IMessageFilter::HandleInComingCall method (objidl.h)

Provides a single entry point for incoming calls.

This method is called prior to each method invocation originating outside the current process and provides the ability to filter or reject incoming calls (or callbacks) to an object or a process.


DWORD HandleInComingCall(
  [in] DWORD           dwCallType,
  [in] HTASK           htaskCaller,
  [in] DWORD           dwTickCount,
  [in] LPINTERFACEINFO lpInterfaceInfo


[in] dwCallType

The type of incoming call that has been received. Possible values are from the enumeration CALLTYPE.

[in] htaskCaller

The thread id of the caller.

[in] dwTickCount

The elapsed tick count since the outgoing call was made, if dwCallType is not CALLTYPE_TOPLEVEL. If dwCallType is CALLTYPE_TOPLEVEL, dwTickCount should be ignored.

[in] lpInterfaceInfo

A pointer to an INTERFACEINFO structure that identifies the object, interface, and method being called. In the case of DDE calls, lpInterfaceInfo can be NULL because the DDE layer does not return interface information.

Return value

This method can return the following values.

Return code Description
The application might be able to process the call.
The application cannot handle the call due to an unforeseen problem, such as network unavailability, or if it is in the process of terminating.
The application cannot handle the call at this time. An application might return this value when it is in a user-controlled modal state.


If implemented, HandleInComingCall is called by COM when an incoming COM message is received.

Depending on an application's current state, a call is either accepted and processed or rejected (permanently or temporarily). If SERVERCALL_ISHANDLED is returned, the application may be able to process the call, although success depends on the interface for which the call is destined. If the call cannot be processed, COM returns RPC_E_CALL_REJECTED.

Input-synchronized and asynchronous calls are dispatched even if the application returns SERVERCALL_REJECTED or SERVERCALL_RETRYLATER.

HandleInComingCall should not be used to hold off updates to objects during operations such as band printing. For that purpose, use IViewObject::Freeze.

You can also use HandleInComingCall to set up the application's state so that the call can be processed in the future.

Note  Although the htaskCaller parameter is typed as an HTASK, it contains the thread id of the calling thread. When you implement the IMessageFilter interface, you can call the OpenThread function to get the thread handle from the htaskCaller parameter, and you can call the GetProcessIdOfThread function to get the process id.


Requirement Value
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header objidl.h

See also