AsyncRead method
Description | Read one or more items in a group. The results are returned via the AsyncReadComplete event associated with the OPCGroup object |
Syntax | AsyncRead ( NumItems As Long, ServerHandles() As Long, ByRef Errors() As Long, TransactionID As Long, ByRef CancelID As Long)NumItems — Number of items to be read.ServerHandles — Array containing server handles for the items to be read.Errors — Variant containing an Integer array of errors returned to the client indicating the success/failure of the individual items to be read.TransactionID — The client specified transaction ID. This is included in the 'completion' information provided in the AsyncReadComplete Event.CancelID — A Server generated CancelID. This is provided to enable the client to cancel the Transaction. |
Remarks | The AsyncRead requires the OPCGroup object to have been dimensioned to handle events (Dim WithEvents MyOPCGroup As OPCGroup) in order for the results of the AsyncRead operation to be returned to the client. The AsyncReadComplete event associated with the OPCGroup object will be called by the Data Access Server with the results of the AsyncRead operation. |
Example | Dim lNumitems As Long Dim arHandles() As Long Dim arErrors() As Long Dim lTransID As Long Dim lCancelID As Long Dim MyOPCItem As OPCItem '/* Specify number of elements lNumitems = MyOPCGroup.OPCItems.Count ReDim arHandles(1 To lNumitems) For i = 1 To lNumitems 'pass in server handles arHandles(i) = MyOPCGroup.OPCItems(i).ServerHandle Next 'i MyOPCGroup.AsyncRead lNumitems, arHandles, arErrors, lTransID, lCancelID '/* Check for errors For i = 1 To lNumitems If arErrors(i) > 0 Then txtStatus = MyOPCServer.GetErrorString(arErrors(i)) End If Next 'i |
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