Make ComponentFactory do all the reflection up-front and cache the resulting delegates

src/Microsoft.AspNetCore.Blazor/Components/ComponentFactory.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Reflection;
 
 namespace Microsoft.AspNetCore.Blazor.Components
@@ -11,6 +13,8 @@ namespace Microsoft.AspNetCore.Blazor.Components
         private readonly IServiceProvider _serviceProvider;
         private readonly static BindingFlags _injectablePropertyBindingFlags
             = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
+        private readonly IDictionary<Type, Action<IComponent>> _cachedInitializers
+            = new Dictionary<Type, Action<IComponent>>();
 
         public ComponentFactory(IServiceProvider serviceProvider)
         {
@@ -33,25 +37,68 @@ namespace Microsoft.AspNetCore.Blazor.Components
 
         private void PerformPropertyInjection(IComponent instance)
         {
-            // TODO: Cache delegates, etc
-            var type = instance.GetType();
-            var properties = type.GetTypeInfo().GetProperties(_injectablePropertyBindingFlags);
-            foreach (var property in properties)
+            var instanceType = instance.GetType();
+            if (!_cachedInitializers.TryGetValue(instanceType, out var initializer))
             {
-                var injectAttribute = property.GetCustomAttribute<InjectAttribute>();
-                if (injectAttribute != null)
+                initializer = CreateInitializer(instanceType);
+                _cachedInitializers[instanceType] = initializer;
+            }
+
+            initializer(instance);
+        }
+
+        private Action<IComponent> CreateInitializer(Type type)
+        {
+            // Do all the reflection up front
+            var injectableProperties = type.GetTypeInfo()
+                .GetProperties(_injectablePropertyBindingFlags)
+                .Where(p => p.GetCustomAttribute<InjectAttribute>() != null)
+                .Where(p => p.SetMethod != null);
+            var injectables = injectableProperties.Select(property =>
+            (
+                propertyName: property.Name,
+                propertyType: property.PropertyType,
+                setter: (IPropertySetter)Activator.CreateInstance(
+                    typeof(PropertySetter<,>).MakeGenericType(type, property.PropertyType),
+                    property.SetMethod)
+            )).ToArray();
+
+            // Return an action whose closure can write all the injected properties
+            // without any further reflection calls (just typecasts)
+            return instance =>
+            {
+                foreach (var injectable in injectables)
                 {
-                    var serviceInstance = _serviceProvider.GetService(property.PropertyType);
+                    var serviceInstance = _serviceProvider.GetService(injectable.propertyType);
                     if (serviceInstance == null)
                     {
                         throw new InvalidOperationException($"Cannot provide value for property " +
-                            $"'{property.Name}' on type '{type.FullName}'. There is no registered " +
-                            $"service of type '{property.PropertyType.FullName}'.");
+                            $"'{injectable.propertyName}' on type '{type.FullName}'. There is no " +
+                            $"registered service of type '{injectable.propertyType}'.");
                     }
 
-                    property.SetValue(instance, serviceInstance);
+                    injectable.setter.SetValue(instance, serviceInstance);
                 }
+            };
+        }
+
+        private interface IPropertySetter
+        {
+            void SetValue(object target, object value);
+        }
+
+        private class PropertySetter<TTarget, TValue> : IPropertySetter
+        {
+            private readonly Action<TTarget, TValue> _setterDelegate;
+
+            public PropertySetter(MethodInfo setMethod)
+            {
+                _setterDelegate = (Action<TTarget, TValue>)Delegate.CreateDelegate(
+                    typeof(Action<TTarget, TValue>), setMethod);
             }
+
+            public void SetValue(object target, object value)
+                => _setterDelegate((TTarget)target, (TValue)value);
         }
     }
 }

test/Microsoft.AspNetCore.Blazor.Test/DependencyInjectionTest.cs

@@ -41,6 +41,16 @@ namespace Microsoft.AspNetCore.Blazor.Test
             Assert.Null(HasStaticProperties.StaticPropertyWithoutInject);
         }
 
+        [Fact]
+        public void IgnoresGetOnlyProperties()
+        {
+            // Arrange/Act
+            var component = InstantiateComponent<HasGetOnlyProperty>();
+
+            // Assert
+            Assert.Null(component.MyService);
+        }
+
         [Fact]
         public void ThrowsIfNoSuchServiceIsRegistered()
         {
@@ -119,7 +129,12 @@ namespace Microsoft.AspNetCore.Blazor.Test
             [Inject] public static IMyService StaticPropertyWithInject { get; set; }
             public static IMyService StaticPropertyWithoutInject { get; set; }
         }
-        
+
+        class HasGetOnlyProperty : TestComponent
+        {
+            [Inject] public IMyService MyService { get; }
+        }
+
         class HasInjectableProperty : TestComponent
         {
             [Inject] public IMyService MyService { get; set; }