Autofac and injection of instances - asp.net-mvc

Question

In a ASP.NET MVC project I'm working on I have the following piece of code that basically inject instances to specific methods within my assemblies.
So in the application root I have a class that register the instances like this and finally handles the injection.
ApplicationServiceProvider serviceProvider = ApplicationServiceProvider.CreateDefaultProvider();
serviceProvider.RegisterInstance(GlobalConfiguration.Configuration);
serviceProvider.RegisterInstance(GlobalFilters.Filters);
serviceProvider.RegisterInstance(RouteTable.Routes);
serviceProvider.RegisterInstance(BundleTable.Bundles);
serviceProvider.Distribute();
Now when I want to access these instances from the assemblies, I have to create some handler (method) and mark it with the following attribute 'ApplicationServiceHandler' like in the following example.
[ContractVerification(false)]
public static class RouteConfiguration
{
[ApplicationServiceHandler]
public static void Register(RouteCollection routes)
{
}
}
This is part of the extensibility layer in the project which is currently working pretty good.
Now, I'm new to Autofac and I wonder whether I can use Autofac to do the work for me rather than using my own implementation (which I provided below) that probably does it less efficient and handles less cases that are already covered by Autofac.
I noticed Autofac have a RegisterInstance method but I'm not sure how to tell it to inject the instances to methods flagged with 'ApplicationServiceHandler' attribute, I'm not not sure it's even the correct method but based on the name it seems like the right one.
Any kind of help is greatly appreciated, thank you.
EDIT: Here is the code that I'm using to achieve this without Autofac in my project.
ApplicationServiceHandlerAttribute.cs
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class ApplicationServiceHandlerAttribute : Attribute
{
}
ApplicationServiceHandler.cs
public sealed class ApplicationServiceHandler
{
private readonly MethodInfo _method;
private readonly object[] _args;
public ApplicationServiceHandler(MethodInfo method, object[] args)
{
Contract.Requires(method != null);
Contract.Requires(args != null);
_method = method;
_args = args;
}
public void Invoke()
{
_method.Invoke(null, _args);
}
[ContractInvariantMethod]
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification = "Required for code contracts.")]
private void ObjectInvariant()
{
Contract.Invariant(_method != null);
Contract.Invariant(_args != null);
}
}
ApplicationServiceProvider.cs
public sealed class ApplicationServiceProvider
{
private readonly IEnumerable<Assembly> _assemblies;
private readonly Dictionary<Type, object> _instances;
public ApplicationServiceProvider(IEnumerable<Assembly> assemblies)
{
Contract.Requires(assemblies != null);
_assemblies = assemblies;
_instances = new Dictionary<Type, object>();
}
public static ApplicationServiceProvider CreateDefaultProvider()
{
Contract.Ensures(Contract.Result<ApplicationServiceProvider>() != null);
return new ApplicationServiceProvider(PackageLoader.ReferencedAssemblies);
}
public void Distribute()
{
foreach (var handler in GetHandlers())
{
Contract.Assume(handler != null);
handler.Invoke();
}
}
public IEnumerable<ApplicationServiceHandler> GetHandlers()
{
Contract.Ensures(Contract.Result<IEnumerable<ApplicationServiceHandler>>() != null);
if (_instances.Count == 0)
{
yield break;
}
foreach (var asm in _assemblies)
{
IEnumerable<MethodInfo> methods = GetMethods(asm);
foreach (var method in methods)
{
ParameterInfo[] #params = method.GetParameters();
if (#params.Length > 0)
{
int instanceCount = 0;
object[] args = new object[#params.Length];
for (int i = 0; i < #params.Length; i++)
{
ParameterInfo param = #params[i];
var instance = GetInstance(param);
if (instance != null)
{
instanceCount++;
args[i] = instance;
}
}
if (instanceCount > 0)
{
yield return new ApplicationServiceHandler(method, args);
}
}
}
}
}
public bool RegisterInstance(object instance)
{
Contract.Requires(instance != null);
return AddInstance(instance);
}
private static ApplicationServiceHandlerAttribute GetApplicationServiceHandlerAttribute(MethodInfo method)
{
ApplicationServiceHandlerAttribute attribute = null;
try
{
attribute = method.GetCustomAttribute<ApplicationServiceHandlerAttribute>(false);
}
catch (TypeLoadException)
{
// We don't need to do anything here for now.
}
return attribute;
}
private static IEnumerable<Type> GetDefinedTypes(Assembly assembly)
{
Contract.Requires(assembly != null);
Contract.Ensures(Contract.Result<IEnumerable<Type>>() != null);
try
{
return assembly.DefinedTypes;
}
catch (ReflectionTypeLoadException ex)
{
return ex.Types.Where(type => type != null);
}
}
/// <summary>
/// Gets the methods that are marked with <see cref="ApplicationServiceHandlerAttribute"/> from the assembly.
/// </summary>
/// <remarks>
/// Eyal Shilony, 21/11/2012.
/// </remarks>
/// <param name="assembly">
/// The assembly.
/// </param>
/// <returns>
/// The methods that are marked with <see cref="ApplicationServiceHandlerAttribute"/> from the assembly.
/// </returns>
private static IEnumerable<MethodInfo> GetMethods(Assembly assembly)
{
Contract.Requires(assembly != null);
Contract.Ensures(Contract.Result<IEnumerable<MethodInfo>>() != null);
const TypeAttributes STATIC_TYPE_ATTRIBUTES = TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Sealed | TypeAttributes.BeforeFieldInit;
var methods = (from type in GetDefinedTypes(assembly)
where type.Attributes == STATIC_TYPE_ATTRIBUTES
from method in type.GetMethods().AsParallel()
where GetApplicationServiceHandlerAttribute(method) != null
select method).ToArray();
return methods;
}
private bool AddInstance(object instance)
{
Type type = instance.GetType();
return AddInstance(type, instance);
}
private bool AddInstance(Type type, object instance)
{
if (!_instances.ContainsKey(type))
{
_instances.Add(type, instance);
return true;
}
return false;
}
private object GetInstance(ParameterInfo param)
{
object instance = null;
Type paramType = param.ParameterType;
if (_instances.ContainsKey(paramType))
{
instance = _instances[paramType];
}
else
{
foreach (var type in _instances.Keys.Where(type => type.IsSubclassOf(paramType)))
{
instance = _instances[type];
break;
}
}
return instance;
}
}

Answer 1

i hope , i have understood you correctly.if what you mean is marking a class as dependency with attributes then you can do it by creating custom attribute.following is an example of implementing such an attribute :
public class DependencyAttribute : Attribute
{
public DependencyAttribute()
{
}
//The type of service the attributed class represents
public Type ServiceType { get; set; }
//Optional key to associate with the service
public string Key { get; set; }
public virtual void RegisterService(AttributeInfo<DependencyAttribute> attributeInfo, IContainer container)
{
Type serviceType = attributeInfo.Attribute.ServiceType ?? attributeInfo.DecoratedType;
Containerbuilder builder = new ContainerBuilder();
builder.RegisterType(attributeInfo.DecoratedType).As(serviceType).Keyed(
attributeInfo.Attribute.Key ?? attributeInfo.DecoratedType.FullName);
builder.Update(container)
}
}
then you must find all types marked with this attribute and call the RegisterService method of these attributes.
public class DependencyAttributeRegistrator
{
public DependencyAttributeRegistrator()
{
}
public IEnumerable<AttributeInfo<DependencyAttribute>> FindServices()
{
//replace this line with you'r own
var types = Assembly.GetExecutingAssembly().GetTypes();
foreach (Type type in types)
{
var attributes = type.GetCustomAttributes(typeof(DependencyAttribute), false);
foreach (DependencyAttribute attribute in attributes)
{
yield return new AttributeInfo<DependencyAttribute> { Attribute = attribute, DecoratedType = type };
}
}
}
public void RegisterServices(IEnumerable<AttributeInfo<DependencyAttribute>> services)
{
foreach (var info in services)
{
//replace following two line with you'r own global container
var builder = new ContainerBuilder();
IContainer container = builder.Build();
info.Attribute.RegisterService(info, container);
}
}
}