How do I implement AsyncRead in C#?|OPC UA Standard|Forum|OPC Foundation

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How do I implement AsyncRead in C#?
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Denis Pozarko
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05/19/2021 - 00:30
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I can’t find exact solution on github samples. Can you please provide the link to it?

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Randy Armstrong
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05/19/2021 - 02:21
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What are you calling AsyncRead?

UA does not support the AsyncRead features of COM.

Any AsyncRead is implemented using client side features of the programming language.

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Denis Pozarko
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05/19/2021 - 04:22
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Oh I accidently posted in wrong subforum. It is in DA.

This is what I’ve tried so far, I keep getting “Value does not fall withing expected range”. Why is that?

public void AsyncReadStart(string groupName, ListView formListView) { newListView = formListView; asyncGroupNames.Add(groupName); int numItems = structOPCServers[selectedNodeindex].opcServer.OPCGroups.GetOPCGroup(groupName).OPCItems.Count+1; structOPCServers[selectedNodeindex].a_serverHandles = new int[numItems]; int i = 1; foreach(OPCItem item in structOPCServers[selectedNodeindex].opcGroup.OPCItems) { structOPCServers[selectedNodeindex].a_serverHandles.SetValue(item.ServerHandle, i); i++; } int transID = 1231; //int NumItems, ref Array ServerHandles, out Array Errors, int TransactionID, out int cancelIDs structOPCServers[selectedNodeindex].opcServer.OPCGroups.GetOPCGroup(groupName).AsyncRead(numItems, ref structOPCServers[selectedNodeindex].a_serverHandles, out structOPCServers[selectedNodeindex].a_errors, transID, out int cancelID); //Exception appears in line above. structOPCServers[selectedNodeindex].opcServer.OPCGroups.GetOPCGroup(groupName).AsyncReadComplete += OPC_Logic_AsyncReadComplete; }
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Randy Armstrong
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05/19/2021 - 05:41
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VB is fussy about Variants vs simple types.

You likely need a cast.

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Denis Pozarko
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05/20/2021 - 00:26
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Can you please provide me with example code, I’ve tried to cast it to different types and much more none seem to work.

This is metadata from IOPCGroup:

void AsyncRead(int NumItems, ref Array ServerHandles, out Array Errors, int TransactionID, out int CancelID);

 

AsyncRead(numItems, ref structOPCServers[selectedNodeindex].a_serverHandles, out structOPCServers[selectedNodeindex].a_errors, transID, out cancelID);

In my code:

numItems is int

structOPCServers[selectedNodeindex].a_serverHandles is Array

structOPCServers[selectedNodeindex].a_errors is Array

transID is int

cancelID is int

I really have no idea what to do.

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Randy Armstrong
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05/20/2021 - 06:21
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There is no C# sample code that uses the VB automation wrapper that I am aware of.

You may have more success of you use VB.

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