CODEWITHSUNDEEP
asp.net-core.net-coredependency-injection
John
John

Reputation: 7049

Custom IServiceProviderFactory in ASP.NET Core

I wrote a custom IServiceProviderFactory and installed it in Program.cs of a new app like this:

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(new PropertyInjectingContainerFactory())
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

It does lead to the correct configure function in Startup.cs getting called:

   public void ConfigureContainer(PropertyInjectingContainerFactory.Builder builder)
   {
        builder.AddInjectAttribute<InjectDependencyAttribute>();
   }

However, my created container only ever resolves two services: IConfiguration and IHost.

Everything else is resolved by the default container apparantly (for instance a service like ILogger<T> on a controller). What do I do wrong?

Here's the code for my custom factory - and please understand that I probably should be using an existing third-party container, but I also want to understand how this all fits together.

public class PropertyInjectingContainerFactory : IServiceProviderFactory<PropertyInjectingContainerFactory.Builder>
{
    public Builder CreateBuilder(IServiceCollection services)
    {
        return new Builder(services);
    }

    public IServiceProvider CreateServiceProvider(Builder containerBuilder)
    {
        return containerBuilder.CreateServiceProvider();
    }

    public class Builder
    {
        internal readonly IServiceCollection services;

        internal List<Type> attributeTypes = new List<Type>();

        public Builder(IServiceCollection services)
        {
            this.services = services;
        }

        public Builder AddInjectAttribute<A>()
            where A : Attribute
        {
            attributeTypes.Add(typeof(A));

            return this;
        }

        public IServiceProvider CreateServiceProvider()
            => new PropertyInjectingServiceProvider(services.BuildServiceProvider(), attributeTypes.ToArray());
    }

    class PropertyInjectingServiceProvider : IServiceProvider
    {
        private readonly IServiceProvider services;
        private readonly Type[] injectAttributes;

        public PropertyInjectingServiceProvider(IServiceProvider services, Type[] injectAttributes)
        {
            this.services = services;
            this.injectAttributes = injectAttributes;
        }

        // This function is only called for `IConfiguration` and `IHost` - why?
        public object GetService(Type serviceType)
        {
            var service = services.GetService(serviceType);

            InjectProperties(service);

            return service;
        }

        private void InjectProperties(Object target)
        {
            var type = target.GetType();

            var candidateProperties = type.GetProperties(System.Reflection.BindingFlags.Public);

            var props = from p in candidateProperties
                        where injectAttributes.Any(a => p.GetCustomAttributes(a, true).Any())
                        select p;

            foreach (var prop in props)
            {
                prop.SetValue(target, services.GetService(prop.PropertyType));
            }
        }
    }
}

Upvotes: 6

Views: 2400

Answers (1)

Ricardo Peres
Ricardo Peres

Reputation: 14555

With some caveats, but it is possible. One of the problems is that WebApplication uses its own IServiceProviderFactory. Besides setting the IServiceProviderFactory for the host, you also need to replace the service provider with your own on each request (HttpContext.RequestServices and also the IServiceProviderFeature. I wrote a post and created some code which you can see here.

Upvotes: 0

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