Revised code base.

src/Volo.Abp.AspNetCore.MultiTenancy/Volo/Abp/AspNetCore/MultiTenancy/QueryStringTenantResolver.cs

@@ -1,10 +1,9 @@
 using Volo.Abp.MultiTenancy;
-using Volo.DependencyInjection;
 using Volo.ExtensionMethods.Collections.Generic;
 
 namespace Volo.Abp.AspNetCore.MultiTenancy
 {
-    public class QueryStringTenantResolver : ITenantResolver, ITransientDependency
+    public class QueryStringTenantResolver : ITenantResolver
     {
         public const string TenantIdKey = "__tenantId";
         

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

@@ -1,5 +1,4 @@
-using Microsoft.AspNetCore.Builder;
-using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection;
 using Volo.Abp.Modularity;
 
 namespace Volo.Abp.AspNetCore.Mvc
@@ -9,7 +8,6 @@ namespace Volo.Abp.AspNetCore.Mvc
     {
         public void ConfigureServices(IServiceCollection services)
         {
-            services.AddObjectAccessor<IApplicationBuilder>();
             services.AddAssemblyOf<AbpAspNetCoreMvcModule>();
         }
     }

src/Volo.Abp.AspNetCore/Volo/Abp/AspNetCore/AbpAspNetCoreModule.cs

@@ -10,10 +10,15 @@ namespace Volo.Abp.AspNetCore
     {
         public void ConfigureServices(IServiceCollection services)
         {
-            services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
+            AddAspNetServices(services);
 
             services.AddObjectAccessor<IApplicationBuilder>();
             services.AddAssemblyOf<AbpAspNetCoreModule>();
         }
+
+        private static void AddAspNetServices(IServiceCollection services)
+        {
+            services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
+        }
     }
 }

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

@@ -0,0 +1,26 @@
+using System;
+using System.Linq;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    public static class ServiceCollectionCommonExtensions
+    {
+        public static T GetSingletonInstanceOrNull<T>(this IServiceCollection services)
+        {
+            return (T)services
+                .FirstOrDefault(d => d.ServiceType == typeof(T))
+                ?.ImplementationInstance;
+        }
+
+        public static T GetSingletonInstance<T>(this IServiceCollection services)
+        {
+            var service = services.GetSingletonInstanceOrNull<T>();
+            if (service == null)
+            {
+                throw new InvalidOperationException("Could not find singleton service: " + typeof(T).AssemblyQualifiedName);
+            }
+
+            return service;
+        }
+    }
+}

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

@@ -4,24 +4,16 @@ using Volo.DependencyInjection;
 
 namespace Microsoft.Extensions.DependencyInjection
 {
-    public static class CommonServiceCollectionExtensions
+    public static class ServiceCollectionObjectAccessorExtensions
     {
-        public static T GetSingletonInstanceOrNull<T>(this IServiceCollection services)
+        public static ObjectAccessor<T> TryAddObjectAccessor<T>(this IServiceCollection services)
         {
-            return (T)services
-                .FirstOrDefault(d => d.ServiceType == typeof(T))
-                ?.ImplementationInstance;
-        }
-
-        public static T GetSingletonInstance<T>(this IServiceCollection services)
-        {
-            var service = services.GetSingletonInstanceOrNull<T>();
-            if (service == null)
+            if (services.Any(s => s.ServiceType == typeof(ObjectAccessor<T>)))
             {
-                throw new InvalidOperationException("Could not find singleton service: " + typeof(T).AssemblyQualifiedName);
+                return services.GetSingletonInstance<ObjectAccessor<T>>();
             }
 
-            return service;
+            return services.AddObjectAccessor<T>();
         }
 
         public static ObjectAccessor<T> AddObjectAccessor<T>(this IServiceCollection services)
@@ -36,6 +28,11 @@ namespace Microsoft.Extensions.DependencyInjection
 
         public static ObjectAccessor<T> AddObjectAccessor<T>(this IServiceCollection services, ObjectAccessor<T> accessor)
         {
+            if (services.Any(s => s.ServiceType == typeof(ObjectAccessor<T>)))
+            {
+                throw new Exception("An object accessor is registered before for type: " + typeof(T).AssemblyQualifiedName);
+            }
+
             services.AddSingleton(typeof(IObjectAccessor<T>), accessor);
             services.AddSingleton(typeof(ObjectAccessor<T>), accessor);