dotnetjunkie
commented
10 months ago I'm afraid this is a bug I can't fix. Fixing this quite radically changes the way Simple Injector works. Basically, the problem can be demonstrated with the following code:
var comObject = new Inventor.Application();
Type consumer = typeof(Foo<Inventor.Application>);
var ctor = consumer.GetConstructors().Single();
var param = ctor.GetParameters().Single();
var comExpr = Expression.Constant(comObject);
Expression.New(ctor, comExpr);
public record Foo<T>(T instance) { }When Inventor.Application would be any 'normal' .NET type, this code would complete successfully. With Inventor.Application being a COM object, you'll experience the following exception when Expression.New is called:
System.ArgumentException: Expression of type 'System.__ComObject' cannot be used for constructor parameter of type 'Inventor.Application'
Notice, BTW, how this code is pure .NET code. It runs without Simple Injector.
This exception is caused by a limitation in System.Linq.Expressions, which was never designed to properly handle COM objects. The problem occurs because both Expression.New and Expression.Constant do simple type checks that don't work with COM objects, and they don't check whether the supplied type is a COM object. This makes System.Linq.Expressions believe that the object doesn't match, which -in fact- it does. This is because proxy classes are generated by (I believe) the JIT in order to let .NET code communicate with the COM object.
Although it's not impossible for Simple Injector to work around this limitation of the .NET framework, this is not an investment I'm willing to make. Not only is this an enormous undertaking for a corner case scenario, more importantly, it forces me to make breaking changes to the API of Simple Injector—something I never take lightly.
You can expect other DI Containers to have similar limitations, especially the one's that are more optimized. Chances are slim, for instance, that this would work with MS.DI.
Not all is lost, though. Simple workarounds exist.
I'd like to propose a workaround, which is to make the COM object accessible through a 'provider' class or abstraction and to inject that provider instead of injecting the COM object directly. For instance:
// Application:
public sealed record AutodeskProvider(Inventor.Application Application);
public class UserInterfaceManager : IUserInterfaceManager
{
// Inject IAutodeskProvider instead of Inventor.Application
public UserInterfaceManager(AutodeskProvider provider) ...
}// Composition Root
// Register AutodeskProvider instead of Inventor.Application.
container.RegisterInstance(new AutodeskProvider(new Inventor.Application()));This works, because the COM object is no longer part of the constructor signature that is being constructed by Simple Injector and compiled by .NET.
myth384
Describe the bug
I am integrating Simple Injector into an AddIn-type application for Autodesk Inventor. Inventor exposes its API through COM interop. The primary entry point is a COM interface named Inventor.Application. Contrary to its name, this is indeed an interface, not a class. The Application instance gets successfully registered in the container using: container.RegisterInstance(inventor). Subsequently, the instance is retrieved successfully with: var inventor = container.GetInstance();. However, when the COM interface is utilized in the constructors of services, an exception is thrown upon calling container.Verify().
Expected behavior
I expect the Application instance to be injected into services.
Actual behavior
Instead the following exception is thrown:
To Reproduce
As I assume you may not have access to an Autodesk Inventor installation, the steps below can help simulate my situation: 1) Create a Console app. 2) Instantiate or obtain a COM object in this app. (Although I am not sure how...) 3) Create a class with a method that has a COM interface parameter. 4) Within this method, create a new Container instance. 5) Register the COM object using:
container.RegisterInstance(comInstance)6) Add a line to verify the container using:container.Verify()7) Create a class implementing an interface and add the COM interface to its constructor. 8) Register the interface and class using:container.Register<IService, Service>()9) After execution, the .Verify() call should throw an exception.Additional context
If you require any assistance, I am more that glad to help you out!