How to access methods or properties of a dispinterface object?

Question

How to access methods or properties of a dispinterface object?

Manoj 86

I have an object with type System.__ComObject. I found out that it implements an interface called _IContactsAndGroupsCallback which is present in the UCCollaborationLib namespace. As you can see in the link that it is a dispinterface. I confirmed that the object implements that interface by printing the result of objName is _IContactsAndGroupsCallback which is true. But when I try to typecast the object like this:

_IContactsAndGroupsCallback itf = (_IContactsAndGroupsCallback)objName;

I get an exception:

Exception thrown: 'System.InvalidCastException' in mscorlib.dll
An exception of type 'System.InvalidCastException' occurred in mscorlib.dll and wasn't handled before a managed/native boundary
Specified cast is not valid.

Details about the exception:

System.InvalidCastException  
  HResult=0x80004002  
  Message=Specified cast is not valid.  
  Source=mscorlib  
  StackTrace:  
   at System.Runtime.InteropServices.Marshal.GetIDispatchForObjectNative(Object o, Boolean onlyInContext)  
   at System.Runtime.InteropServices.DispatchWrapper..ctor(Object obj)  
   at System.RuntimeType.WrapArgsForInvokeCall(Object[] aArgs, Int32[] aWrapperTypes)  
   at System.RuntimeType.ForwardCallToInvokeMember(String memberName, BindingFlags flags, Object target, Int32[] aWrapperTypes, MessageData& msgData)  
   at UCCollaborationLib._IContactsAndGroupsCallback.OnLookup(ContactManager _source, Object _lookupResult, AsynchronousOperation _asyncOperation)  
   at OutlookPresenceProvider.IMClientContactManager.Lookup(String _lookupString, Object _contactsAndGroupsCallback, Object _state)

And when I try to access a method inside the _IContactsAndGroupsCallback interface like this:

objName.GetType().InvokeMember("OnLookup", BindingFlags.InvokeMethod, null, objName, new object[] { this, null, asyncOperation });

Then I get this exception:

System.Reflection.TargetInvocationException  
  HResult=0x80131604  
  Message=COM target does not implement IDispatch.  
  Source=mscorlib  
  StackTrace:  
   at System.RuntimeType.InvokeDispMethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture, String[] namedParameters)  
   at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)  
   at OutlookPresenceProvider.IMClientContactManager.Lookup(String _lookupString, Object _contactsAndGroupsCallback, Object _state)

How can I invoke the methods of a dispinterface object?

RLWA32 49,551 Reputation points

2022-03-07T16:41:49.283+00:00

This is a dispinterface. Its members define the event handlers for the events raised by object. To catch the events, an OCOM API client must implement these event handlers and advise the event source of the implementation if it is interested in to receive the events.

From the description of the interface it seems that your client needs to implement the methods of the interface in order to receive events after it advises an office application. What does the type library viewer (oleview.exe) show for this interface? Is the interface included in the object's COM registration? Do the MS docs indicate that this object can be instantiated with CoCreateInstance or is it only available through a call to a method on some object?

What happens if you cast your object to IDispatch instead of _IContactsAndGroupsCallback?

You may find this informative -- Dispatch interfaces as connection point interfaces
Manoj 86 Reputation points

2022-03-08T10:46:51.597+00:00
This is a dispinterface. Its members define the event handlers for the events raised by object. To catch the events, an OCOM API client must implement these event handlers.

This text that you copied from the docs is written about the dispinterface _IContactManagerEvents. We need to implement those event handlers if we want to catch the events raised by the object but we are not trying to do that. We just want to invoke its methods.

I am attaching the details shown by OleViewer for this interface.

Is the interface included in the object's COM registration? Do the MS docs indicate that this object can be instantiated with CoCreateInstance or is it only available through a call to a method on some object?

I am using this doc to detect presence in Outlook using my IM client app. I am trying to implement the IContactManager interface and I'm getting this COM object in the params for this function like this:

public AsynchronousOperation Lookup(string _lookupString, object _contactsAndGroupsCallback, object _state)

Manoj 86

If I cast the object to IDispatch instead of _IContactsAndGroupsCallback, then I get this exception

System.InvalidCastException
  HResult=0x80004002
  Message=Unable to cast COM object of type 'System.__ComObject' to interface type 'IDispatchInfo'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00020400-0000-0000-C000-000000000046}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
  Source=OutlookPresenceProvider
  StackTrace:
   at OutlookPresenceProvider.DispatchUtility.GetType(Object obj, Boolean throwIfNotFound)

RLWA32 49,551 Reputation points

2022-03-08T11:03:36.357+00:00

Well, it appears that there is an issue with the object that you have created to implement this interface. Without seeing the code I cannot provide any further diagnosis of the problem. Practically speaking I'm not sure how much further assistance I can render since I do not have the Office application installed on my system.
Manoj 86 Reputation points

2022-03-08T11:19:21.153+00:00

I did not create the object. I am just implementing the IContactManager interface and the Lookup method is being called by the Office application Outlook. So the object is being created and passed by Outlook. I can share the code with you if you want but to debug it, you'll have to install Outlook on your system.
Manoj 86 Reputation points

2022-03-08T11:48:44.773+00:00

Here is the code-
https://drive.google.com/file/d/12fmCU9NsiuGSNG6S6quS_xOeJugR6xO1/view?usp=sharing
RLWA32 49,551 Reputation points

2022-03-08T12:25:09.133+00:00

Sorry, installing Outlook is not an option for me.
Manoj 86 Reputation points

2022-03-08T12:53:47.407+00:00

It's okay.

If it's cool with you, you can take a look at the code and guide me on how I can solve this issue.
RLWA32 49,551 Reputation points

2022-03-08T13:29:54.9+00:00

Other than the skimpy Microsoft Documentation at integrating-im-applications-with-office I have no insight into the interactions between Outlook and an IM Client. Quite simply, I don't know anything about the implementation details and I am not in a position to acquire that knowledge. If I could provide guidance to you I would do so, but I can't in this instance. Again, sorry.
Manoj 86 Reputation points

2022-03-08T14:44:52.207+00:00

It's okay. No problem @RLWA32 . You've already helped me a lot in the past. Thank you for that.

1 answer

Your answer

RLWA32 49,551 Reputation points

2022-03-07T16:41:49.283+00:00

This is a dispinterface. Its members define the event handlers for the events raised by object. To catch the events, an OCOM API client must implement these event handlers and advise the event source of the implementation if it is interested in to receive the events.

From the description of the interface it seems that your client needs to implement the methods of the interface in order to receive events after it advises an office application. What does the type library viewer (oleview.exe) show for this interface? Is the interface included in the object's COM registration? Do the MS docs indicate that this object can be instantiated with CoCreateInstance or is it only available through a call to a method on some object?

What happens if you cast your object to IDispatch instead of _IContactsAndGroupsCallback?

You may find this informative -- Dispatch interfaces as connection point interfaces
Manoj 86 Reputation points

2022-03-08T10:46:51.597+00:00

This is a dispinterface. Its members define the event handlers for the events raised by object. To catch the events, an OCOM API client must implement these event handlers.

This text that you copied from the docs is written about the dispinterface _IContactManagerEvents. We need to implement those event handlers if we want to catch the events raised by the object but we are not trying to do that. We just want to invoke its methods.

I am attaching the details shown by OleViewer for this interface.

Is the interface included in the object's COM registration? Do the MS docs indicate that this object can be instantiated with CoCreateInstance or is it only available through a call to a method on some object?

I am using this doc to detect presence in Outlook using my IM client app. I am trying to implement the IContactManager interface and I'm getting this COM object in the params for this function like this:

public AsynchronousOperation Lookup(string _lookupString, object _contactsAndGroupsCallback, object _state)
Manoj 86 Reputation points

2022-03-08T10:51:51.337+00:00

If I cast the object to IDispatch instead of _IContactsAndGroupsCallback, then I get this exception

System.InvalidCastException HResult=0x80004002 Message=Unable to cast COM object of type 'System.__ComObject' to interface type 'IDispatchInfo'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00020400-0000-0000-C000-000000000046}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)). Source=OutlookPresenceProvider StackTrace: at OutlookPresenceProvider.DispatchUtility.GetType(Object obj, Boolean throwIfNotFound)
RLWA32 49,551 Reputation points

2022-03-08T11:03:36.357+00:00

Well, it appears that there is an issue with the object that you have created to implement this interface. Without seeing the code I cannot provide any further diagnosis of the problem. Practically speaking I'm not sure how much further assistance I can render since I do not have the Office application installed on my system.
Manoj 86 Reputation points

2022-03-08T11:19:21.153+00:00

I did not create the object. I am just implementing the IContactManager interface and the Lookup method is being called by the Office application Outlook. So the object is being created and passed by Outlook. I can share the code with you if you want but to debug it, you'll have to install Outlook on your system.
Manoj 86 Reputation points

2022-03-08T11:48:44.773+00:00

Here is the code-
https://drive.google.com/file/d/12fmCU9NsiuGSNG6S6quS_xOeJugR6xO1/view?usp=sharing
RLWA32 49,551 Reputation points

2022-03-08T12:25:09.133+00:00

Sorry, installing Outlook is not an option for me.
Manoj 86 Reputation points

2022-03-08T12:53:47.407+00:00

It's okay.

If it's cool with you, you can take a look at the code and guide me on how I can solve this issue.
RLWA32 49,551 Reputation points

2022-03-08T13:29:54.9+00:00

Other than the skimpy Microsoft Documentation at integrating-im-applications-with-office I have no insight into the interactions between Outlook and an IM Client. Quite simply, I don't know anything about the implementation details and I am not in a position to acquire that knowledge. If I could provide guidance to you I would do so, but I can't in this instance. Again, sorry.
Manoj 86 Reputation points

2022-03-08T14:44:52.207+00:00

It's okay. No problem @RLWA32 . You've already helped me a lot in the past. Thank you for that.

Answer 1

Bruce (SqlWork.com) 77,926 Volunteer Moderator

you need to create a com wrapper for the .net code you want to pass to the com object.

https://learn.microsoft.com/en-us/dotnet/standard/native-interop/cominterop

Manoj 86 Reputation points

2022-03-08T11:06:22.747+00:00

Do you mean that the arguments that I'm passing to the "OnLookup" method of the object need to be wrapped in a COM wrapper? If yes, I think that the error I'm getting would be different if this was the issue.

Share via

How to access methods or properties of a dispinterface object?

1 answer

Your answer