Question: How to create instance of service that has constructor parameters.

[mhsimkin]

Environment: .NET 4.6.1 (Not Core)

I'm trying to use the new Microsoft.Extensions.DependencyInjections classes with .NET 4.6.1.

I have that has this signature:

public class RabbitMqConnection : IMessagingConnection`
{
     public RabbitMqConnection(ILogger<RabbitMqConnection> logger, string connectionString)
     {
     }
}

In my test harness, I'm creating an instance of the ServiceCollection, registering my interface and implementation.

[TestFixture]
    public class ConnectionTests
    {
        private readonly Uri AmqpUri = new Uri("aqmp://renscribe:Helium2@dwerecrq01.hq.bn-corp.com:5672/v.pds.ren.scribe");
        private readonly string ConnectionString =
            "host=dwerecrq01.hq.bn-corp.com;port=5672;virtualHost=v.pds.ren.scribe;requestedHeartbeat=30;prefetchcount=100;timeout=12" +
            "maxScribeLocalQueue=800;scribeMessageSerializeVersion=3;maxMessageSize=4194304;maxExceptionSize=4194304;getUserOnEveryMessage=true;";

        private static IServiceProvider _services;

        [SetUp]
        public void Setup()
        {
            var serviceCollection = new ServiceCollection();
            ConfigureServices(serviceCollection);
            _services = serviceCollection.BuildServiceProvider();
            var lf = _services.GetRequiredService<ILoggerFactory>();
            lf.AddConsole().AddDebug();
        }

        private void ConfigureServices(IServiceCollection serviceCollection)
        {
            serviceCollection.AddLogging();
            serviceCollection.AddTransient<IMessagingConnection, RabbitMqConnection>();
        }
        [Test]
        public void Should_correctly_parse_connection_string()
        {
            var connection =
                ActivatorUtilities.CreateInstance<IMessagingConnection>(_services, ConnectionString );
                //_services.GetRequiredService<IMessagingConnection>();

            var logger = _services.GetRequiredService<ILogger<ConnectionTests>>();

            using (logger.BeginScope($"=>{nameof(Should_correctly_parse_connection_string)}"))
            {
                logger.LogInformation("Test starting");
                logger.LogInformation("Test completed");
            }
        }
    }

The call to ActivatorUtilities.CreateInstance fails with the error:

A suitable constructor for type 'bn.pds.tools.Messaging.IMessagingConnection' could not be located. Ensure the type is concrete and services are registered for all parameters of a public constructor.

If I remove the string parameter to the constructor, and use _services.GetRequiredService<>(), everything works as expected.

How can I create an instance of a service that requires additional parameters for the constructor?

Thanks

marc

[mhsimkin]

If there are examples, documentation, kb, wiki pages available that answer my questions, please point me in the correct direction.

Thanks

[pranavkm]

You need to add ILogger<T> to the container. See https://github.com/aspnet/Logging/blob/dev/src/Microsoft.Extensions.Logging/LoggingServiceCollectionExtensions.cs#L28

[mhsimkin]

Hi, thank you for your response. I tested that approach, I still get the same error. I also changed my constructor to expect an ILoggerFactory instead of an ILogger, the same issue.

Also, if I just have my constructor expect an ILogger, and use the IServiceProvider::GetRequiredService method, my object is created, and the constructor is called.

Further, this call in my code resolves file when a Logger<> is registered:

var logger = _services.GetRequiredService<ILogger<ConnectionTests>>();

[pranavkm]

Sorry, I just noticed your AddLogging statement. That said, the issue is here that ActivatorUtilities.CreateInstance<TVal> works similar to how Activator.CreateInstance works - it creates an instance of TVal by filling in values passed in or from the service container when there isn't an equivalent argument. In this case, you have to do Activator.CreateInstance<RabbitMqConnection>() as opposed to Activator.CreateInstance<IMessageConnection>().

[mhsimkin]

thanks. that resolved the issue and made me realize, I have a design problem.