Do we need interfaces for dependency injection?

Question

I have an ASP.NET Core application. The application has few helper classes that does some work. Each class has different signature method. I see lot of .net core examples on

Answer 1

I won't try to cover what others have already mentioned, using interfaces with DI will often be the best option. But it's worth mentioning that using object inheritance at times may provide another useful option. So for example:

public class Storage
 {
    public virtual Task Download(string file)
    {
    }
 }


public class DiskStorage: Storage
 {
    public override Task Download(string file)
    {
    }
 }

and registering it like so:

services.AddScoped();