I am looking for some help with a simple "Hello World" example of DI. What I don't understand is how to initialize the classes "Foo" and "Bar" within a DI framework (autofac).
namespace AutofacTesting
{
//these classes are intended to be used with autofac / DI
public interface IFooBar
{
void Draw();
}
public class Bar : IFooBar
{
public void Draw()
{
MessageBox.Show("Drawing something in Bar");
}
}
public class Foo : IFooBar
{
public void Draw()
{
MessageBox.Show("Drawing somthing in Foo");
}
}
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
var builder = new ContainerBuilder();
builder.RegisterType<Bar>().As<IFooBar>();
builder.RegisterType<Foo>().As<IFooBar>();
var container = builder.Build();
var taskController = container.Resolve<IFooBar>();
taskController.Draw();
int a = 1;
}
}
}
I think you mean you want to resolve a Bar or Foo class as the concrete implementation, not instantiate it. If so you could write:
var builder = new ContainerBuilder();
builder.RegisterType<Bar>().Named<IFooBar>("Bar");
builder.RegisterType<Foo>().Named<IFooBar>("Foo");
var container = builder.Build();
var taskController = container.ResolveNamed<IFooBar>("Bar");
taskController.Draw();
I also realize this is a hello world application, but be careful not to fail into the anti-pattern of using a service locator (i.e. using contain.Resolve all over the place). Instead, consider designs which will allow you to have all the registration and resolving happen in the same place, named a composition root.
I mention this caution becuase having this level of ambiguity (i.e. multiple concreate types being registered for a given interface) can cause one to start using the service locator pattern. Instead, in more complex applications, consider refactoring your API to have less ambiguity upon resolving registered types.
Following on from this question I would like autofac to inject the type of the declaring object into the constructor of my NLog service, so that it can correctly log which type is logging entries.
My NLogService class looks like this...
public class NLogService : ILogService
{
private readonly Logger _logger;
public NLogService(Type t)
{
var consumerType = t.DeclaringType.FullName;
_logger = LogManager.GetLogger(consumerType);
}
However it fails on app startup because it obviously cannot work out what to inject into the constructor of the NLogService with the following error...
None of the constructors found with
'Public binding flags' on type
'MyProduct.Domain.Services.Logging.NLogService'
can be invoked with the available
services and parameters: Cannot
resolve parameter 'System.Type t' of
constructor 'Void .ctor(System.Type)'.
So, my question is - how do i instruct autofac to inject the type of the calling class?
I tried this...
public NLogService(Type t)
{
var method = MethodBase.GetCurrentMethod();
Type consumingType = method.DeclaringType;
var consumerType = consumingType.FullName;
var consumerType = t.DeclaringType.FullName;
_logger = LogManager.GetLogger(consumerType);
}
But i just end up with MyProduct.Domain.Services.Logging.NLogService
What i want is the type of the class that is doing the actual logging.
i have already tried this suggestion and it didnt work for me either.
Could make your NLogService generic, i.e. NLogService<T> and use Autofac's open generics support?
Then you could do this:
public class NLogService<T> : ILogger<T>
{
private readonly Logger _logger;
public NLogService()
{
_logger = LogManager.GetLogger(typeof(T).FullName);
}
}
There is no real good way to do this with Autofac, because does not have support for 'context based injection' (which is what you are trying to do). There is a workaround, but it aint pretty...
What you can do is revert to property injection and define a base class or interface for that ILogService property. For instance, you can define the following interface:
public interface ILoggerContainer
{
public ILogService Logger { get; set; }
}
Now you can implement this interface on all types that need a logger:
public class Consumer : IConsumer, ILoggerContainer
{
public ILogService Logger { get; set; }
}
With this in place you can configure Autofac as follows:
builder.RegisterType<ILoggerContainer>()
.OnActivating(e =>
{
var type = typeof(LogService<>)
.MakeGenericType(e.Instance.GetType());
e.Instance.Logger = e.Context.Resolve(type);
});
Another workaround, that you may find cleaner is to inject an ILogger<T> with the same type as the type of the parent type:
public class Consumer : IConsumer
{
public Consumer(ILogger<Consumer> logger) { }
}
This makes the configuration much easier and prevents you from having to have a base class. Which one is most appropriate is up to you.
As I said, these are workarounds, but to be honest, you might need to reconsider your logging strategy in your application. Perhaps you are logging at too many places. In the applications I write there is hardly ever a need to log, and when I do, I write an logging message that is expressive enough so that there is no need to communicate the type that triggered the event. And when you log exception, you will always have a complete stack trace (and exception logging should almost only happen in the outer layer of your application and not within services anyway).
The following technique works well in our experience:
Create an attribute like below, which can be applied at class level or at the injection site:
[AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Class)]
public class LoggerAttribute : Attribute
{
public readonly string Name;
public LoggerAttribute(string name)
{
Name = name;
}
}
Create an Autofac module that you register with the ContainerBuilder:
public class LogInjectionModule : Module
{
protected override void AttachToComponentRegistration(IComponentRegistry registry, IComponentRegistration registration)
{
registration.Preparing += OnComponentPreparing;
}
static void OnComponentPreparing(object sender, PreparingEventArgs e)
{
var typePreparing = e.Component.Activator.LimitType;
// By default, the name supplied to the logging instance is the name of the type in which it is being injected into.
string loggerName = typePreparing.FullName;
//If there is a class-level logger attribute, then promote its supplied name value instead as the logger name to use.
var loggerAttribute = (LoggerAttribute)typePreparing.GetCustomAttributes(typeof(LoggerAttribute), true).FirstOrDefault();
if (loggerAttribute != null)
{
loggerName = loggerAttribute.Name;
}
e.Parameters = e.Parameters.Union(new Parameter[]
{
new ResolvedParameter(
(p, i) => p.ParameterType == typeof (Logger),
(p, i) =>
{
// If the parameter being injected has its own logger attribute, then promote its name value instead as the logger name to use.
loggerAttribute = (LoggerAttribute)
p.GetCustomAttributes(typeof(LoggerAttribute),true).FirstOrDefault();
if (loggerAttribute != null)
{
loggerName = loggerAttribute.Name;
}
// Return a new Logger instance for injection, parameterised with the most appropriate name which we have determined above.
return LogManager.GetLogger(loggerName);
}),
// Always make an unamed instance of Logger available for use in delegate-based registration e.g.: Register((c,p) => new Foo(p.TypedAs<Logger>())
new TypedParameter(typeof(Logger), LogManager.GetLogger(loggerName))
});
}
}
You can now inject a named Logger in any one of these ways depending on individual scenarios:
By default, the injected logger name will be given the full type name of the class it is injected into:
public class Foo
{
public Foo(Logger logger)
{
}
}
Use a constructor parameter [Logger] attribute to override the logger name:
public class Foo
{
public Foo([Logger("Meaningful Name")]Logger logger)
{
}
}
Use a class-level [Logger] attribute to set the same logger name override for all constructor overloads:
[Logger("Meaningful Name")]
public class Foo
{
public Foo(Logger logger, int something)
{
}
public Foo(Logger logger, int something, DateTime somethingElse)
{
}
}
Use constructor parameter [Logger] attributes on each constructor overload to set different logger names depending on the context of how you were constructed:
public class Foo
{
public Foo(Logger("Meaningful Name")]Logger logger, int something)
{
}
public Foo(Logger("Different Name")]Logger logger, int something, DateTime somethingElse)
{
}
}
IMPORTANT NOTE: If you register types to be resolved with logger constructor injection using Autofac's delegate registration, you MUST use the two parameter overload like so: Register((c,p) => new Foo(p.TypedAs<Logger>()).
Hope this helps!
It is possible to do this without generics.
However, please note that in Autofac 6.x, the resolution process has changed to use a resolve pipeline. This doesn't matter for most scenarios, but it does when you want to use the lifetime events like OnPreparing, etc. Most of the answers here on SO around overriding the Preparing event are very old and are now outdated. You can't override Preparing directly anymore.
There is an example on the Autofac documentation site doing this for log4net, and it works with NLog with only minor changes. Here is the basic idea:
public class Log4NetMiddleware : IResolveMiddleware
{
public PipelinePhase Phase => PipelinePhase.ParameterSelection;
public void Execute(ResolveRequestContext context, Action<ResolveRequestContext> next)
{
// Add our parameters.
context.ChangeParameters(context.Parameters.Union(
new[]
{
new ResolvedParameter(
(p, i) => p.ParameterType == typeof(ILog),
(p, i) => LogManager.GetLogger(p.Member.DeclaringType)
),
}));
// Continue the resolve.
next(context);
// Has an instance been activated?
if (context.NewInstanceActivated)
{
var instanceType = context.Instance.GetType();
// Get all the injectable properties to set.
// If you wanted to ensure the properties were only UNSET properties,
// here's where you'd do it.
var properties = instanceType
.GetProperties(BindingFlags.Public | BindingFlags.Instance)
.Where(p => p.PropertyType == typeof(ILog) && p.CanWrite && p.GetIndexParameters().Length == 0);
// Set the properties located.
foreach (var propToSet in properties)
{
propToSet.SetValue(context.Instance, LogManager.GetLogger(instanceType), null);
}
}
}
}
Please also note that you have to understand how middleware works in Autofac. The documentation is a good place to start.
I can do this in Castle Windsor:
public abstract class AbstractFactory
{
protected AbstractFactory(Foo constructorParm)
{
// Do something with parameter...
}
}
public class DescendentFactory : AbstractFactory
{
public DescendentFactory(Foo constructorParm) : base(constructorParm)
{
}
}
// The container is configured via XML, the service AbstractFactory and the
// type DescendentFactory
container.Resolve<AbstractFactory>("DescendentFactoryId", new { constructorParm = injectedValue });
Is this possible in Unity? I've tried doing it but it complains that it can't find the constructor. It seems I can only inject via the sub-type.
You can only inject via the sub-type. It needs a public constructor.
How do I handle classes with static methods with Ninject?
That is, in C# one can not have static methods in an interface, and Ninject works on the basis of using interfaces?
My use case is a class that I would like it to have a static method to create an
unpopulated instance of itself.
EDIT 1
Just to add an example in the TopologyImp class, in the GetRootNodes() method, how would I create some iNode classes to return? Would I construct these with normal code practice or would I somehow use Ninject? But if I use the container to create then haven't I given this library knowledge of the IOC then?
public interface ITopology
{
List<INode> GetRootNodes();
}
public class TopologyImp : ITopology
{
public List<INode> GetRootNodes()
{
List<INode> result = new List<INode>();
// Need code here to create some instances, but how to without knowledge of the container?
// e.g. want to create a few INode instances and add them to the list and then return the list
}
}
public interface INode
{
// Parameters
long Id { get; set; }
string Name { get; set; }
}
class NodeImp : INode
{
public long Id
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
public string Name
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
}
// Just background to highlight the fact I'm using Ninject fine to inject ITopology
public partial class Form1 : Form
{
private ITopology _top;
public Form1()
{
IKernel kernal = new StandardKernel(new TopologyModule());
_top = kernal.Get<ITopology>();
InitializeComponent();
}
}
If you're building a singleton or something of that nature and trying to inject dependencies, typically you instead write your code as a normal class, without trying to put in lots of (probably incorrect) code managing the singleton and instead register the object InSingletonScope (v2 - you didnt mention your Ninject version). Each time you do that, you have one less class that doesnt surface its dependencies.
If you're feeling especially bloody-minded and are certain that you want to go against that general flow, the main tools Ninject gives you is Kernel.Inject, which one can use after you (or someone else) has newd up an instance to inject the dependencies. But then to locate one's Kernelm you're typically going to be using a Service Locator, which is likely to cause as much of a mess as it is likely to solve.
EDIT: Thanks for following up - I see what you're after. Here's a hacky way to approximate the autofac automatic factory mechanism :-
/// <summary>
/// Ugly example of a not-very-automatic factory in Ninject
/// </summary>
class AutomaticFactoriesInNinject
{
class Node
{
}
class NodeFactory
{
public NodeFactory( Func<Node> createNode )
{
_createNode = createNode;
}
Func<Node> _createNode;
public Node GenerateTree()
{
return _createNode();
}
}
internal class Module : NinjectModule
{
public override void Load()
{
Bind<Func<Node>>().ToMethod( context => () => Kernel.Get<Node>() );
}
}
[Fact]
public void CanGenerate()
{
var kernel = new StandardKernel( new Module() );
var result = kernel.Get<NodeFactory>().GenerateTree();
Assert.IsType<Node>( result );
}
}
The ToMethod stuff is a specific application of the ToProvider pattern -- here's how you'd do the same thing via that route:-
...
class NodeProvider : IProvider
{
public Type Type
{
get { return typeof(Node); }
}
public object Create( IContext context )
{
return context.Kernel.Get<Node>();
}
}
internal class Module : NinjectModule
{
public override void Load()
{
Bind<Func<Node>>().ToProvider<NodeProvider>();
}
}
...
I have not thought this through though and am not recommending this as A Good Idea - there may be far better ways of structuring something like this. #Mark Seemann? :P
I believe Unity and MEF also support things in this direction (keywords: automatic factory, Func)
EDIT 2: Shorter syntax if you're willing to use container-specific attributes and drop to property injection (even if Ninject allows you to override the specific attributes, I much prefer constructor injection):
class NodeFactory
{
[Inject]
public Func<Node> NodeFactory { private get; set; }
public Node GenerateTree()
{
return NodeFactory();
}
}
EDIT 3: You also need to be aware of this Ninject Module by #Remo Gloor which is slated to be in the 2.4 release
EDIT 4: Also overlapping, but not directly relevant is the fact that in Ninject, you can request an IKernel in your ctor/properties and have that injected (but that doesn't work directly in a static method).
I'm trying to use StructureMap with nServiceBus.
The Project:
Uses a GenericHost Endpoint to send command messages
Configures nServiceBus using the StructMapBuilder.
Uses a simple StructureMap registry config
Uses a start up class TestServer supporting IWantToRunAtStartup
The TestServer class has ctor dependency on a TestManager class
The TestManager class has ctor dependency on IBus
ObjectFactory.WhatDoIHave() shows StructureMap knows how to construct the classes.
When run I get buildup errors. nServiceBus seems to be overwriting the config?
Note that when I add a IBus ctor depenendency to my event handlers without any other config all appears fine.
Error:
Exception when starting endpoint, error has been logged. Reason: Error creating object with name 'nSeviceBusStructureMapTest.TestServer' : Unsatisfied dependency expressed through constructor argument with index 0 of type [nSeviceBusStructureMapTest.ITestManager] : No unique object of type [nSeviceBusStructureMapTest.ITestManager] is defined : Unsatisfied dependency of type [nSeviceBusStructureMapTest.ITestManager]: expected at least 1 matching object to wire the [miningServiceManage] parameter on the constructor of object [nSeviceBusStructureMapTest.TestServer]
Source:
using System;
using System.Diagnostics;
using NServiceBus;
using StructureMap;
using StructureMap.Configuration.DSL;
namespace nSeviceBusStructureMapTest
{
public class TestSmRegistry : Registry
{
public TestSmRegistry()
{
For<ITestManager>().Use<TestManager>();
For<TestServer>().Use<TestServer>();
}
}
public class TestEndPoint : AsA_Server, IConfigureThisEndpoint
{
public void Init()
{
Configure.With().StructureMapBuilder(ObjectFactory.Container);
ObjectFactory.Configure(c => c.AddRegistry<TestSmRegistry>());
Debug.WriteLine(ObjectFactory.WhatDoIHave());
}
}
public class TestServer : IWantToRunAtStartup
{
public TestServer(ITestManager miningServiceManage)
{
_miningServiceManage = miningServiceManage;
}
private readonly ITestManager _miningServiceManage;
public void Run()
{
_miningServiceManage.Run();
}
public void Stop() { }
}
public interface ITestManager
{
void Run();
}
public class TestManager : ITestManager
{
public TestManager(IBus bus)
{
_bus = bus;
}
private readonly IBus _bus;
public void Run()
{
if (_bus == null) Debug.WriteLine("Error no bus");
// Send messages on bus;
}
}
}
<MsmqTransportConfig InputQueue="test" ErrorQueue="error" NumberOfWorkerThreads="1" MaxRetries="5" />
<UnicastBusConfig>
<MessageEndpointMappings>
</MessageEndpointMappings>
</UnicastBusConfig>
Any ideas?
You have to specify IWantCustomInitialization on the endpoint config class. Otherwise NServiceBus won't call the Init() method. You also need to specify what serializer to use so add:
Configure.With()
.StructureMapBuilder()
.XmlSerializer();
Hope this helps!