GeneratedComInterface/Class needs a way to register a factory method #111616
Description
In built in COM we had ExtensibleClassFactory.RegisterObjectCreationCallback where we could register a factory method (often in native code)
[ComImport, Guid(<guid1>)]
public interface IMyInterface
{
void DoStuff();
}
[ComImport, Guid(<guid2>)]
public class MyClassHelper : IMyInterface
{
[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType=MethodCodeType.Runtime)]
public virtual extern void DoStuff();
}
[Guid(<guid2>)]
public class MyClass : MyClassHelper
{
static MyClass()
{
ExtensibleClassFactory.RegisterObjectCreationCallback(new ObjectCreationDelegate(CreateComInstanceDelegate));
}
private static IntPtr CreateComInstanceDelegate(IntPtr aggr)
{
return NativeMethods.CreateComInstance(typeof(MyClass).Guid);
}
}
// usage
var inst = new MyClass();
inst.DoStuff();in source generated COM I can do:
[GeneratedComInterface, Guid(<guid1>)]
public interface IMyInterface
{
void DoStuff();
}
// usage
var ptr = NativeMethods.CreateComInstance(typeof(MyClass).Guid);
var inst = ComInterfaceMarshaller<IMyInterface>.ConvertToManaged(ptr);
inst.DoStuff();which is not as straight forward as before.
Instead I can use the decorator pattern:
[GeneratedComClass, Guid(<guid2>)]
public class MyClass : IMyInterface
{
private IMyInterface _inner;
public MyClass()
{
var ptr = NativeMethods.CreateComInstance(typeof(MyClass).Guid);
_inner = ComInterfaceMarshaller<IMyInterface>.ConvertToManaged(ptr);
}
public void DoStuff() => _inner.DoStuff();
}
// usage
var inst = new MyClass();
inst.DoStuff();I know I can probably write a source generator that does exactly that but it will be great if the default tooling could do that for us.
something like:
[GeneratedComClassWrapper(typeof(IMyInterface)), Guid(<guid2>)]
public class MyClass
{
static MyClass()
{
RegisterObjectCreationCallback(static _ => NativeMethods.CreateComInstance(typeof(MyClass).Guid));
}
}
// usage
var inst = new MyClass();
inst.DoStuff();This would help migrating dotnet framework code that make heavy use of builtin COM interop.
EDIT: fixed declaration of _inner