Opc data Access Automation Specification

4.4.5.6

 

AsyncCancel 

Description 

Request that the server cancel an outstanding transaction. An AsyncCancelComplete event will 

occur indicating whether or not the cancel succeeded. 

Syntax AsyncCancel(CancelID 

As 

Long) 

Part Description 

CancelID 

The Server generated CancelID that was previously returned by the 

AsyncRead, AsyncWrite or AsyncRefresh method that the client now 

wants to cancel.  

See Also 

IOPCAsyncIO2::Cancel from the OPC Data Access Custom Interface Specification 

Remarks 

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

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

to the automation client application.  The AsyncCancelComplete event associated with the 

OPCGroup object will be fired (called) by the automation server with the results of the AsyncCancel 

operation. The client specified transaction ID (TransactionID) will be returned to the automation 

client application in the AsyncCancelComplete event. 

Example Private 

Sub 

AsyncCancelButton_Click() 

Dim ServerIndex As Long  

Dim CancelID As Long 

CancelID = 1 ‘ some transaction id returned from one of the async calls like read, write, or refresh. 

OneGroup.AsyncCancel CancelID 

End Sub