CODEWITHSUNDEEP
c#.net-coredependency-injection
Donovan
Donovan

Reputation: 25

.NET Core Dependency Injection resolve question

In my startup of my WebApi project I've got the next code:

services.AddScoped<ICommandHandler<OpdrachtgeverToevoegenCommand>, OpdrachtgeverCommandHandler>();
services.AddScoped<ICommandHandler<OpdrachtgeverVerwijderenCommand>, OpdrachtgeverCommandHandler>();
services.AddScoped<ICommandHandler<OpdrachtgeverWijzigenCommand>, OpdrachtgeverCommandHandler>();

In my project I've got implementations of these interfaces.

Now I'm trying to find the correct implementation of this handler by using the command:

Here's the code that isn't completed yet:

public static ICommandHandler<ICommand> GetHandler(IServiceProvider serviceProvider, ICommand command)
{
    if (serviceProvider == null) throw new ArgumentNullException(nameof(serviceProvider));
    if (command == null) throw new ArgumentNullException(nameof(serviceProvider));

    var handler = serviceProvider.GetRequiredService(command.GetType());
    return serviceProvider.GetRequiredService(command.GetType()) as ICommandHandler<ICommand>;
}

I know that the command.GetType() returns the correct command, but how do I find the ICommandHandler<command.GetType()> implementation?

Upvotes: 1

Views: 342

Answers (1)

Tim Rogers
Tim Rogers

Reputation: 21713

You could dynamically make the type that you are looking up using MakeGenericType:

   var handlerType = typeof(ICommandHandler<>).MakeGenericType(command.GetType());
   return (ICommandHandler<ICommand>) serviceProvider.GetRequiredService(handlerType);

However, this will give you problems since I'm assuming that ICommandHandler<> is not covariant. You will not be able to cast it to ICommandHandler<ICommand>.

It's better to pass the type of command to the method as a generic argument.

public static ICommandHandler<TCommand> GetHandler<TCommand>(IServiceProvider serviceProvider, TCommand command)
{
    return serviceProvider.GetRequiredService<ICommandHandler<TCommand>>();
}

Upvotes: 2

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