C# COM server events "lost" when raising events while Excel is in edit mode

Question

I posted this question on StackOverflow (http://stackoverflow.com/questions/23798443/c-sharp-com-server-events-lost-when-raising-events-while-excel-is-in-edit-mode) but did not receive a good answer, so I'm trying my luck here.
I have an in-proc COM server written in C# (using .NET Framework 3.5) that raises COM events based on this example: http://msdn.microsoft.com/en-us/library/dd8bf0x3(v=vs.90).aspx
Excel VBA is the most common client of my COM server.  I’ve found that when I raise COM events while Excel is in edit mode (e.g. a cell is being edited) the event is “lost”.  Meaning, the VBA event handler is never called (even after the Excel
edit mode is finished) and the call to the C# event delegate passes through and fails silently with no exceptions being thrown.  Do you know how I can detect this situation on my COM server?  Or better still, make the event delegate call block until
Excel is out of edit mode?
I have tried:
Inspecting the properties of the event delegate – could not find any property to indicate that the event failed to be raised on the client.
Calling the event delegate directly from a worker thread and from the main thread – event not raised on the client, no exceptions thrown on the server.
Pushing the event delegate onto a worker thread’s Dispatcher and invoking it synchronously – event not raised on the client, no exceptions thrown on the server.
Pushing the event delegate onto the main thread’s Dispatcher and invoking it synchronously and asynchronously – event not raised on the client, no exceptions thrown on the server.
Checking the status code of the Dispatcher.BeginInvoke call (using DispatcherOperation.Status) – the status is always ends with “Completed”, and is never in “Aborted” state.
Creating an out-of-proc C# COM server exe and tested raising the events from there – same result, event handler never called, no exceptions.
Since I get no indication that the event was not raised on the client, I cannot handle this situation in my code.
I have tested this with Excel 2010 and Excel 2013.
Here is a simple test case.  The C# COM server:
namespace ComServerTest
public delegate void EventOneDelegate();
// Interface
[Guid("2B2C1A74-248D-48B0-ACB0-3EE94223BDD3"), Description("ManagerClass interface")]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
[ComVisible(true)]
public interface IManagerClass
[DispId(1), Description("Describes MethodAAA")]
String MethodAAA(String strValue);
[DispId(2), Description("Start thread work")]
String StartThreadWork(String strIn);
[DispId(3), Description("Stop thread work")]
String StopThreadWork(String strIn);
[Guid("596AEB63-33C1-4CFD-8C9F-5BEF17D4C7AC"), Description("Manager events interface")]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
[ComVisible(true)]
public interface ManagerEvents
[DispId(1), Description("Event one")]
void EventOne();
[Guid("4D0A42CB-A950-4422-A8F0-3A714EBA3EC7"), Description("ManagerClass implementation")]
[ComVisible(true), ClassInterface(ClassInterfaceType.None)]
[ComSourceInterfaces(typeof(ManagerEvents))]
public class ManagerClass : IManagerClass
private event EventOneDelegate EventOne;
private System.Threading.Thread m_workerThread;
private bool m_doWork;
private System.Windows.Threading.Dispatcher MainThreadDispatcher = null;
public ManagerClass()
// Assumes this is created on the main thread
MainThreadDispatcher = System.Windows.Threading.Dispatcher.CurrentDispatcher;
m_doWork = false;
m_workerThread = new System.Threading.Thread(DoThreadWork);
// Simple thread that raises an event every few seconds
private void DoThreadWork()
DateTime dtStart = DateTime.Now;
TimeSpan fiveSecs = new TimeSpan(0, 0, 5);
while (m_doWork)
if ((DateTime.Now - dtStart) > fiveSecs)
System.Diagnostics.Debug.Print("Raising event...");
try
if (EventOne != null)
// Tried calling the event delegate directly
EventOne();
// Tried synchronously invoking the event delegate from the main thread's dispatcher
MainThreadDispatcher.Invoke(EventOne, new object[] { });
// Tried asynchronously invoking the event delegate from the main thread's dispatcher
System.Windows.Threading.DispatcherOperation dispOp = MainThreadDispatcher.BeginInvoke(EventOne, new object[] { });
// Tried synchronously invoking the event delegate from the worker thread's dispatcher.
// Asynchronously invoking the event delegate from the worker thread's dispatcher did not work regardless of whether Excel is in edit mode or not.
System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke(EventOne, new object[] { });
catch (System.Exception ex)
// No exceptions were thrown when attempting to raise the event when Excel is in edit mode
System.Diagnostics.Debug.Print(ex.ToString());
dtStart = DateTime.Now;
// Method should be called from the main thread
[ComVisible(true), Description("Implements MethodAAA")]
public String MethodAAA(String strValue)
if (EventOne != null)
try
// Tried calling the event delegate directly
EventOne();
// Tried asynchronously invoking the event delegate from the main thread's dispatcher
System.Windows.Threading.DispatcherOperation dispOp = System.Windows.Threading.Dispatcher.CurrentDispatcher.BeginInvoke(EventOne, new object[] { });
// Tried synchronously invoking the event delegate from the main thread's dispatcher
System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke(EventOne, new object[] { });
catch (System.Exception ex)
// No exceptions were thrown when attempting to raise the event when Excel is in edit mode
System.Diagnostics.Debug.Print(ex.ToString());
return "";
return "";
[ComVisible(true), Description("Start thread work")]
public String StartThreadWork(String strIn)
m_doWork = true;
m_workerThread.Start();
return "";
[ComVisible(true), Description("Stop thread work")]
public String StopThreadWork(String strIn)
m_doWork = false;
m_workerThread.Join();
return "";
I register it using regasm:
%SystemRoot%\Microsoft.NET\Framework\v2.0.50727\regasm /codebase ComServerTest.dll /tlb:ComServerTest.tlb
Excel VBA client code:
Public WithEvents managerObj As ComServerTest.ManagerClass
Public g_nCounter As Long
Sub TestEventsFromWorkerThread()
Set managerObj = New ComServerTest.ManagerClass
Dim dtStart As Date
dtStart = DateTime.Now
g_nCounter = 0
Debug.Print "Start"
' Starts the worker thread which will raise the EventOne event every few seconds
managerObj.StartThreadWork ""
Do While True
DoEvents
' Loop for 20 secs
If ((DateTime.Now - dtStart) * 24 * 60 * 60) > 20 Then
' Stops the worker thread
managerObj.StopThreadWork ""
Exit Do
End If
Loop
Debug.Print "Done"
End Sub
Sub TestEventFromMainThread()
Set managerObj = New ComServerTest.ManagerClass
Debug.Print "Start"
' This call will raise the EventOne event
managerObj.MethodAAA ""
Debug.Print "Done"
End Sub
' EventOne handler
Private Sub managerObj_EventOne()
Debug.Print "EventOne " & g_nCounter
g_nCounter = g_nCounter + 1
End Sub
This problem also occurs for a C++ MFC Automation server that raises COM events.  If I raise the COM event from the main thread when Excel is in edit mode, the event handler is never called.  No errors or exceptions are thrown on the server,
similar to my C# COM server.  However, if I use the Global Interface Table to marshal the event sink interface from the main thread
back to the main thread, then invoking the event - it will block while Excel is in edit mode.  (I also used COleMessageFilter to disable the busy dialog and not responding dialogs, otherwise I'd receive the exception:
RPC_E_CANTCALLOUT_INEXTERNALCALL It is illegal to call out while inside message filter.)
Knowing that, I tried to do the same on my C# COM server.  I could instantiate the Global Interface Table (using the definition from pinvoke.net) and the message filter (using the IOleMessageFilter definition from MSDN).  However, the event still
gets "lost" and does not block while Excel is in edit mode.
Here's my additional C# code to try to make use of the Global Interface Table:
namespace ComServerTest
// Global Interface Table definition from pinvoke.net
ComImport,
InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
Guid("00000146-0000-0000-C000-000000000046")
interface IGlobalInterfaceTable
uint RegisterInterfaceInGlobal(
[MarshalAs(UnmanagedType.IUnknown)] object pUnk,
[In] ref Guid riid);
void RevokeInterfaceFromGlobal(uint dwCookie);
[return: MarshalAs(UnmanagedType.IUnknown)]
object GetInterfaceFromGlobal(uint dwCookie, [In] ref Guid riid);
ComImport,
Guid("00000323-0000-0000-C000-000000000046") // CLSID_StdGlobalInterfaceTable
class StdGlobalInterfaceTable /* : IGlobalInterfaceTable */
public class ManagerClass : IManagerClass
//...skipped code already mentioned in earlier sample above...
//...also skipped the message filter code for brevity...
private Guid IID_IDispatch = new Guid("00020400-0000-0000-C000-000000000046");
private IGlobalInterfaceTable m_GIT = null;
public ManagerClass()
//...skipped code already mentioned in earlier sample above...
m_GIT = (IGlobalInterfaceTable)new StdGlobalInterfaceTable();
public void FireEventOne()
// Using the GIT to marshal the (event?) interface from the main thread back to the main thread (like the MFC Automation server).
// Should we be marshalling the ManagerEvents interface pointer instead? How do we get at it?
uint uCookie = m_GIT.RegisterInterfaceInGlobal(this, ref IID_IDispatch);
ManagerClass mgr = (ManagerClass)m_GIT.GetInterfaceFromGlobal(uCookie, ref IID_IDispatch);
mgr.EventOne(); // when Excel is in edit mode, event handler is never called and does not block, event is "lost"
m_GIT.RevokeInterfaceFromGlobal(uCookie);
I’d like my C# COM server to behave in a similar way to the MFC Automation server.  Is this possible?  I think I should be registering the ManagerEvents interface pointer in the GIT but I don't know how to get at it? I tried using Marshal.GetComInterfaceForObject(this,
typeof(ManagerEvents)) but that just throws an exception: System.InvalidCastException: Specified cast is not valid.
Thanks.

Answer 1

Hi Jason-F,
I’ve found that when I raise COM events while Excel is in edit mode (e.g. a cell is being edited) the event is “lost”.  Meaning,
the VBA event handler is never called (even after the Excel edit mode is finished) and the call to the C# event delegate passes through and fails silently with no exceptions being thrown.
Do you mean you didn't raise EventOne event? EventOne handler like following?
' EventOne handler
Private Sub managerObj_EventOne()
Debug.Print "EventOne " & g_nCounter
g_nCounter = g_nCounter + 1
End Sub
After test your code, here is my screenshot
And here is my execute log in C# ComServerTest.
ManagerClass1/1/2015 5:48:11 PM
DoThreadWork()1/1/2015 5:48:12 PM
ManagerClass_EventOne()1/1/2015 5:48:17 PM
ManagerClass_EventOne()1/1/2015 5:48:22 PM
ManagerClass_EventOne()1/1/2015 5:48:27 PM
ManagerClass_EventOne()1/1/2015 5:48:32 PM
ManagerClass_EventOne()1/1/2015 5:48:37 PM
ManagerClass_EventOne()1/1/2015 5:48:42 PM
ManagerClass1/1/2015 5:49:56 PM
DoThreadWork()1/1/2015 5:49:56 PM
ManagerClass_EventOne()1/1/2015 5:50:01 PM
ManagerClass1/1/2015 5:50:04 PM
If i misunderstand you, please feel free to let me know.
Best regards,
kristin
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