject)?

How do I use that in here (normal C# Class in the same project but without a blazor/razor-componentpage):

public class UserModel
{
    [BsonId]
    public Guid Id { get; set; }
    public CultureInfo UserCultureInfo { get; set; }
    ...

    public UserModel()
    {
        [Inject]
        Models.UserVisit userVisitObj;   // THAT DOESN'T WORK -- ERROR
    }
}

I hope I could make my question somewhat clear (please be kind I'm still a beginner).

Retardation

Generally you would just follow standard dependency injection. So in your case the UserModel() constructor would take in Models.UserVisit as a parameter. But how that is resolved depends on how/where you're constructing the UserModel class – Notability

@Notability can you elaborate on the last sentence? I find this works but it seems like magic and would like to understand it better. If I try to new() such a class it complains about missing parameter; but objects that are constructed by the framework seem to be able to fill in the parameter from somewhere. – Hoagland

@Hoagland same thing for me, any new() instancation complains about the missing parameter, did you ever figure it out? – Iceblink

@Iceblink Nope, lol – Hoagland

Answer 1

You can use constructor injection as follows:

private readonly Models.UserVisit _userVisitObj
public UserModel(Models.UserVisit userVisitObj)
{
      _userVisitObj = userVisitObj;
 
}

Note that this is applicable to normal C# classes.

If your class is a component class, you need to use the Inject attribute with a public property, as for instance:

[Inject]
public Models.UserVisit UserVisit {get; set;}

Hope this helps...

Plunger

I have tried using the [Inject] version in a normal C# class (not a component class), however the property always reads as null, is something else needed to make it go and get the service? – Hoagland

in a normal class use 'constructor injection'. The first part of the answere (private field ...). – Retardation