- allow async onCreate method by introducing async resolve

LightweightIocContainer.sln.DotSettings

@@ -4,16 +4,21 @@
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 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/USE_INDENT_FROM_VS/@EntryValue">False</s:Boolean>
 	<s:Int64 x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_LIMIT/@EntryValue">200</s:Int64>
-	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue">Author: $USER_NAME$&#xD;
+	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue">Author: ${User.Name}&#xD;
-Created: $CREATED_YEAR$-$CREATED_MONTH$-$CREATED_DAY$&#xD;
+Created: ${File.CreatedYear}-${File.CreatedMonth}-${File.CreatedDay}&#xD;
-Copyright(c) $CREATED_YEAR$ SimonG. All Rights Reserved.</s:String>
+Copyright(c) ${File.CreatedYear} SimonG. All Rights Reserved.</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/PredefinedNamingRules/=Method/@EntryIndexedValue">&lt;Policy Inspect="True" Prefix="" Suffix="" Style="AaBb" /&gt;</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/PredefinedNamingRules/=PrivateConstants/@EntryIndexedValue">&lt;Policy Inspect="True" Prefix="" Suffix="" Style="AA_BB" /&gt;</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/PredefinedNamingRules/=PrivateStaticReadonly/@EntryIndexedValue">&lt;Policy Inspect="True" Prefix="_" Suffix="" Style="aaBb" /&gt;</s:String>
+	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/UserRules/=15b5b1f1_002D457c_002D4ca6_002Db278_002D5615aedc07d3/@EntryIndexedValue">&lt;Policy&gt;&lt;Descriptor Staticness="Static" AccessRightKinds="Private" Description="Static readonly fields (private)"&gt;&lt;ElementKinds&gt;&lt;Kind Name="READONLY_FIELD" /&gt;&lt;/ElementKinds&gt;&lt;/Descriptor&gt;&lt;Policy Inspect="True" WarnAboutPrefixesAndSuffixes="False" Prefix="_" Suffix="" Style="aaBb" /&gt;&lt;/Policy&gt;</s:String>
+	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/UserRules/=236f7aa5_002D7b06_002D43ca_002Dbf2a_002D9b31bfcff09a/@EntryIndexedValue">&lt;Policy&gt;&lt;Descriptor Staticness="Any" AccessRightKinds="Private" Description="Constant fields (private)"&gt;&lt;ElementKinds&gt;&lt;Kind Name="CONSTANT_FIELD" /&gt;&lt;/ElementKinds&gt;&lt;/Descriptor&gt;&lt;Policy Inspect="True" WarnAboutPrefixesAndSuffixes="False" Prefix="" Suffix="" Style="AA_BB" /&gt;&lt;/Policy&gt;</s:String>
+	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/UserRules/=8284009d_002De743_002D4d89_002D9402_002Da5bf9a89b657/@EntryIndexedValue">&lt;Policy&gt;&lt;Descriptor Staticness="Any" AccessRightKinds="Any" Description="Methods"&gt;&lt;ElementKinds&gt;&lt;Kind Name="METHOD" /&gt;&lt;/ElementKinds&gt;&lt;/Descriptor&gt;&lt;Policy Inspect="True" WarnAboutPrefixesAndSuffixes="False" Prefix="" Suffix="" Style="AaBb" /&gt;&lt;/Policy&gt;</s:String>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EFeature_002EServices_002ECodeCleanup_002EFileHeader_002EFileHeaderSettingsMigrate/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpKeepExistingMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpPlaceEmbeddedOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpUseContinuousIndentInsideBracesMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateBlankLinesAroundFieldToBlankLinesAroundProperty/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EPredefinedNamingRulesToUserRulesUpgrade/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=gockner/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=multiton/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=multitons/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>

LightweightIocContainer/Factories/TypedFactory.cs

@@ -51,7 +51,7 @@ public class TypedFactory<TFactory> : TypedFactoryBase<TFactory>, ITypedFactory<
         FieldBuilder helperFieldBuilder = typeBuilder.DefineField("_helper", typeof(FactoryHelper), FieldAttributes.Private | FieldAttributes.InitOnly);
 
         //add ctor
-        ConstructorBuilder constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, new[] {typeof(IocContainer), typeof(FactoryHelper)});
+        ConstructorBuilder constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, [typeof(IocContainer), typeof(FactoryHelper)]);
         ILGenerator constructorGenerator = constructorBuilder.GetILGenerator();
         constructorGenerator.Emit(OpCodes.Ldarg_0);
         constructorGenerator.Emit(OpCodes.Ldarg_1);
@@ -129,13 +129,18 @@ public class TypedFactory<TFactory> : TypedFactoryBase<TFactory>, ITypedFactory<
                 generator.EmitCall(OpCodes.Call, emptyArray, null);
             }
             
-            generator.EmitCall(OpCodes.Call, typeof(FactoryHelper).GetMethod(nameof(FactoryHelper.ConvertPassedNull), new[] { typeof(MethodBase), typeof(object?[]) })!, null);
+            generator.EmitCall(OpCodes.Call, typeof(FactoryHelper).GetMethod(nameof(FactoryHelper.ConvertPassedNull), [typeof(MethodBase), typeof(object?[])])!, null);
             generator.Emit(OpCodes.Stloc_1);
             generator.Emit(OpCodes.Ldarg_0);
             generator.Emit(OpCodes.Ldfld, containerFieldBuilder);
             generator.Emit(OpCodes.Ldloc_1);
 
-            generator.EmitCall(OpCodes.Call, typeof(IocContainer).GetMethod(nameof(IocContainer.FactoryResolve), new[] { typeof(object?[]) })!.MakeGenericMethod(createMethod.ReturnType), null);
+            Type? asyncReturnType = createMethod.ReturnType.GetAsyncReturnType();
+            if (asyncReturnType is not null)
+                generator.EmitCall(OpCodes.Call, typeof(IocContainer).GetMethod(nameof(IocContainer.FactoryResolveAsync), [typeof(object?[])])!.MakeGenericMethod(asyncReturnType), null);
+            else
+                generator.EmitCall(OpCodes.Call, typeof(IocContainer).GetMethod(nameof(IocContainer.FactoryResolve), [typeof(object?[])])!.MakeGenericMethod(createMethod.ReturnType), null);
+            
             generator.Emit(OpCodes.Castclass, createMethod.ReturnType);
             generator.Emit(OpCodes.Ret);
         }

LightweightIocContainer/GenericMethodCaller.cs

@@ -41,6 +41,31 @@ internal static class GenericMethodCaller
         }
     }
     
+    public static async Task<object?> CallAsync(object caller, string functionName, Type genericParameter, BindingFlags bindingFlags, params object?[] parameters)
+    {
+        MethodInfo? method = caller.GetType().GetMethod(functionName, bindingFlags);
+        MethodInfo? genericMethod = method?.MakeGenericMethod(genericParameter);
+
+        if (genericMethod == null)
+            throw new GenericMethodNotFoundException(functionName);
+
+        try //exceptions thrown by methods called with invoke are wrapped into another exception, the exception thrown by the invoked method can be returned by `Exception.GetBaseException()`
+        {
+            object? result = genericMethod.Invoke(caller, parameters);
+            if (result is null)
+                return null;
+            
+            if (result is Task<object?> task)
+                return await task;
+
+            return result;
+        }
+        catch (Exception ex)
+        {
+            throw ex.GetBaseException();
+        }
+    }
+
     /// <summary>
     /// Call a private generic method without generic type parameters
     /// </summary>
@@ -53,4 +78,7 @@ internal static class GenericMethodCaller
     /// <exception cref="Exception">Any <see cref="Exception"/> thrown after invoking the generic method</exception>
     public static object? CallPrivate(object caller, string functionName, Type genericParameter, params object?[] parameters) =>
         Call(caller, functionName, genericParameter, BindingFlags.NonPublic | BindingFlags.Instance, parameters);
+    
+    public static async Task<object?> CallPrivateAsync(object caller, string functionName, Type genericParameter, params object?[] parameters) =>
+        await CallAsync(caller, functionName, genericParameter, BindingFlags.NonPublic | BindingFlags.Instance, parameters);
 }

LightweightIocContainer/Interfaces/IIocResolver.cs

@@ -16,6 +16,13 @@ public interface IIocResolver : IDisposable
     /// <returns>An instance of the given <see cref="Type"/></returns>
     T Resolve<T>();
     
+    /// <summary>
+    /// Gets an instance of the given <see cref="Type"/>
+    /// </summary>
+    /// <typeparam name="T">The given <see cref="Type"/></typeparam>
+    /// <returns>An instance of the given <see cref="Type"/></returns>
+    Task<T> ResolveAsync<T>();
+
     /// <summary>
     /// Gets an instance of the given <see cref="Type"/>
     /// </summary>
@@ -23,4 +30,12 @@ public interface IIocResolver : IDisposable
     /// <param name="arguments">The constructor arguments</param>
     /// <returns>An instance of the given <see cref="Type"/></returns>
     T Resolve<T>(params object[] arguments);
+    
+    /// <summary>
+    /// Gets an instance of the given <see cref="Type"/>
+    /// </summary>
+    /// <typeparam name="T">The given <see cref="Type"/></typeparam>
+    /// <param name="arguments">The constructor arguments</param>
+    /// <returns>An instance of the given <see cref="Type"/></returns>
+    Task<T> ResolveAsync<T>(params object[] arguments);
 }

LightweightIocContainer/Interfaces/Registrations/Fluent/IOnCreate.cs

@@ -16,6 +16,7 @@ public interface IOnCreate
     /// <para>Can be set in the <see cref="IIocInstaller"/> by calling <see cref="IOnCreate{TInterface, TImplementation}.OnCreate"/></para>
     /// </summary>
     internal Action<object?>? OnCreateAction { get; }
+    internal Func<object?, Task>? OnCreateActionAsync { get; }
 }
 
 /// <summary>
@@ -31,4 +32,6 @@ public interface IOnCreate<TInterface, TImplementation> : IOnCreate where TImple
     /// <param name="action">The <see cref="Action{T}"/></param>
     /// <returns>The current instance of this <see cref="ITypedRegistration{TInterface,TImplementation}"/></returns>
     ITypedRegistration<TInterface, TImplementation> OnCreate(Action<TImplementation?> action);
+    
+    ITypedRegistration<TInterface, TImplementation> OnCreateAsync(Func<TImplementation?, Task> action);
 }

LightweightIocContainer/IocContainer.cs

@@ -104,6 +104,13 @@ public class IocContainer : IIocContainer, IIocResolver
     /// <returns>An instance of the given <see cref="Type"/></returns>
     public virtual T Resolve<T>() => ResolveInternal<T>(null);
 
+    /// <summary>
+    /// Gets an instance of the given <see cref="Type"/>
+    /// </summary>
+    /// <typeparam name="T">The given <see cref="Type"/></typeparam>
+    /// <returns>An instance of the given <see cref="Type"/></returns>
+    public Task<T> ResolveAsync<T>() => ResolveInternalAsync<T>(null);
+
     /// <summary>
     /// Gets an instance of the given <see cref="Type"/>
     /// </summary>
@@ -112,6 +119,14 @@ public class IocContainer : IIocContainer, IIocResolver
     /// <returns>An instance of the given <see cref="Type"/></returns>
     public T Resolve<T>(params object[] arguments) => ResolveInternal<T>(arguments);
 
+    /// <summary>
+    /// Gets an instance of the given <see cref="Type"/>
+    /// </summary>
+    /// <typeparam name="T">The given <see cref="Type"/></typeparam>
+    /// <param name="arguments">The constructor arguments</param>
+    /// <returns>An instance of the given <see cref="Type"/></returns>
+    public Task<T> ResolveAsync<T>(params object[] arguments) => ResolveInstanceAsync<T>(arguments);
+
     /// <summary>
     /// Gets an instance of the given <see cref="Type"/> for a factory
     /// </summary>
@@ -120,6 +135,14 @@ public class IocContainer : IIocContainer, IIocResolver
     /// <returns>An instance of the given <see cref="Type"/></returns>
     public T FactoryResolve<T>(params object?[] arguments) => ResolveInternal<T>(arguments, null, true);
     
+    /// <summary>
+    /// Gets an instance of the given <see cref="Type"/> for a factory
+    /// </summary>
+    /// <typeparam name="T">The given <see cref="Type"/></typeparam>
+    /// <param name="arguments">The constructor arguments</param>
+    /// <returns>An instance of the given <see cref="Type"/></returns>
+    public Task<T> FactoryResolveAsync<T>(params object?[] arguments) => ResolveInternalAsync<T>(arguments, null, true);
+
     /// <summary>
     /// Gets an instance of a given registered <see cref="Type"/>
     /// </summary>
@@ -140,6 +163,18 @@ public class IocContainer : IIocContainer, IIocResolver
         throw new Exception("Resolve Error");
     }
     
+    private async Task<T> ResolveInternalAsync<T>(object?[]? arguments, List<Type>? resolveStack = null, bool isFactoryResolve = false)
+    {
+        (bool success, object resolvedObject, Exception? exception) = TryResolve<T>(arguments, resolveStack, isFactoryResolve);
+        if (success)
+            return await ResolveInstanceAsync<T>(resolvedObject);
+
+        if (exception is not null)
+            throw exception;
+
+        throw new Exception("Resolve Error");
+    }
+
     /// <summary>
     /// Tries to resolve the given <see cref="Type"/> with the given arguments
     /// </summary>
@@ -254,7 +289,7 @@ public class IocContainer : IIocContainer, IIocResolver
         if (toBeResolvedPlaceholder.Parameters == null)
             return CreateInstance<T>(toBeResolvedPlaceholder.ResolvedRegistration, null);
             
-        List<object?> parameters = new();
+        List<object?> parameters = [];
         foreach (object? parameter in toBeResolvedPlaceholder.Parameters)
         {
             if (parameter != null)
@@ -271,6 +306,32 @@ public class IocContainer : IIocContainer, IIocResolver
         return CreateInstance<T>(toBeResolvedPlaceholder.ResolvedRegistration, parameters.ToArray());
     }
 
+    private async Task<T> ResolvePlaceholderAsync<T>(InternalToBeResolvedPlaceholder toBeResolvedPlaceholder)
+    {
+        object? existingInstance = TryGetExistingInstance<T>(toBeResolvedPlaceholder.ResolvedRegistration, toBeResolvedPlaceholder.Parameters);
+        if (existingInstance is T instance)
+            return instance;
+
+        if (toBeResolvedPlaceholder.Parameters == null)
+            return await CreateInstanceAsync<T>(toBeResolvedPlaceholder.ResolvedRegistration, null);
+            
+        List<object?> parameters = [];
+        foreach (object? parameter in toBeResolvedPlaceholder.Parameters)
+        {
+            if (parameter != null)
+            {
+                Type type = parameter is IInternalToBeResolvedPlaceholder internalToBeResolvedPlaceholder ?
+                    internalToBeResolvedPlaceholder.ResolvedType : parameter.GetType();
+                    
+                parameters.Add(await ResolveInstanceNonGenericAsync(type, parameter));
+            }
+            else
+                parameters.Add(parameter);
+        }
+
+        return await CreateInstanceAsync<T>(toBeResolvedPlaceholder.ResolvedRegistration, parameters.ToArray());
+    }
+
     /// <summary>
     /// Resolve the given object instance
     /// </summary>
@@ -287,6 +348,15 @@ public class IocContainer : IIocContainer, IIocResolver
             _ => throw new InternalResolveException("Resolve returned wrong type.")
         };
     
+    private async Task<T> ResolveInstanceAsync<T>(object resolvedObject) =>
+        resolvedObject switch
+        {
+            T instance => instance,
+            InternalToBeResolvedPlaceholder toBeResolvedPlaceholder => await ResolvePlaceholderAsync<T>(toBeResolvedPlaceholder),
+            InternalFactoryMethodPlaceholder<T> factoryMethodPlaceholder => await CreateInstanceAsync<T>(factoryMethodPlaceholder.SingleTypeRegistration, null),
+            _ => throw new InternalResolveException("Resolve returned wrong type.")
+        };
+
     /// <summary>
     /// Resolve the given object instance without generic arguments
     /// </summary>
@@ -297,6 +367,9 @@ public class IocContainer : IIocContainer, IIocResolver
     private object? ResolveInstanceNonGeneric(Type type, object resolvedObject) => 
         GenericMethodCaller.CallPrivate(this, nameof(ResolveInstance), type, resolvedObject);
     
+    private Task<object?> ResolveInstanceNonGenericAsync(Type type, object resolvedObject) => 
+        GenericMethodCaller.CallPrivateAsync(this, nameof(ResolveInstance), type, resolvedObject);
+
     /// <summary>
     /// Creates an instance of a given <see cref="Type"/>
     /// </summary>
@@ -326,7 +399,16 @@ public class IocContainer : IIocContainer, IIocResolver
             _singletons.Add((GetType<T>(registration), instance));
 
         if (registration is IOnCreate onCreateRegistration)
-            onCreateRegistration.OnCreateAction?.Invoke(instance); //TODO: Allow async OnCreateAction?
+            onCreateRegistration.OnCreateAction?.Invoke(instance);
+
+        return instance;
+    }
+
+    private async Task<T> CreateInstanceAsync<T>(IRegistration registration, object?[]? arguments)
+    {
+        T instance = CreateInstance<T>(registration, arguments);
+        if (registration is IOnCreate { OnCreateActionAsync: not null } onCreateRegistration)
+            await onCreateRegistration.OnCreateActionAsync.Invoke(instance);
 
         return instance;
     }

LightweightIocContainer/LightweightIocContainer.xml

@@ -551,6 +551,13 @@
             <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
             <returns>An instance of the given <see cref="T:System.Type"/></returns>
         </member>
+        <member name="M:LightweightIocContainer.Interfaces.IIocResolver.ResolveAsync``1">
+            <summary>
+            Gets an instance of the given <see cref="T:System.Type"/>
+            </summary>
+            <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
+            <returns>An instance of the given <see cref="T:System.Type"/></returns>
+        </member>
         <member name="M:LightweightIocContainer.Interfaces.IIocResolver.Resolve``1(System.Object[])">
             <summary>
             Gets an instance of the given <see cref="T:System.Type"/>
@@ -559,6 +566,14 @@
             <param name="arguments">The constructor arguments</param>
             <returns>An instance of the given <see cref="T:System.Type"/></returns>
         </member>
+        <member name="M:LightweightIocContainer.Interfaces.IIocResolver.ResolveAsync``1(System.Object[])">
+            <summary>
+            Gets an instance of the given <see cref="T:System.Type"/>
+            </summary>
+            <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
+            <param name="arguments">The constructor arguments</param>
+            <returns>An instance of the given <see cref="T:System.Type"/></returns>
+        </member>
         <member name="T:LightweightIocContainer.Interfaces.Installers.IAssemblyInstaller">
             <summary>
             An <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/> that installs all <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/>s for its given <see cref="T:System.Reflection.Assembly"/>
@@ -975,6 +990,13 @@
             <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
             <returns>An instance of the given <see cref="T:System.Type"/></returns>
         </member>
+        <member name="M:LightweightIocContainer.IocContainer.ResolveAsync``1">
+            <summary>
+            Gets an instance of the given <see cref="T:System.Type"/>
+            </summary>
+            <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
+            <returns>An instance of the given <see cref="T:System.Type"/></returns>
+        </member>
         <member name="M:LightweightIocContainer.IocContainer.Resolve``1(System.Object[])">
             <summary>
             Gets an instance of the given <see cref="T:System.Type"/>
@@ -983,6 +1005,14 @@
             <param name="arguments">The constructor arguments</param>
             <returns>An instance of the given <see cref="T:System.Type"/></returns>
         </member>
+        <member name="M:LightweightIocContainer.IocContainer.ResolveAsync``1(System.Object[])">
+            <summary>
+            Gets an instance of the given <see cref="T:System.Type"/>
+            </summary>
+            <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
+            <param name="arguments">The constructor arguments</param>
+            <returns>An instance of the given <see cref="T:System.Type"/></returns>
+        </member>
         <member name="M:LightweightIocContainer.IocContainer.FactoryResolve``1(System.Object[])">
             <summary>
             Gets an instance of the given <see cref="T:System.Type"/> for a factory
@@ -991,6 +1021,14 @@
             <param name="arguments">The constructor arguments</param>
             <returns>An instance of the given <see cref="T:System.Type"/></returns>
         </member>
+        <member name="M:LightweightIocContainer.IocContainer.FactoryResolveAsync``1(System.Object[])">
+            <summary>
+            Gets an instance of the given <see cref="T:System.Type"/> for a factory
+            </summary>
+            <typeparam name="T">The given <see cref="T:System.Type"/></typeparam>
+            <param name="arguments">The constructor arguments</param>
+            <returns>An instance of the given <see cref="T:System.Type"/></returns>
+        </member>
         <member name="M:LightweightIocContainer.IocContainer.ResolveInternal``1(System.Object[],System.Collections.Generic.List{System.Type},System.Boolean)">
             <summary>
             Gets an instance of a given registered <see cref="T:System.Type"/>
@@ -1856,12 +1894,24 @@
             <para>Can be set in the <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/> by calling <see cref="M:LightweightIocContainer.Interfaces.Registrations.Fluent.IOnCreate`2.OnCreate(System.Action{`1})"/></para>
             </summary>
         </member>
+        <member name="P:LightweightIocContainer.Registrations.TypedRegistration`2.OnCreateActionAsync">
+            <summary>
+            This <see cref="T:System.Action"/> is invoked when an instance of this type is created.
+            <para>Can be set in the <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/> by calling <see cref="M:LightweightIocContainer.Interfaces.Registrations.Fluent.IOnCreate`2.OnCreate(System.Action{`1})"/></para>
+            </summary>
+        </member>
         <member name="P:LightweightIocContainer.Registrations.TypedRegistration`2.LightweightIocContainer#Interfaces#Registrations#Fluent#IOnCreate#OnCreateAction">
             <summary>
             This <see cref="T:System.Action"/> is invoked when an instance of this type is created.
             <para>Can be set in the <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/> by calling <see cref="M:LightweightIocContainer.Interfaces.Registrations.Fluent.IOnCreate`2.OnCreate(System.Action{`1})"/></para>
             </summary>
         </member>
+        <member name="P:LightweightIocContainer.Registrations.TypedRegistration`2.LightweightIocContainer#Interfaces#Registrations#Fluent#IOnCreate#OnCreateActionAsync">
+            <summary>
+            This <see cref="T:System.Action"/> is invoked when an instance of this type is created.
+            <para>Can be set in the <see cref="T:LightweightIocContainer.Interfaces.Installers.IIocInstaller"/> by calling <see cref="M:LightweightIocContainer.Interfaces.Registrations.Fluent.IOnCreate`2.OnCreate(System.Action{`1})"/></para>
+            </summary>
+        </member>
         <member name="M:LightweightIocContainer.Registrations.TypedRegistration`2.OnCreate(System.Action{`1})">
             <summary>
             Pass an <see cref="T:System.Action`1"/> that will be invoked when an instance of this type is created

LightweightIocContainer/Registrations/RegistrationBase.cs

@@ -176,7 +176,7 @@ internal abstract class RegistrationBase : IRegistrationBase, IWithFactoryIntern
         if (Factory == null)
             return;
             
-        if (Factory.CreateMethods.All(c => c.ReturnType != InterfaceType))
+        if (Factory.CreateMethods.All(c => c.ReturnType != InterfaceType) && Factory.CreateMethods.All(c => c.ReturnType.GetAsyncReturnType() != InterfaceType))
             throw new InvalidFactoryRegistrationException($"No create method that can create {InterfaceType}.");
     }
         

LightweightIocContainer/Registrations/TypedRegistration.cs

@@ -36,12 +36,24 @@ internal class TypedRegistration<TInterface, TImplementation> : RegistrationBase
     /// </summary>
     private Action<object?>? OnCreateAction { get; set; }
 
+    /// <summary>
+    /// This <see cref="Action"/> is invoked when an instance of this type is created.
+    /// <para>Can be set in the <see cref="IIocInstaller"/> by calling <see cref="IOnCreate{TInterface,TImplementation}.OnCreate"/></para>
+    /// </summary>
+    private Func<object?, Task>? OnCreateActionAsync { get; set; }
+
     /// <summary>
     /// This <see cref="Action"/> is invoked when an instance of this type is created.
     /// <para>Can be set in the <see cref="IIocInstaller"/> by calling <see cref="IOnCreate{TInterface,TImplementation}.OnCreate"/></para>
     /// </summary>
     Action<object?>? IOnCreate.OnCreateAction => OnCreateAction;
     
+    /// <summary>
+    /// This <see cref="Action"/> is invoked when an instance of this type is created.
+    /// <para>Can be set in the <see cref="IIocInstaller"/> by calling <see cref="IOnCreate{TInterface,TImplementation}.OnCreate"/></para>
+    /// </summary>
+    Func<object?, Task>? IOnCreate.OnCreateActionAsync => OnCreateActionAsync;
+
     /// <summary>
     /// Pass an <see cref="Action{T}"/> that will be invoked when an instance of this type is created
     /// </summary>
@@ -53,6 +65,12 @@ internal class TypedRegistration<TInterface, TImplementation> : RegistrationBase
         return this;
     }
 
+    public ITypedRegistration<TInterface, TImplementation> OnCreateAsync(Func<TImplementation?, Task> action)
+    {
+        OnCreateActionAsync = a => action((TImplementation?) a);
+        return this;
+    }
+
     /// <summary>
     /// Validate the <see cref="DisposeStrategy"/> for the <see cref="ImplementationType"/> and <see cref="Lifestyle"/>
     /// </summary>
@@ -72,6 +90,12 @@ internal class TypedRegistration<TInterface, TImplementation> : RegistrationBase
         if (OnCreateAction != null && typedRegistration.OnCreateAction == null)
             return false;
         
+        if (OnCreateActionAsync == null && typedRegistration.OnCreateActionAsync != null)
+            return false;
+
+        if (OnCreateActionAsync != null && typedRegistration.OnCreateActionAsync == null)
+            return false;
+            
         return ImplementationType == typedRegistration.ImplementationType;
     }
 

LightweightIocContainer/TypeExtension.cs

@@ -12,4 +12,14 @@ internal static class TypeExtension
     /// <param name="type">The given <see cref="Type"/></param>
     /// <returns>The default value for the given <see cref="Type"/></returns>
     public static object? GetDefault(this Type type) => type.IsValueType ? Activator.CreateInstance(type) : null;
+    public static Type? GetAsyncReturnType(this Type type)
+    {
+        if (!type.IsGenericType)
+            return null;
+        
+        if (type.GetGenericTypeDefinition() != typeof(Task<>))
+            return null;
+        
+        return type.GenericTypeArguments[0];
+    }
 }

Test.LightweightIocContainer/AsyncFactoryTest.cs

@@ -0,0 +1,96 @@
+// Author: simon.gockner
+// Created: 2024-11-25
+// Copyright(c) 2024 SimonG. All Rights Reserved.
+
+using LightweightIocContainer;
+using NUnit.Framework;
+
+namespace Test.LightweightIocContainer;
+
+[TestFixture]
+public class AsyncFactoryTest
+{
+    public interface ITest
+    {
+        bool IsInitialized { get; }
+        Task Initialize();
+    }
+    
+    public class Test : ITest
+    {
+        public bool IsInitialized { get; private set; }
+
+        public virtual async Task Initialize()
+        {
+            await Task.Delay(200);
+            IsInitialized = true;
+        }
+    }
+
+    public class MultitonTest(int id) : Test
+    {
+        public int Id { get; } = id;
+        public override async Task Initialize()
+        {
+            if (IsInitialized)
+                throw new Exception();
+            
+            await base.Initialize();
+        }
+    }
+    
+    public interface ITestFactory
+    {
+        Task<ITest> Create();
+    }
+    
+    public interface IMultitonTestFactory
+    {
+        Task<ITest> Create(int id);
+    }
+    
+    [Test]
+    public async Task TestAsyncFactoryResolve()
+    {
+        IocContainer container = new();
+        container.Register(r => r.Add<ITest, Test>().WithFactory<ITestFactory>());
+
+        ITestFactory testFactory = container.Resolve<ITestFactory>();
+        ITest test = await testFactory.Create();
+        
+        Assert.IsInstanceOf<Test>(test);
+    }
+    
+    [Test]
+    public async Task TestAsyncFactoryResolveOnCreateCalled()
+    {
+        IocContainer container = new();
+        container.Register(r => r.Add<ITest, Test>().OnCreateAsync(t => t.Initialize()).WithFactory<ITestFactory>());
+
+        ITestFactory testFactory = container.Resolve<ITestFactory>();
+        ITest test = await testFactory.Create();
+        
+        Assert.IsInstanceOf<Test>(test);
+        Assert.That(test.IsInitialized, Is.True);
+    }
+
+    [Test]
+    public async Task TestAsyncMultitonFactoryResolveOnCreateCalledCorrectly()
+    {
+        IocContainer container = new();
+        container.Register(r => r.AddMultiton<ITest, MultitonTest, int>().OnCreateAsync(t => t.Initialize()).WithFactory<IMultitonTestFactory>());
+        
+        IMultitonTestFactory testFactory = container.Resolve<IMultitonTestFactory>();
+        ITest test1 = await testFactory.Create(1);
+        ITest test2 = await testFactory.Create(2);
+        ITest anotherTest1 = await testFactory.Create(1);
+        
+        Assert.IsInstanceOf<Test>(test1);
+        Assert.That(test1.IsInitialized, Is.True);
+        
+        Assert.IsInstanceOf<Test>(test2);
+        Assert.That(test2.IsInitialized, Is.True);
+
+        Assert.AreSame(test1, anotherTest1);
+    }
+}

Test.LightweightIocContainer/OnCreateTest.cs

@@ -21,6 +21,7 @@ public class OnCreateTest
     private class Test : ITest
     {
         public void DoSomething() => throw new Exception();
+        public Task InitializeAsync() => throw new Exception();
     }
 
         
@@ -34,4 +35,15 @@ public class OnCreateTest
 
         Assert.Throws<Exception>(() => testRegistration.OnCreateAction!(test));
     }
+    
+    [Test]
+    public void TestOnCreateAsync()
+    {
+        RegistrationFactory registrationFactory = new(Substitute.For<IocContainer>());
+        ITypedRegistration<ITest, Test> testRegistration = registrationFactory.Register<ITest, Test>(Lifestyle.Transient).OnCreateAsync(t => t.InitializeAsync());
+
+        Test test = new();
+
+        Assert.Throws<Exception>(() => testRegistration.OnCreateActionAsync!(test));
+    }
 }