Unity: The current type is an interface and cannot be constructed

Question

Got below code to start with

public interface IDataContextAsync : IDataContext
{
    Task SaveChangesAsync(CancellationToken cancellationToken);
          


        

Answer 1

Your service locator that is doing the resolving (after your constructor asks for IDataContextAsync) is probably trying to resolve like this:

Current.Resolve<IDataContextAsync>()

when it needs to resolve like this

Current.Resolve<IDataContextAsync>("DB1Context");

and there wouldn't be any extra logic built into it for it to know that.

If you want to conditionally resolve you could use an injection factory:

   public static class Factory
   {
        public static IDataContextAsync GetDataContext()
        {
            if (DateTime.Now.Hour > 10)
            {
                return new DB1Context();
            }
            else
            {
                return new DB2Context();
            }
        }
    }

..and register IDataContextAsync like this:

Current.RegisterType<IDataContextAsync>(new InjectionFactory(c => Factory.GetDataContext()));

Since it takes a delegate you don't necessarily need the static class / method and could do it inline.