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- QuickOPC-Classic in COM
- Reading, Writing, Subscriptions, Property Access
- Subscribing to a non-existent item
Subscribing to a non-existent item
08 Jul 2021 12:57 #9963
by lamar
Replied by lamar on topic Subscribing to a non-existent item
Sorry, I pasted the wrong "solution" . The working code is:I use 16 bit unsigned integer values, thefore 99999 is out of range. Works perfect.
However I did not understand why FlotToStrDef did not work...
If StrToIntDef(EventArgs.VTQ.Value,99999) <> 99999 Then ...However I did not understand why FlotToStrDef did not work...
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08 Jul 2021 12:55 #9962
by support
Replied by support on topic Subscribing to a non-existent item
I do not pretend to understand what is happening under the hoods, but I am glad that you have found a solution nevertheless.
Best regards
Best regards
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08 Jul 2021 12:47 #9961
by lamar
Replied by lamar on topic Subscribing to a non-existent item
There is the solution. So easy as it can be.
If StrToFloatDef(EventArgs.VTQ.Value, NaN) <> NaN Then ...Please Log in or Create an account to join the conversation.
08 Jul 2021 12:17 #9960
by lamar
Replied by lamar on topic Subscribing to a non-existent item
No, the main app that calls the DLL accepts only numerical values.
But as I wrote in my 08 Jul 2021 09:27 comment, I tried to avoid
empty string values inside the DLL without any success.
But as I wrote in my 08 Jul 2021 09:27 comment, I tried to avoid
empty string values inside the DLL without any success.
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08 Jul 2021 12:14 #9959
by support
Replied by support on topic Subscribing to a non-existent item
I am on to something.
What does not really work are the comparisons you have given as examplea:
It looks like that since the Value is OleVariant, the compiled code ends up calling methods like System.Variants.VarCompareSimple, and they throw an exception in case the variant types are not equal, and it halts the program. And the variant types are often not equal, because if you are dealing with generic&multiple OPC items, they will have different type, so comparing e.g. against a string will fail with a Double, comparing against a number will fail with a string, etc.
Anyway, this underlines the fact that in order to address this, if you do not find the cause yourself, I need to have a code for the repro, and not just "guess" how exactly your code looks like.
Best regards
What does not really work are the comparisons you have given as examplea:
I tried testing If EventArgs.VTQ.Value <> '' Then ...
I tried testing If EventArgs.VTQ.Value <> null Then ...
It looks like that since the Value is OleVariant, the compiled code ends up calling methods like System.Variants.VarCompareSimple, and they throw an exception in case the variant types are not equal, and it halts the program. And the variant types are often not equal, because if you are dealing with generic&multiple OPC items, they will have different type, so comparing e.g. against a string will fail with a Double, comparing against a number will fail with a string, etc.
Anyway, this underlines the fact that in order to address this, if you do not find the cause yourself, I need to have a code for the repro, and not just "guess" how exactly your code looks like.
Best regards
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08 Jul 2021 12:03 #9958
by support
Replied by support on topic Subscribing to a non-existent item
Is it possible that it has to do with the fact that a String has been returned for that item?
Have you tried any other String-typed item?
One from our server, OPCLabs.KitServer.2 : Simulation.Register_BSTR
One from Matrikon server, Matrikon.OPC.Simulation.1 : Random.String
Regards
Have you tried any other String-typed item?
One from our server, OPCLabs.KitServer.2 : Simulation.Register_BSTR
One from Matrikon server, Matrikon.OPC.Simulation.1 : Random.String
Regards
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08 Jul 2021 11:55 #9957
by lamar
Replied by lamar on topic Subscribing to a non-existent item
Absolutely right.
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08 Jul 2021 11:51 #9956
by support
Replied by support on topic Subscribing to a non-existent item
Please clarify: "...any kind of touching EventArgs.VTQ.Value will cause freezing".
The above only applies to certain "problematic" item(s), such as 'Bucket Brigade.UIntqa', right? In other cases, you can access EventArgs.VTQ.Value without an issue?
Regards
The above only applies to certain "problematic" item(s), such as 'Bucket Brigade.UIntqa', right? In other cases, you can access EventArgs.VTQ.Value without an issue?
Regards
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08 Jul 2021 10:32 #9955
by lamar
Replied by lamar on topic Subscribing to a non-existent item
I got the same result.
However, in the DLL, any kind of touching EventArgs.VTQ.Value will cause freezing.
Do you have any ideas for preventing this?
Are there any other flags to check?
Or maybe checking the event timestamp?
However, in the DLL, any kind of touching EventArgs.VTQ.Value will cause freezing.
Do you have any ideas for preventing this?
Are there any other flags to check?
Or maybe checking the event timestamp?
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08 Jul 2021 10:03 #9954
by support
Replied by support on topic Subscribing to a non-existent item
Ok I see, I misunderstood the purpose of the last test app.
Regarding the freezing: I changed both my test example, and this app of yours, to access and use the EventArgs.VTQ.Value for 'Bucket Brigade.UIntqa', and it works OK in both cases.
The updated code in my example looks like this:
The updated code in your example looks like this:
Regards
Regarding the freezing: I changed both my test example, and this app of yours, to access and use the EventArgs.VTQ.Value for 'Bucket Brigade.UIntqa', and it works OK in both cases.
The updated code in my example looks like this:
// Handle the notification event
if eventArgs.Succeeded then
begin
WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq.ToString);
if (eventArgs.Vtq.HasValue) then
WriteLn(' <', eventArgs.Vtq.Value, '>');
end
else
WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief);The updated code in your example looks like this:
Edit3.text := 'Edit3 text changed unexpectedly <' + EventArgs.VTQ.Value + '>';Regards
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