Opc data Access Automation Specification

4.3.6

 

OPCGroups Events 

4.3.6.1

 

GlobalDataChange 

Description 

The GlobalDataChangeevent is an event to facilitate one event handler being implemented to 

receive and process data changes across multiple groups. 

Syntax 

GlobalDataChange (TransactionID As Long, GroupHandle As Long, NumItems As Long, 

ClientHandles() As Long, ItemValues() As Variant, Qualities() As Long, TimeStamps() As Date) 

 

Part Description 

TransactionID 

The client specified transaction ID.  A non-0 value for this indicates 

that this call has been generated as a result of an AsyncRefresh.  A 

value of 0 indicates that this call has been generated as a result of 

normal subscription processing. 

GroupHandle 

ClientHandle of the OPCGroup Object the changed data corresponds 

to. 

NumItems 

The number of items returned 

ClientHandles 

Array of client item handles for the items  

ItemValues 

Array of values. 

Qualities 

Array of Qualities for each item's value. 

TimeStamps 

Array of UTC TimeStamps for each item's value 

 

Remarks 

NOTE – it is recommended that the event OnDataChange on the OPCGroup object be used normally. 

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OPC Data Access Automation Specification2.02 

This event has been provided to facilitate one event handler being set up to process data changes for 

multiple OPCGroup objects.  Normally, your application has an individual event handler for each 

group to receive and process the data changes. This allows you to have one event handler, and then 

using the GroupHandle, know  which Group the event has been fired on behalf of. 

This event will be invoked for each OPCGroup object that contains an item, whose value or state of 

the value has changed since the last time this event, was fired.   The individual event on the 

OPCGroup object is also fired as well.  Your application, when using both event handlers will receive 

the data value twice, once for the individual group event, and once for the AllGroupsDataChange 

Event. 

Example 

Dim WithEvents AnOPCGroupCollection As OPCGroups 

Private Sub AnOPCGroupCollection_GlobalDataChange (TransactionID As Long, GroupHandle As 

Long, MasterQuality As Long, MasterError As Long, NumItems As Long, ClientHandles() As 

Long, ItemValues() As Variant, Qualities() As Long, TimeStamps() As Date) 

‘ write your client code here to process the data change values  

End Sub 

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OPC Data Access Automation Specification2.02