Refactored.

src/Volo.Abp.ApplicationContracts/Volo/Abp/Application/Services/IApplicationService.cs

@@ -3,7 +3,7 @@
 namespace Volo.Abp.Application.Services
 {
     /// <summary>
-    /// This interface must be implemented by all application services to identify them by convention.
+    /// This interface must be implemented by all application services to register and identify them by convention.
     /// </summary>
     public interface IApplicationService : ITransientDependency
     {

src/Volo.Abp.AspNetCore.Mvc/Volo/Abp/AspNetCore/Mvc/AbpController.cs

@@ -1,8 +1,9 @@
 using Microsoft.AspNetCore.Mvc;
+using Volo.DependencyInjection;
 
 namespace Volo.Abp.AspNetCore.Mvc
 {
-    public abstract class AbpController : Controller
+    public abstract class AbpController : Controller, ITransientDependency
     {
 
     }

src/Volo.Abp.AspNetCore/Microsoft/AspNetCore/Builder/AbpApplicationBuilderExtensions.cs

@@ -1,4 +1,6 @@
-using Microsoft.Extensions.DependencyInjection;
+using JetBrains.Annotations;
+using Microsoft.Extensions.DependencyInjection;
+using Volo;
 using Volo.Abp;
 using Volo.DependencyInjection;
 
@@ -6,8 +8,10 @@ namespace Microsoft.AspNetCore.Builder
 {
     public static class AbpApplicationBuilderExtensions
     {
-        public static void InitializeApplication(this IApplicationBuilder app)
+        public static void InitializeApplication([NotNull] this IApplicationBuilder app)
         {
+            Check.NotNull(app, nameof(app));
+
             app.ApplicationServices.GetRequiredService<ObjectAccessor<IApplicationBuilder>>().Object = app;
             app.ApplicationServices.GetRequiredService<AbpApplication>().Initialize(app.ApplicationServices);
         }

src/Volo.DependencyInjection/Microsoft/Extensions/DependencyInjection/ServiceCollectionRegistrationExtensions.cs

@@ -11,33 +11,35 @@ namespace Microsoft.Extensions.DependencyInjection
     public static class ServiceCollectionRegistrationExtensions
     {
         //TODO: Check if assembly/type is added before or add TryAdd versions of them?
-        //TODO: Return IServiceCollection from all methods
+        //TODO: When to use Add, when to use TryAdd? We may think to add conventional interfaces to indicate and attributes to override them.
 
-        public static void AddAssemblyOf<T>(this IServiceCollection services)
+        public static IServiceCollection AddAssemblyOf<T>(this IServiceCollection services)
         {
-            services.AddAssembly(typeof(T).GetTypeInfo().Assembly);
+            return services.AddAssembly(typeof(T).GetTypeInfo().Assembly);
         }
 
-        public static void AddAssembly(this IServiceCollection services, Assembly assembly)
+        public static IServiceCollection AddAssembly(this IServiceCollection services, Assembly assembly)
         {
             var types = AssemblyHelper.GetAllTypes(assembly).Where(t =>
             {
                 var typeInfo = t.GetTypeInfo();
-                return typeInfo.IsClass && !typeInfo.IsAbstract && !typeInfo.IsGenericType && !typeInfo.IsDefined(typeof(DisableAutoDependencyInjectionRegistrationAttribute));
+                return typeInfo.IsClass && !typeInfo.IsAbstract && !typeInfo.IsGenericType && !typeInfo.IsDefined(typeof(SkipAutoRegistrationAttribute));
             });
-            
-            services.AddTypes(types.ToArray());
+
+            return services.AddTypes(types.ToArray());
         }
 
-        public static void AddTypes(this IServiceCollection services, params Type[] types)
+        public static IServiceCollection AddTypes(this IServiceCollection services, params Type[] types)
         {
             foreach (var type in types)
             {
                 services.AddType(type);
             }
+
+            return services;
         }
 
-        public static void AddType(this IServiceCollection services, Type type)
+        public static IServiceCollection AddType(this IServiceCollection services, Type type)
         {
             //TODO: Make this code extensible, so we can add other conventions!
 
@@ -58,9 +60,11 @@ namespace Microsoft.Extensions.DependencyInjection
                     services.AddScoped(serviceType, type);
                 }
             }
+
+            return services;
         }
-        
-        private static List<Type> FindServiceTypes(Type type)
+
+        private static IEnumerable<Type> FindServiceTypes(Type type)
         {
             var customExposedServices = type.GetTypeInfo().GetCustomAttributes().OfType<IExposedServiceTypesProvider>().SelectMany(p => p.GetExposedServiceTypes()).ToList();
             if (customExposedServices.Any())
@@ -68,9 +72,7 @@ namespace Microsoft.Extensions.DependencyInjection
                 return customExposedServices;
             }
 
-            var serviceTypes = new List<Type>();
-
-            serviceTypes.Add(type);
+            var serviceTypes = new List<Type> { type };
 
             foreach (var interfaceType in type.GetTypeInfo().GetInterfaces())
             {

src/Volo.DependencyInjection/Volo/DependencyInjection/DisableAutoDependencyInjectionRegistrationAttribute.cs

@@ -1,9 +0,0 @@
-using System;
-
-namespace Volo.DependencyInjection
-{
-    public class DisableAutoDependencyInjectionRegistrationAttribute : Attribute
-    {
-
-    }
-}

src/Volo.DependencyInjection/Volo/DependencyInjection/ExposeServicesAttribute.cs

@@ -8,7 +8,7 @@ namespace Volo.DependencyInjection
 
         public ExposeServicesAttribute(params Type[] exposedServiceTypes)
         {
-            ExposedServiceTypes = exposedServiceTypes;
+            ExposedServiceTypes = exposedServiceTypes ?? new Type[];
         }
 
         public Type[] GetExposedServiceTypes()

src/Volo.DependencyInjection/Volo/DependencyInjection/SkipAutoRegistrationAttribute.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace Volo.DependencyInjection
+{
+    public class SkipAutoRegistrationAttribute : Attribute
+    {
+
+    }
+}