Opc data Access Automation Specification

4.4.5.5

 

AsyncRefresh 

Description 

Generate an event for all active items in the group (whether they have changed or not).  Inactive 

items are not included in the callback. The results are returned via the DataChange event 

associated with the OPCGroup object, as well as the GlobalDataChange event associated with the 

OPCGroups object. 

Syntax 

AsyncRefresh(Source As Integer, TransactionID As Long,ByRef CancelID As Long) 

 

Part Description 

Source 

The ‘data source’; OPC_DS_CACHE or OPC_DS_DEVICE  

TransactionID 

The client specified transaction ID. This is included in the 

‘completion’ information provided in the Corresponding Event. 

CancelID 

A Server generated transaction ID. This is provided to enable the 

client to cancel the “transaction”. 

 

Remarks 

The AsyncRefresh requires the OPCGroup object to have been dimensioned with events (Dim 

WithEvents xxx As OPCGroup) in order for the results of the refresh operation to be returned to the 

automation client application.  The DataChange event associated with the OPCGroup object will be 

fired (called) by the automation server with the results of the refresh operation.  

If the automation cleint application has dimensioned with events the OPCGroups Object (Dim 

WithEvents xyz as OPCGroups), then the GlobalDataChange event associated with the OPCGroups  

object will be fired (called) by the automation server with the results of the refresh operation. 

See Also 

IOPCAsyncIO::Refresh from the OPC Data Access Custom Interface Specification. 

Example 

Dim MyGroups As OPCGroups 

Dim DefaultGroupUpdateRate As Long 

Dim WithEvents OneGroup As OPCGroup 

Private Sub AsyncRefreshButton_Click() 

Dim ServerIndex As Long  

Dim Source As Long 

Dim ClientTransactionID As Long  

Dim ServerTransactionID As Long 

ClientTransactionID = 2125 

Source = OPC_DS_DEVICE 

OneGroup.AsyncRefresh Source, ClientTransactionID ServerTransactionID 

End Sub 

58 

 

---

OPC Data Access Automation Specification2.02