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OPCDA subscription Cast Error in Delphi

wsalvin
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15 Sep 2025 13:48 #14369 by wsalvin

Replied by wsalvin on topic OPCDA subscription Cast Error in Delphi

Okay,
Thank you for your help.
I find the Issue, the TLBs were not overrided.
Now it works, I will check if i still face memory leak.
And i will open another tread in case.
Regards

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support
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15 Sep 2025 09:52 #14368 by support

Replied by support on topic OPCDA subscription Cast Error in Delphi

The I in angle brackets means "switch to italics" - this is BBCode, quite common in forums - en.wikipedia.org/wiki/BBCode .

Enclose the entirety of your code in [code] instead.

I will rethink my answer and reply later.

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wsalvin
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15 Sep 2025 09:50 #14367 by wsalvin

Replied by wsalvin on topic OPCDA subscription Cast Error in Delphi

Hello,
I suspect the TLBs was not overrided. let me do it again. I keep you informed.
Thank

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wsalvin
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15 Sep 2025 09:24 #14366 by wsalvin

Replied by wsalvin on topic OPCDA subscription Cast Error in Delphi

again the "I" disappear. see previous screen shot.

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15 Sep 2025 09:22 #14365 by wsalvin

Replied by wsalvin on topic OPCDA subscription Cast Error in Delphi

Oups sorry.
I just checked my code.see screen shot.
in my code it's Arguments := ItemSubscriptionArguments;

I do not know why when i copy past the code the '' disappear.
regards

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15 Sep 2025 09:05 - 15 Sep 2025 09:05 #14364 by support

Replied by support on topic OPCDA subscription Cast Error in Delphi

In your code, you create the Arguments as an array, that's true. But then, inside the loop, you overwrite with just one element:

Arguments := ItemSubscriptionArguments;

I do not see how this can work.

Regards

Last edit: 15 Sep 2025 09:05 by support.

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wsalvin
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15 Sep 2025 08:56 #14363 by wsalvin

Replied by wsalvin on topic OPCDA subscription Cast Error in Delphi

Hello,
My code is based on your exemple. the only diff is only that the number of requested Tag is a parameter and is include in a VCL app.
I create an Array : Arguments := VarArrayCreate([0, NbTag - 1], varVariant); to pass to SubscribeMultipleItems.
My code was working well on \OPC Labs QuickOPC 2020.2 except a memory leak.
So I upgrade on 2025 in order to see if the memory leak is fixed. but i no more able to run my appli an i face the issue i sent you as screen shot on previous mail.
To upgrade i installed the new 2025 release a regenerate TLB from SDK/Lib folder.
When I run the application I checked the DLL loaded by my app and now its the 2025 one.
Any idea of what else i can do?
Regards

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15 Sep 2025 08:29 #14362 by support

Replied by support on topic OPCDA subscription Cast Error in Delphi

Hello._EasyDAItemSubscriptionArguments is the right type for SubscribeMultipleItems. However, it has to be an *array* of them. Why don't you just base your code on the example provided for SubscribeMultipleItems? From opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Late...e%20to%20multiple%20items.html :

Code:

// This example shows how to subscribe to changes of multiple items and display the value of the item with each change.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in Object Pascal (Delphi) on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-OP .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

type
  TSubscribeMultipleItems_ClientEventHandlers = class
    // Item changed event handler
    procedure OnItemChanged(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyDAItemChangedEventArgs);
  end;

procedure TSubscribeMultipleItems_ClientEventHandlers.OnItemChanged(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyDAItemChangedEventArgs);
begin
  if eventArgs.Succeeded then
    WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq.ToString)
  else
    WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief);
end;

class procedure SubscribeMultipleItems.Main;
var
  Arguments: OleVariant;
  Client: TEasyDAClient;
  ClientEventHandlers: TSubscribeMultipleItems_ClientEventHandlers;
  HandleArray: OleVariant;
  ItemSubscriptionArguments1: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments2: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments3: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments4: _EasyDAItemSubscriptionArguments;
begin
  ItemSubscriptionArguments1 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments1.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments1.ItemDescriptor.ItemID := 'Simulation.Random';
  ItemSubscriptionArguments1.GroupParameters.RequestedUpdateRate := 1000;

  ItemSubscriptionArguments2 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments2.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments2.ItemDescriptor.ItemID := 'Trends.Ramp (1 min)';
  ItemSubscriptionArguments2.GroupParameters.RequestedUpdateRate := 1000;

  ItemSubscriptionArguments3 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments3.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments3.ItemDescriptor.ItemID := 'Trends.Sine (1 min)';
  ItemSubscriptionArguments3.GroupParameters.RequestedUpdateRate := 1000;

  ItemSubscriptionArguments4 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments4.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments4.ItemDescriptor.ItemID := 'Simulation.Register_I4';
  ItemSubscriptionArguments4.GroupParameters.RequestedUpdateRate := 1000;

  Arguments := VarArrayCreate([0, 3], varVariant);
  Arguments[0] := ItemSubscriptionArguments1;
  Arguments[1] := ItemSubscriptionArguments2;
  Arguments[2] := ItemSubscriptionArguments3;
  Arguments[3] := ItemSubscriptionArguments4;

  // Instantiate the client object and hook events
  Client := TEasyDAClient.Create(nil);
  ClientEventHandlers := TSubscribeMultipleItems_ClientEventHandlers.Create;
  Client.OnItemChanged := ClientEventHandlers.OnItemChanged;

  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(
    Client.SubscribeMultipleItems(Arguments));

  WriteLn('Processing item changed events for 1 minute...');
  PumpSleep(60*1000);

  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllItems;

  WriteLn('Waiting for 5 seconds...');
  PumpSleep(5*1000);

  WriteLn('Finished.');
  VarClear(HandleArray);
  VarClear(Arguments);
  FreeAndNil(Client);
  FreeAndNil(ClientEventHandlers);
end;

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wsalvin
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15 Sep 2025 07:43 #14361 by wsalvin

OPCDA subscription Cast Error in Delphi was created by wsalvin

hello i'm doing the following test In Delphi 12 with the last release QuickOPC (2025.1) I just downloaded.

procedure TForm3.btnAddOpcdaClick(Sender: TObject);
var
Arguments: OleVariant;
ItemSubscriptionArguments: _EasyDAItemSubscriptionArguments;
// ItemSubscriptionArguments: _DAReadItemArguments;
// ItemSubscriptionArguments: _DAItemGroupArguments;
HandleArray: OleVariant;
I: Integer;
begin
// exemple in kb.opclabs.com/Reference_counting_in_Delphi
//https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/User%27s%20Guide%20and%20Reference-OPC%20Studio/Examples%20-%20OPC%20Data%20Access%20-%20Subscribe%20to%20multiple%20items.html
// CoInitialize(nil);
ClientEventHandlers := TClientEventHandlers.Create;
ClientOPCDA := TEasyDAClient.Create(nil);
ClientOPCDA.OnItemChanged := ClientEventHandlers.OnDataChangeNotification;
Arguments := VarArrayCreate([0, NbTag - 1], varVariant);

//init tag requested
for I := 0 to NbTag - 1 do
begin
ItemSubscriptionArguments := CoEasyDAItemSubscriptionArguments.Create;
// ItemSubscriptionArguments := CoDAReadItemArguments.Create;
// ItemSubscriptionArguments := CoDAItemGroupArguments.Create;
//Nom du PC
ItemSubscriptionArguments.ServerDescriptor.MachineName := 'localhost';
//Nom du serveur OPC
ItemSubscriptionArguments.ServerDescriptor.ServerClass := 'Kepware.KEPServerEX.V6';
//Nom du tag OPC
ItemSubscriptionArguments.ItemDescriptor.ItemID := 'Simulation Examples.Functions.Ramp' + (I + 1).ToString;
//Delai de rafraichissement
ItemSubscriptionArguments.GroupParameters.RequestedUpdateRate := 1000;
Arguments := ItemSubscriptionArguments;
end;
ClientOPCDA.SubscribeMultipleItems(Arguments);

btnAddOpcda.Enabled := False;
btnRemOpcda.Enabled := True;
CodeSite.send('OPCDA Added');
end;

I face the following Error.
Impossible d'effectuer un cast d'un objet de type 'OpcLabs.EasyOPC.DataAccess.OperationModel.EasyDAItemSubscriptionArguments en type OpcLabs.EasyOPC.DataAccess.OperationModel.DaReadItemArguments.

Is _EasyDAItemSubscriptionArguments the right type to use for the array to pass to SubscribeMultipleItems?
Regards

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