Can I use a dependency injection singleton in two different classes?

Question

I have an interface:

public interface Irepos 
{
    string somefunction();
}

Then the class I want to use:

public class repos : Irepos
{
    string somefunction()
    {
        return "function called";
    }
}

Registered as singleton in startup.cs:

services.AddSingleton<Irepos, repos>();

Now I can use it like this in my controller class:

public class controller 
{
    private readonly Irepos interfaceRepos;
    
    public ValuesController(Irepos reposInerface)
    {
        interfaceRepos = reposInerface;
    }

    interfaceRepos.somefunction();
}

Now my question is: can I use the same instance of the same repos class in a different class or different controller? Say:

public class AnotherController
{
    private readonly Irepos interfaceRepos;
        
    public ValuesController(Irepos reposInerface)
    {
        interfaceRepos = reposInerface;
    }
    
    interfaceRepos.somefunction();
}

Yes, that's how singletons work. DI will give the same `IRepos` instance (which is of type `repos`) to you for both controllers. — Martin Costello, Jul 09 '21 at 15:08
@David when i try it works, am asking if it's a good practice and exact why to use it or not , i was too afraid if there's something i don't know and somehow i get two instances of the class that'll be headache later to figure out . — thou_mayest, Jul 09 '21 at 15:16

score 0 · Accepted Answer · answered Jul 09 '21 at 17:09

By definition, only one instance of a singleton exists.

Your controllers can execute in parallel.

If the object in question is thread-safe (for example, it might contain lookup tables or other read-only values), it's reasonable and probably desirable to use a singleton.

If the object isn't thread-safe, scoped lifetime is likely to be the appropriate choice.

Can I use a dependency injection singleton in two different classes?

1 Answers1