dOPC Client Toolkit Help file
TdOPCEvent.ChangeMask Property
C++
__published: __property int ChangeMask;
C#
int ChangeMask;
Visual Basic
Property ChangeMask() As Integer

ChangeMask indicates what properties of the condition have changed and forced the server to send the event notification.

Value 
Description 
opc_Change_Active_State 
the condition's active state has changed 
opc_Change_Ack_State 
the condition's acknowledgment state has changed 
opc_Change_Enable_State 
the condition's enabled state has changed 
opc_Change_Quality 
the condition's quality has changed 
opc_Change_Severity 
the severity level has changed 
opc_Change_Subcondition 
the condition has transitioned into a new sub-condition 
opc_Change_Message 
the event message has changed (compared to prior event notifications related to this condition) 
opc_Change_Attribute 
one or more event attributes have changed (compared to prior event notifications related to this condition) 

If the event notification is the result of a refresh, these bits have to be ignored. For a "new event", opc_Change_Active_State is the only bit which will always be set. Other values are server-specific. (A "new event" is any event resulting from the related condition leaving the Inactive and Acknowledged state.)

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