I've run into a bit of trouble trying to use dependency injection and need help.
I have a service IService
that is implemented a few different ways in my application.
ServiceA : IService { public ServiceA(IDependencyA A, IDependency B) {...} }
ServiceB : IService { public ServiceB(IDependencyA A, IDependency B) {...} }
ServiceC : IService { public ServiceC(IService serviceA, IService serviceB) {...} }
In my startup.cs
file, I will pick which one to use based on a parameter in my configuration file. Something like this:
var service = Configuration["AppConfig:Service:ID"];
switch(service) {
case "A":
services.AddTransient<IService, ServiceA>();
case "B":
services.AddTransient<IService, ServiceB>();
case "C":
// ??
}
I am able to create and use service A and service B very easily. I inject their dependencies A and B before hand and they get created just fine. The problem is with the third service. I need to inject the two other services into it. My question is: what is the best to do this?
Is there a way I can create concrete implementations of service A and B but somehow use the injected dependency A and B in their constructor? Do I have to mess around with the interfaces to get this to work? Maybe I have to change the constructor of ServiceC to take in concrete implementations of A & B?
Updated: don't know if it's the best solution, but I ended up doing the following to get it to work.
...
case "C":
services.AddTransient<ServiceA>();
services.AddTransient<ServiceB>();
services.AddTransient<IService>(s =>
new ServiceC(
s.GetService<ServiceA>(),
s.GetService<ServiceB>()
));
Another alternative. Introduce another interface, so you can register the both ServiceC
and it's dependencies at the same time, without any ambiguity or circular references.
interface IService {}
interface IServiceImpl : IService {}
ServiceA : IServiceImpl { public ServiceA(IDependencyA A, IDependency B) {...} }
ServiceB : IServiceImpl { public ServiceB(IDependencyA A, IDependency B) {...} }
ServiceC : IService { public ServiceC(IEnumerable<IServiceImpl> services) {...} }
services.AddTransient<IServiceImpl, ServiceA>();
services.AddTransient<IServiceImpl, ServiceB>();
services.AddTransient<IService, ServiceC>();
There must be a better explanation for having such dependencies.
Microsoft.Extensions.DependencyInjection does not provide named registrations like other IoC containers ie Castle.Windsor.
There is a way you can still register ServiceC with instances of A and B
services.AddTransient<ServiceA>();
services.AddTransient<ServiceB>();
services.AddTransient<IService>(serviceProvider => {
return new ServiceC((IService)serviceProvider.GetRequiredService(typeof(ServiceA)), (IService)serviceProvider.GetRequiredService(typeof(ServiceB)));
});
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