virtual HRESULT STDMETHODCALLTYPE OnEvent( /* [in] */ OPCHANDLE hClientSubscription, /* [in] */ BOOL bRefresh, /* [in] */ BOOL bLastRefresh, /* [in] */ DWORD dwCount, /* [size_is][in] */ ONEVENTSTRUCT *pEvents) = 0;.

typedef /* [public][public] */ struct __MIDL___MIDL_itf_opc_ae_0262_0004 { WORD wChangeMask; WORD wNewState; /* [string] */ LPWSTR szSource; FILETIME ftTime; /* [string] */ LPWSTR szMessage; DWORD dwEventType; DWORD dwEventCategory; DWORD dwSeverity; /* [string] */ LPWSTR szConditionName; /* [string] */ LPWSTR szSubconditionName; WORD wQuality; WORD wReserved; BOOL bAckRequired; FILETIME ftActiveTime; DWORD dwCookie; DWORD dwNumEventAttrs; /* [size_is] */ VARIANT *pEventAttributes; /* [string] */ LPWSTR szActorID; } ONEVENTSTRUCT;.