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06/29/2023
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Hello, could you help me to understand the Refresh() process when there were not any active nor unacknowledged condition on AE server?
Should the AE server send an empty list of EventNotifications with Refresh and LastRefresh flags true?
I get some mixed result with a customer's server. The server sometimes send nothing, and sometimes send empty pEvents to OpcCom.Ae.Subscription.OnEvent(
int hClientSubscription,
int bRefresh,
int bLastRefresh,
int dwCount,
OpcRcw.Ae.ONEVENTSTRUCT[] pEvents)
which will cause exception:
System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=OpcNetApi.Com
StackTrace:
at OpcCom.Ae.Subscription.Callback.OnEvent(Int32 hClientSubscription, Int32 bRefresh, Int32 bLastRefresh, Int32 dwCount, ONEVENTSTRUCT[] pEvents) in xxxxxxxxxx\NetCore\OpcNetApi.Com\Ae\OpcCom.Ae.Subscription.cs:line 523
This exception was originally thrown at this call stack:
OpcCom.Ae.Subscription.Callback.OnEvent(int, int, int, int, OpcRcw.Ae.ONEVENTSTRUCT[]) in OpcCom.Ae.Subscription.cs
05/30/2017
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Do you have the code for the NET API?
06/29/2023
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Yes, as member of OPC Foundation, I do have the access to the NET API source code. Is OPC AE server expected always reply on Refresh() even if there were not any active nor unacked conditions? What would recommend? I am not sure am I allowed to put any source code here though.
05/30/2017
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The issue is the null pointer exception should not occur. The code should check dwCount and if zero it should not access pEvents.
If you fix the null pointer exception in your copy of the code we can see if the issue goes away.
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