Refactor and cleanup tag helper creation.

* Moved instantiation of tag helpers into DefaultTagHelperActivator.
* Introduced ITagHelperFactory for handling the setup of new tag helper instances.

src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs

@@ -130,6 +130,7 @@ namespace Microsoft.Extensions.DependencyInjection
 
             // Only want one ITagHelperActivator so it can cache Type activation information. Types won't conflict.
             services.TryAddSingleton<ITagHelperActivator, DefaultTagHelperActivator>();
+            services.TryAddSingleton<ITagHelperFactory, DefaultTagHelperFactory>();
 
             // Consumed by the Cache tag helper to cache results across the lifetime of the application.
             services.TryAddSingleton<IMemoryCache, MemoryCache>();

src/Microsoft.AspNetCore.Mvc.Razor/ITagHelperActivator.cs

@@ -7,16 +7,16 @@ using Microsoft.AspNetCore.Razor.TagHelpers;
 namespace Microsoft.AspNetCore.Mvc.Razor
 {
     /// <summary>
-    /// Provides methods to activate properties on a <see cref="ITagHelper"/> instance.
+    /// Provides methods to create a tag helper.
     /// </summary>
     public interface ITagHelperActivator
     {
         /// <summary>
-        /// When implemented in a type, activates an instantiated <see cref="ITagHelper"/>.
+        /// Creates an <see cref="ITagHelper"/>.
         /// </summary>
         /// <typeparam name="TTagHelper">The <see cref="ITagHelper"/> type.</typeparam>
-        /// <param name="tagHelper">The <typeparamref name="TTagHelper"/> to activate.</param>
         /// <param name="context">The <see cref="ViewContext"/> for the executing view.</param>
-        void Activate<TTagHelper>(TTagHelper tagHelper, ViewContext context) where TTagHelper : ITagHelper;
+        /// <returns>The tag helper.</returns>
+        TTagHelper Create<TTagHelper>(ViewContext context) where TTagHelper : ITagHelper;
     }
 }

src/Microsoft.AspNetCore.Mvc.Razor/ITagHelperFactory.cs

@@ -0,0 +1,21 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace Microsoft.AspNetCore.Mvc.Razor
+{
+    /// <summary>
+    /// Provides methods to create and initialize tag helpers.
+    /// </summary>
+    public interface ITagHelperFactory
+    {
+        /// <summary>
+        /// Creates a new tag helper for the specified <paramref name="context"/>.
+        /// </summary>
+        /// <param name="context"><see cref="ViewContext"/> for the executing view.</param>
+        /// <returns>The tag helper.</returns>
+        TTagHelper CreateTagHelper<TTagHelper>(ViewContext context) where TTagHelper : ITagHelper;
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor/Internal/DefaultTagHelperActivator.cs

@@ -2,79 +2,45 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Concurrent;
+using Microsoft.AspNetCore.Mvc.Internal;
-using System.Collections.Generic;
-using System.Reflection;
 using Microsoft.AspNetCore.Mvc.Rendering;
-using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Razor.TagHelpers;
-using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Default implementation of <see cref="ITagHelperActivator"/>.
+    /// </summary>
     public class DefaultTagHelperActivator : ITagHelperActivator
     {
-        private readonly ConcurrentDictionary<Type, PropertyActivator<ViewContext>[]> _injectActions;
+        private readonly ITypeActivatorCache _typeActivatorCache;
-        private readonly Func<Type, PropertyActivator<ViewContext>[]> _getPropertiesToActivate;
 
         /// <summary>
         /// Instantiates a new <see cref="DefaultTagHelperActivator"/> instance.
         /// </summary>
-        public DefaultTagHelperActivator()
+        /// <param name="typeActivatorCache">The <see cref="ITypeActivatorCache"/>.</param>
+        public DefaultTagHelperActivator(ITypeActivatorCache typeActivatorCache)
         {
-            _injectActions = new ConcurrentDictionary<Type, PropertyActivator<ViewContext>[]>();
+            if (typeActivatorCache == null)
-            _getPropertiesToActivate = type =>
+            {
-                PropertyActivator<ViewContext>.GetPropertiesToActivate(
+                throw new ArgumentNullException(nameof(typeActivatorCache));
-                    type,
+            }
-                    typeof(ViewContextAttribute),
+
-                    CreateActivateInfo);
+            _typeActivatorCache = typeActivatorCache;
         }
 
         /// <inheritdoc />
-        public void Activate<TTagHelper>(TTagHelper tagHelper, ViewContext context)
+        public TTagHelper Create<TTagHelper>(ViewContext context)
             where TTagHelper : ITagHelper
         {
-            if (tagHelper == null)
-            {
-                throw new ArgumentNullException(nameof(tagHelper));
-            }
-
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var propertiesToActivate = _injectActions.GetOrAdd(
+            return _typeActivatorCache.CreateInstance<TTagHelper>(
-                tagHelper.GetType(),
+                context.HttpContext.RequestServices,
-                _getPropertiesToActivate);
+                typeof(TTagHelper));
-
-            for (var i = 0; i < propertiesToActivate.Length; i++)
-            {
-                var activateInfo = propertiesToActivate[i];
-                activateInfo.Activate(tagHelper, context);
-            }
-
-            InitializeTagHelper(tagHelper, context);
-        }
-
-        private static void InitializeTagHelper<TTagHelper>(TTagHelper tagHelper, ViewContext context)
-            where TTagHelper : ITagHelper
-        {
-            // Run any tag helper initializers in the container
-            var serviceProvider = context.HttpContext.RequestServices;
-            var initializers = serviceProvider.GetService<IEnumerable<ITagHelperInitializer<TTagHelper>>>();
-
-            foreach (var initializer in initializers)
-            {
-                initializer.Initialize(tagHelper, context);
-            }
-        }
-
-        private static PropertyActivator<ViewContext> CreateActivateInfo(PropertyInfo property)
-        {
-            return new PropertyActivator<ViewContext>(property, viewContext => viewContext);
         }
     }
 }

src/Microsoft.AspNetCore.Mvc.Razor/Internal/DefaultTagHelperFactory.cs

@@ -0,0 +1,92 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Reflection;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Internal;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.Internal
+{
+    /// <summary>
+    /// Default implementation for <see cref="ITagHelperFactory"/>.
+    /// </summary>
+    public class DefaultTagHelperFactory : ITagHelperFactory
+    {
+        private readonly ITagHelperActivator _activator;
+        private readonly ConcurrentDictionary<Type, PropertyActivator<ViewContext>[]> _injectActions;
+        private readonly Func<Type, PropertyActivator<ViewContext>[]> _getPropertiesToActivate;
+        private static readonly Func<PropertyInfo, PropertyActivator<ViewContext>> _createActivateInfo = CreateActivateInfo;
+
+        /// <summary>
+        /// Initializes a new <see cref="DefaultTagHelperFactory"/> instance.
+        /// </summary>
+        /// <param name="activator">
+        /// The <see cref="ITagHelperActivator"/> used to create tag helper instances.
+        /// </param>
+        public DefaultTagHelperFactory(ITagHelperActivator activator)
+        {
+            if (activator == null)
+            {
+                throw new ArgumentNullException(nameof(activator));
+            }
+
+            _activator = activator;
+            _injectActions = new ConcurrentDictionary<Type, PropertyActivator<ViewContext>[]>();
+            _getPropertiesToActivate = type =>
+                PropertyActivator<ViewContext>.GetPropertiesToActivate(
+                    type,
+                    typeof(ViewContextAttribute),
+                    _createActivateInfo);
+        }
+
+        /// <inheritdoc />
+        public TTagHelper CreateTagHelper<TTagHelper>(ViewContext context)
+            where TTagHelper : ITagHelper
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            var tagHelper = _activator.Create<TTagHelper>(context);
+
+            var propertiesToActivate = _injectActions.GetOrAdd(
+                tagHelper.GetType(),
+                _getPropertiesToActivate);
+
+            for (var i = 0; i < propertiesToActivate.Length; i++)
+            {
+                var activateInfo = propertiesToActivate[i];
+                activateInfo.Activate(tagHelper, context);
+            }
+
+            InitializeTagHelper(tagHelper, context);
+
+            return tagHelper;
+        }
+
+        private static void InitializeTagHelper<TTagHelper>(TTagHelper tagHelper, ViewContext context)
+            where TTagHelper : ITagHelper
+        {
+            // Run any tag helper initializers in the container
+            var serviceProvider = context.HttpContext.RequestServices;
+            var initializers = serviceProvider.GetService<IEnumerable<ITagHelperInitializer<TTagHelper>>>();
+
+            foreach (var initializer in initializers)
+            {
+                initializer.Initialize(tagHelper, context);
+            }
+        }
+
+        private static PropertyActivator<ViewContext> CreateActivateInfo(PropertyInfo property)
+        {
+            return new PropertyActivator<ViewContext>(property, viewContext => viewContext);
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor/RazorPage.cs

@@ -32,8 +32,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         private readonly HashSet<string> _renderedSections = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
         private readonly Stack<TagHelperScopeInfo> _tagHelperScopes = new Stack<TagHelperScopeInfo>();
         private IUrlHelper _urlHelper;
-        private ITagHelperActivator _tagHelperActivator;
+        private ITagHelperFactory _tagHelperFactory;
-        private ITypeActivatorCache _typeActivatorCache;
         private bool _renderedBody;
         private AttributeInfo _attributeInfo;
         private TagHelperAttributeInfo _tagHelperAttributeInfo;
@@ -122,31 +121,17 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         /// <inheritdoc />
         public abstract Task ExecuteAsync();
 
-        private ITagHelperActivator TagHelperActivator
+        private ITagHelperFactory TagHelperFactory
         {
             get
             {
-                if (_tagHelperActivator == null)
+                if (_tagHelperFactory == null)
                 {
                     var services = ViewContext.HttpContext.RequestServices;
-                    _tagHelperActivator = services.GetRequiredService<ITagHelperActivator>();
+                    _tagHelperFactory = services.GetRequiredService<ITagHelperFactory>();
                 }
 
-                return _tagHelperActivator;
+                return _tagHelperFactory;
-            }
-        }
-
-        private ITypeActivatorCache TypeActivatorCache
-        {
-            get
-            {
-                if (_typeActivatorCache == null)
-                {
-                    var services = ViewContext.HttpContext.RequestServices;
-                    _typeActivatorCache = services.GetRequiredService<ITypeActivatorCache>();
-                }
-
-                return _typeActivatorCache;
             }
         }
 
@@ -192,13 +177,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         /// </remarks>
         public TTagHelper CreateTagHelper<TTagHelper>() where TTagHelper : ITagHelper
         {
-            var tagHelper = TypeActivatorCache.CreateInstance<TTagHelper>(
+            return TagHelperFactory.CreateTagHelper<TTagHelper>(ViewContext);
-                ViewContext.HttpContext.RequestServices,
-                typeof(TTagHelper));
-
-            TagHelperActivator.Activate(tagHelper, ViewContext);
-
-            return tagHelper;
         }
 
         /// <summary>

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/DefaultTagHelperActivatorTest.cs

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System;
 using System.IO;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
@@ -20,125 +19,24 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 {
     public class DefaultTagHelperActivatorTest
     {
-        [Theory]
+        [Fact]
-        [InlineData("test", 100)]
+        public void CreateTagHelper_InitializesTagHelpers()
-        [InlineData(null, -1)]
-        public void Activate_InitializesTagHelpers(string name, int number)
         {
             // Arrange
-            var services = new ServiceCollection();
+            var httpContext = new DefaultHttpContext()
-            var builder = new MvcCoreBuilder(services);
-            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
             {
-                h.Name = name;
+                RequestServices = new ServiceCollection().BuildServiceProvider()
-                h.Number = number;
+            };
-                h.ViewDataValue = vc.ViewData["TestData"];
-            });
-            var httpContext = MakeHttpContext(services.BuildServiceProvider());
             var viewContext = MakeViewContext(httpContext);
             var viewDataValue = new object();
             viewContext.ViewData.Add("TestData", viewDataValue);
-            var activator = new DefaultTagHelperActivator();
+            var activator = new DefaultTagHelperActivator(new TypeActivatorCache());
-            var helper = new TestTagHelper();
 
             // Act
-            activator.Activate(helper, viewContext);
+            var helper = activator.Create<TestTagHelper>(viewContext);
 
             // Assert
-            Assert.Equal(name, helper.Name);
+            Assert.NotNull(helper);
-            Assert.Equal(number, helper.Number);
-            Assert.Same(viewDataValue, helper.ViewDataValue);
-        }
-
-        [Fact]
-        public void Activate_InitializesTagHelpersAfterActivatingProperties()
-        {
-            // Arrange
-            var services = new ServiceCollection();
-            var builder = new MvcCoreBuilder(services);
-            builder.InitializeTagHelper<TestTagHelper>((h, _) => h.ViewContext = MakeViewContext(MakeHttpContext()));
-            var httpContext = MakeHttpContext(services.BuildServiceProvider());
-            var viewContext = MakeViewContext(httpContext);
-            var activator = new DefaultTagHelperActivator();
-            var helper = new TestTagHelper();
-
-            // Act
-            activator.Activate(helper, viewContext);
-
-            // Assert
-            Assert.NotSame(viewContext, helper.ViewContext);
-        }
-
-        [Fact]
-        public void Activate_InitializesTagHelpersWithMultipleInitializers()
-        {
-            // Arrange
-            var services = new ServiceCollection();
-            var builder = new MvcCoreBuilder(services);
-            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
-            {
-                h.Name = "Test 1";
-                h.Number = 100;
-            });
-            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
-            {
-                h.Name += ", Test 2";
-                h.Number += 100;
-            });
-            var httpContext = MakeHttpContext(services.BuildServiceProvider());
-            var viewContext = MakeViewContext(httpContext);
-            var activator = new DefaultTagHelperActivator();
-            var helper = new TestTagHelper();
-
-            // Act
-            activator.Activate(helper, viewContext);
-
-            // Assert
-            Assert.Equal("Test 1, Test 2", helper.Name);
-            Assert.Equal(200, helper.Number);
-        }
-
-        [Fact]
-        public void Activate_InitializesTagHelpersWithCorrectInitializers()
-        {
-            // Arrange
-            var services = new ServiceCollection();
-            var builder = new MvcCoreBuilder(services);
-            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
-            {
-                h.Name = "Test 1";
-                h.Number = 100;
-            });
-            builder.InitializeTagHelper<AnotherTestTagHelper>((h, vc) =>
-            {
-                h.Name = "Test 2";
-                h.Number = 102;
-            });
-            var httpContext = MakeHttpContext(services.BuildServiceProvider());
-            var viewContext = MakeViewContext(httpContext);
-            var activator = new DefaultTagHelperActivator();
-            var testTagHelper = new TestTagHelper();
-            var anotherTestTagHelper = new AnotherTestTagHelper();
-
-            // Act
-            activator.Activate(testTagHelper, viewContext);
-            activator.Activate(anotherTestTagHelper, viewContext);
-
-            // Assert
-            Assert.Equal("Test 1", testTagHelper.Name);
-            Assert.Equal(100, testTagHelper.Number);
-            Assert.Equal("Test 2", anotherTestTagHelper.Name);
-            Assert.Equal(102, anotherTestTagHelper.Number);
-        }
-
-        private static HttpContext MakeHttpContext(IServiceProvider services = null)
-        {
-            var httpContext = new DefaultHttpContext();
-            if (services != null)
-            {
-                httpContext.RequestServices = services;
-            }
-            return httpContext;
         }
 
         private static ViewContext MakeViewContext(HttpContext httpContext)

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/DefaultTagHelperFactoryTest.cs

@@ -0,0 +1,197 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.IO;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Internal;
+using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.Internal;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewEngines;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.Internal
+{
+    public class DefaultTagHelperFactoryTest
+    {
+        [Theory]
+        [InlineData("test", 100)]
+        [InlineData(null, -1)]
+        public void CreateTagHelper_InitializesTagHelpers(string name, int number)
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            var builder = new MvcCoreBuilder(services);
+            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
+            {
+                h.Name = name;
+                h.Number = number;
+                h.ViewDataValue = vc.ViewData["TestData"];
+            });
+            var httpContext = MakeHttpContext(services.BuildServiceProvider());
+            var viewContext = MakeViewContext(httpContext);
+            var viewDataValue = new object();
+            viewContext.ViewData.Add("TestData", viewDataValue);
+            var factory = CreateFactory();
+
+            // Act
+            var helper = factory.CreateTagHelper<TestTagHelper>(viewContext);
+
+            // Assert
+            Assert.Equal(name, helper.Name);
+            Assert.Equal(number, helper.Number);
+            Assert.Same(viewDataValue, helper.ViewDataValue);
+        }
+
+        [Fact]
+        public void CreateTagHelper_InitializesTagHelpersAfterActivatingProperties()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            var builder = new MvcCoreBuilder(services);
+            builder.InitializeTagHelper<TestTagHelper>((h, _) => h.ViewContext = MakeViewContext(MakeHttpContext()));
+            var httpContext = MakeHttpContext(services.BuildServiceProvider());
+            var viewContext = MakeViewContext(httpContext);
+            var factory = CreateFactory();
+
+            // Act
+            var helper = factory.CreateTagHelper<TestTagHelper>(viewContext);
+
+            // Assert
+            Assert.NotSame(viewContext, helper.ViewContext);
+        }
+
+        [Fact]
+        public void CreateTagHelper_InitializesTagHelpersWithMultipleInitializers()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            var builder = new MvcCoreBuilder(services);
+            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
+            {
+                h.Name = "Test 1";
+                h.Number = 100;
+            });
+            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
+            {
+                h.Name += ", Test 2";
+                h.Number += 100;
+            });
+            var httpContext = MakeHttpContext(services.BuildServiceProvider());
+            var viewContext = MakeViewContext(httpContext);
+            var factory = CreateFactory();
+
+            // Act
+            var helper = factory.CreateTagHelper<TestTagHelper>(viewContext);
+
+            // Assert
+            Assert.Equal("Test 1, Test 2", helper.Name);
+            Assert.Equal(200, helper.Number);
+        }
+
+        [Fact]
+        public void CreateTagHelper_InitializesTagHelpersWithCorrectInitializers()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            var builder = new MvcCoreBuilder(services);
+            builder.InitializeTagHelper<TestTagHelper>((h, vc) =>
+            {
+                h.Name = "Test 1";
+                h.Number = 100;
+            });
+            builder.InitializeTagHelper<AnotherTestTagHelper>((h, vc) =>
+            {
+                h.Name = "Test 2";
+                h.Number = 102;
+            });
+            var httpContext = MakeHttpContext(services.BuildServiceProvider());
+            var viewContext = MakeViewContext(httpContext);
+
+            var activator = new Mock<ITagHelperActivator>();
+            activator
+                .Setup(a => a.Create<TestTagHelper>(It.IsAny<ViewContext>()))
+                .Returns(new TestTagHelper());
+
+            activator
+                .Setup(a => a.Create<AnotherTestTagHelper>(It.IsAny<ViewContext>()))
+                .Returns(new AnotherTestTagHelper());
+
+            var factory = new DefaultTagHelperFactory(activator.Object);
+
+            // Act
+            var testTagHelper = factory.CreateTagHelper<TestTagHelper>(viewContext);
+            var anotherTestTagHelper = factory.CreateTagHelper<AnotherTestTagHelper>(viewContext);
+
+            // Assert
+            Assert.Equal("Test 1", testTagHelper.Name);
+            Assert.Equal(100, testTagHelper.Number);
+            Assert.Equal("Test 2", anotherTestTagHelper.Name);
+            Assert.Equal(102, anotherTestTagHelper.Number);
+        }
+
+        private static HttpContext MakeHttpContext(IServiceProvider services = null)
+        {
+            var httpContext = new DefaultHttpContext();
+            if (services != null)
+            {
+                httpContext.RequestServices = services;
+            }
+            return httpContext;
+        }
+
+        private static DefaultTagHelperFactory CreateFactory()
+        {
+            var activator = new Mock<ITagHelperActivator>();
+            activator.Setup(a => a.Create<TestTagHelper>(It.IsAny<ViewContext>())).Returns(new TestTagHelper());
+            return new DefaultTagHelperFactory(activator.Object);
+        }
+
+        private static ViewContext MakeViewContext(HttpContext httpContext)
+        {
+            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
+            var metadataProvider = new EmptyModelMetadataProvider();
+            var viewData = new ViewDataDictionary(metadataProvider);
+            var viewContext = new ViewContext(
+                actionContext,
+                Mock.Of<IView>(),
+                viewData,
+                Mock.Of<ITempDataDictionary>(),
+                TextWriter.Null,
+                new HtmlHelperOptions());
+
+            return viewContext;
+        }
+
+        private class TestTagHelper : TagHelper
+        {
+            public string Name { get; set; } = "Initial Name";
+
+            public int Number { get; set; } = 1000;
+
+            public object ViewDataValue { get; set; } = new object();
+
+            [ViewContext]
+            public ViewContext ViewContext { get; set; }
+        }
+
+        private class AnotherTestTagHelper : TagHelper
+        {
+            public string Name { get; set; } = "Initial Name";
+
+            public int Number { get; set; } = 1000;
+
+            public object ViewDataValue { get; set; } = new object();
+
+            [ViewContext]
+            public ViewContext ViewContext { get; set; }
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorPageCreateTagHelperTest.cs

@@ -69,11 +69,14 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             var activator = new RazorPageActivator(new EmptyModelMetadataProvider());
             var serviceProvider = new Mock<IServiceProvider>();
             var typeActivator = new TypeActivatorCache();
+            var tagHelperActivator = new DefaultTagHelperActivator(typeActivator);
             var myService = new MyService();
             serviceProvider.Setup(mock => mock.GetService(typeof(MyService)))
                            .Returns(myService);
+            serviceProvider.Setup(mock => mock.GetService(typeof(ITagHelperFactory)))
+                .Returns(new DefaultTagHelperFactory(tagHelperActivator));
             serviceProvider.Setup(mock => mock.GetService(typeof(ITagHelperActivator)))
-                           .Returns(new DefaultTagHelperActivator());
+                           .Returns(tagHelperActivator);
             serviceProvider.Setup(mock => mock.GetService(typeof(ITypeActivatorCache)))
                            .Returns(typeActivator);
             serviceProvider.Setup(mock => mock.GetService(It.Is<Type>(serviceType =>