Trouble casting CoCreateInstance of an object that implements a Vanara interface

[catmanjan]

Hello I have a class which implements IStorageProviderHandler, when I run the following code for other such classes it works, but when I use my CLSID I get an error: System.InvalidCastException: 'Unable to cast object of type 'IngressStorageProviderHandler.StorageProviderHandler' to type 'IStorageProviderHandler'.'

Here is the code:

var myClassId = new Guid("{2d1275b6-7d67-454e-b204-4effb9ecb034}");
var interfaceIdOfIStorageProviderHandler = new Guid("{162C6FB5-44D3-435B-903D-E613FA093FB5}");
var ok = CoCreateInstance(myClassId, dwClsContext: CLSCTX.CLSCTX_ALL, riid: interfaceIdOfIStorageProviderHandler, ppv: out var comObject);

var type = comObject.GetType();

IStorageProviderHandler storageProviderHandler = (IStorageProviderHandler)comObject;

If I inspect type.ImlementedInterfaces I get a list of one which is: {Name = "IStorageProviderHandler" FullName = "Vanara.PInvoke.Shell32+IStorageProviderHandler"}

Perhaps there is another way to cast objects in this situation?

[dahall]

If you've created a class that inherits from IStorageProviderHandler, you can just new it to create an instance. You shouldn't use CoCreateInstance.

[catmanjan]

Unfortunately I need to support cocreateinstance, Microsoft Office is the one who is initialising my class (there's some explanation here https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/plus/sync-client/metadata ) For some reason my vanara implementation isn't working, so I was comparing it to a working one (C++) and the first thing I noticed was that the C++ version allows the cast to occur whereas vanara won't cast

…

On Sun, 14 Sept 2025, 8:25 am David Hall, ***@***.***> wrote: If you've created a class that inherits from IStorageProviderHandler, you can just new it to create an instance. You shouldn't use CoCreateInstance. — Reply to this email directly, view it on GitHub <#559 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABBRBRADG5ODVWBQ42DLM33SSKWLAVCNFSM6AAAAACGJVAR22VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTIMZZGM2DGMA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[dahall]

Does this work? It uses .NET RCW instead of direct COM.

Type comType = Type.GetTypeFromCLSID(new Guid("{2d1275b6-7d67-454e-b204-4effb9ecb034}"));
object comObject = Activator.CreateInstance(comType);
IStorageProviderHandler storageProviderHandler = (IStorageProviderHandler)comObject;