OPC Studio User's Guide and Reference
Examples - OPC Data Access - Event pull

Example with single item:

.NET

// This example shows how to subscribe to item changes and obtain the events by pulling them.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class PullItemChanged
    {
        public static void Main1()
        {
            // Instantiate the client object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyDAClient { PullItemChangedQueueCapacity = 1000 };

            Console.WriteLine("Subscribing item changes...");
            client.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

            Console.WriteLine("Processing item changes for 1 minute...");
            int endTick = Environment.TickCount + 60 * 1000;
            do
            {
                EasyDAItemChangedEventArgs eventArgs = client.PullItemChanged(2 * 1000);
                if (!(eventArgs is null))
                    // Handle the notification event
                    Console.WriteLine(eventArgs);
            } while (Environment.TickCount < endTick);

            Console.WriteLine("Unsubscribing item changes...");
            client.UnsubscribeAllItems();

            Console.WriteLine("Finished.");
        }
    }
}

# This example shows how to subscribe to item changes and obtain the events by pulling them.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.DataAccess

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"

# Instantiate the client object.
$client = New-Object EasyDAClient
# In order to use event pull, you must set a non-zero queue capacity upfront.
$client.PullItemChangedQueueCapacity = 1000

Write-Host "Subscribing item..."
[IEasyDAClientExtension]::SubscribeItem($client, "", "OPCLabs.KitServer.2", "Simulation.Random", 1000)

Write-Host "Processing item changes for 1 minute..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 60) {    
    $eventArgs = [IEasyDAClientExtension]::PullItemChanged($client, 2*1000)
    if ($eventArgs -ne $null) {
        # Handle the notification event
        Write-Host $eventArgs
    }
}

Write-Host "Unsubscribing items..."
$client.UnsubscribeAllItems()

Write-Host "Finished."

# This example shows how to subscribe to item changes and obtain the events by pulling them.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.DataAccess import *


# Instantiate the client object
client = EasyDAClient()
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')
IEasyDAClientExtension.SubscribeItem(client, '', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000)

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = IEasyDAClientExtension.PullItemChanged(client, 2*1000)
    if eventArgs is not None:
        # Handle the notification event
        print(eventArgs)

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

' This example shows how to subscribe to item changes and obtain the events by pulling them.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class PullItemChanged
        Public Shared Sub Main1()
            Dim client = New EasyDAClient()
            ' In order to use event pull, you must set a non-zero queue capacity upfront.
            client.PullItemChangedQueueCapacity = 1000

            Console.WriteLine("Subscribing item changes...")
            client.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000)

            Console.WriteLine("Processing item changes for 1 minute...")
            Dim endTick As Integer = Environment.TickCount + 60 * 1000
            Do
                Dim eventArgs As EasyDAItemChangedEventArgs = client.PullItemChanged(2 * 1000)
                If Not eventArgs Is Nothing Then
                    ' Handle the notification event
                    Console.WriteLine(eventArgs)
                End If
            Loop While Environment.TickCount < endTick

            Console.WriteLine("Unsubscribing item changes...")
            client.UnsubscribeAllItems()

            Console.WriteLine("Finished.")
        End Sub
    End Class
End Namespace

COM

// This example shows how to subscribe to item changes and obtain the events by pulling them.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

var Client = new ActiveXObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
// In order to use event pull, you must set a non-zero queue capacity upfront.
Client.PullItemChangedQueueCapacity = 1000;

WScript.Echo("Subscribing item changes...");
Client.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

WScript.Echo("Processing item changes for 1 minute...");
var endTime = new Date().getTime() + 60*1000
do {
    var EventArgs = Client.PullItemChanged(2*1000);
    if (EventArgs !== null) {
        //  Handle the notification event
        WScript.Echo(EventArgs);
    }
} while(new Date().getTime() < endTime);

WScript.Echo("Unsubscribing item changes...");
Client.UnsubscribeAllItems();

WScript.Echo("Finished.");

// This example shows how to subscribe to item changes and obtain the events by pulling them.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure PullItemChanged.Main;
var
  Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
  EndTick: Cardinal;
  EventArgs: _EasyDAItemChangedEventArgs;
begin
  // Instantiate the client object
  Client := CoEasyDAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullItemChangedQueueCapacity := 1000;

  WriteLn('Subscribing item changes...');
  Client.SubscribeItem('', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000);

  WriteLn('Processing item changes for 1 minute...');
  EndTick := Ticks + 60*1000;
  while Ticks < EndTick do
  begin
    EventArgs := Client.PullItemChanged(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      WriteLn(EventArgs.ToString);
  end;

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

  WriteLn('Finished.');
end;

// This example shows how to subscribe to item changes and obtain the events by pulling them.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
// In order to use event pull, you must set a non-zero queue capacity upfront.
$Client->PullItemChangedQueueCapacity = 1000;

print "Subscribing item changes...\n";
$Client->SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

print "Processing item changed events for 1 minute...\n";
$endTime = time() + 60;
do {
    $EventArgs = $Client->PullItemChanged(2*1000);
    if (!is_null($EventArgs)) {
        // Handle the notification event
        print $EventArgs->ToString();
        print "\n";
    }
} while (time() < $endTime);

// This example shows how to subscribe to item changes and obtain the events by pulling them.

mle_outputtext.Text = ""

// Instantiate the client object
OLEObject client
client = CREATE OLEObject
client.ConnectToNewObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
// In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

mle_outputtext.Text = mle_outputtext.Text + "Subscribing item changes..." + "~r~n"
client.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000)

mle_outputtext.Text = mle_outputtext.Text + "Processing item changes for 1 minute..." + "~r~n"

Time endTime = RelativeTime(Now(), 60)
DO
    OLEObject eventArgs
    eventArgs = client.PullItemChanged(2*1000)
    IF NOT IsNull(eventArgs) THEN
        // Handle the notification event
        mle_outputtext.Text = mle_outputtext.Text + eventArgs.DisplayString + "~r~n"
    END IF
LOOP WHILE Now() < endTime

mle_outputtext.Text = mle_outputtext.Text + "Unsubscribing item changes..." + "~r~n"
client.UnsubscribeAllItems()

mle_outputtext.Text = mle_outputtext.Text + "~r~n" 
mle_outputtext.Text = mle_outputtext.Text + "Finished." + "~r~n" 

# This example shows how to subscribe to item changes and obtain the events by pulling them.
#
# The Python for Windows (pywin32) extensions package is needed. Install it using "pip install pypiwin32".
# CAUTION: We now recommend using Python.NET package instead. Full set of examples with Python.NET is available!
#
# Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
import time
import win32com.client

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient') 
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')
client.SubscribeItem('', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000)

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = client.PullItemChanged(2*1000)
    if eventArgs is not None:
        # Handle the notification event
        print(eventArgs)

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

REM This example shows how to subscribe to item changes and obtain the events by pulling them.
REM
REM Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Private Sub PullItemChanged_Main_Command_Click()
    OutputText = ""
    
    Dim eventArgs As EasyDAItemChangedEventArgs
    
    ' Instantiate the client object
    Dim client As New EasyDAClient
    
    ' In order to use event pull, you must set a non-zero queue capacity upfront.
    client.PullItemChangedQueueCapacity = 1000
    
    OutputText = OutputText & "Subscribing item changes..." & vbCrLf
    Call client.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000)
    
    OutputText = OutputText & "Processing item changes for 1 minute..." & vbCrLf
    Dim endTick As Long
    endTick = GetTickCount + 60000
    While GetTickCount < endTick
        Set eventArgs = client.PullItemChanged(2 * 1000)
        If Not eventArgs Is Nothing Then
            ' Handle the notification event
            OutputText = OutputText & eventArgs & vbCrLf
        End If
    Wend
    
    OutputText = OutputText & "Unsubscribing item changes..." & vbCrLf
    client.UnsubscribeAllItems

    OutputText = OutputText & "Finished." & vbCrLf
End Sub

Rem This example shows how to subscribe to item changes and obtain the events by pulling them.
Rem
Rem Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Option Explicit

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
' In order to use event pull, you must set a non-zero queue capacity upfront.
Client.PullItemChangedQueueCapacity = 1000

WScript.Echo "Subscribing item changes..."
Client.SubscribeItem "", "OPCLabs.KitServer.2", "Simulation.Random", 1000

WScript.Echo "Processing item changes for 1 minute..."
Dim endTime: endTime = Now() + 60*(1/24/60/60)
Do
    Dim EventArgs: Set EventArgs = Client.PullItemChanged(2*1000)
    If Not (EventArgs Is Nothing) Then
        ' Handle the notification event
        WScript.Echo EventArgs
    End If    
Loop While Now() < endTime

WScript.Echo "Unsubscribing item changes..."
Client.UnsubscribeAllItems

WScript.Echo "Finished."

Example with multiple items:

.NET

// This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class PullItemChanged
    {
        public static void MultipleItems()
        {
            // Instantiate the client object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyDAClient { PullItemChangedQueueCapacity = 1000 };

            Console.WriteLine("Subscribing item changes...");
            client.SubscribeMultipleItems(
                new[] {
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, null),
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000, null),
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, null),
                    // Intentionally specifying an unknown item here, to demonstrate its behavior.
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "SomeUnknownItem", 1000, null)
                });

            Console.WriteLine("Processing item changes for 1 minute...");
            int endTick = Environment.TickCount + 60 * 1000;
            do
            {
                EasyDAItemChangedEventArgs eventArgs = client.PullItemChanged(2 * 1000);
                if (!(eventArgs is null))
                    // Handle the notification event
                    if (eventArgs.Succeeded)
                        Console.WriteLine($"{eventArgs.Arguments.ItemDescriptor.ItemId}: {eventArgs.Vtq}");
                    else
                        Console.WriteLine($"{eventArgs.Arguments.ItemDescriptor.ItemId} *** Failure: {eventArgs.ErrorMessageBrief}");
            } while (Environment.TickCount < endTick);

            Console.WriteLine("Unsubscribing item changes...");
            client.UnsubscribeAllItems();

            Console.WriteLine("Finished.");
        }
    }
}

# This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.DataAccess
using namespace OpcLabs.EasyOpc.DataAccess.OperationModel

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"

# Instantiate the client object.
$client = New-Object EasyDAClient
# In order to use event pull, you must set a non-zero queue capacity upfront.
$client.PullItemChangedQueueCapacity = 1000

Write-Host "Subscribing item changes..."
$handleArray = [OpcLabs.EasyOpc.DataAccess.IEasyDAClientExtension]::SubscribeMultipleItems($client, @(
    (New-Object DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, $null)),
    (New-Object DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000, $null)),
    (New-Object DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, $null)),
    # Intentionally specifying an unknown item here, to demonstrate its behavior.
    (New-Object DAItemGroupArguments("", "OPCLabs.KitServer.2", "SomeUnknownItem", 1000, $null))
    ))

Write-Host "Processing item changes for 1 minute..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 60) {    
    $eventArgs = [IEasyDAClientExtension]::PullItemChanged($client, 2*1000)
    if ($eventArgs -ne $null) {
        # Handle the notification event
        if ($eventArgs.Succeeded) {
            Write-Host "$($eventArgs.Arguments.ItemDescriptor.ItemId): $($eventArgs.Vtq)"
        }
        else {
            Write-Host "$($eventArgs.Arguments.ItemDescriptor.ItemId) *** Failure: $($eventArgs.ErrorMessageBrief)"
        }
    }
}

Write-Host "Unsubscribing item changes..."
$client.UnsubscribeAllItems()

Write-Host "Finished."

# This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *


# Instantiate the client object
client = EasyDAClient()
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')
client.SubscribeMultipleItems([
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Trends.Ramp (1 min)', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Trends.Sine (1 min)', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'UnknownItem', 1000, None),
    ])

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = IEasyDAClientExtension.PullItemChanged(client, 2*1000)
    if eventArgs is not None:
        # Handle the notification event
        if (eventArgs.Succeeded):
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq, sep='')
        else:
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief, sep='')

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

COM

// This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure PullItemChanged.MultipleItems;
var
  Arguments: OleVariant;
  Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
  EndTick: Cardinal;
  EventArgs: _EasyDAItemChangedEventArgs;
  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;

  // Intentionally specifying an unknown item here, to demonstrate its behavior.
  ItemSubscriptionArguments4 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments4.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments4.ItemDescriptor.ItemID := 'SomeUnknownItem';
  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
  Client := CoEasyDAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullItemChangedQueueCapacity := 1000;

  WriteLn('Subscribing item changes...');
  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(
    Client.SubscribeMultipleItems(Arguments));

  WriteLn('Processing item changes for 1 minute...');
  EndTick := Ticks + 60*1000;
  while Ticks < EndTick do
  begin
    EventArgs := Client.PullItemChanged(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      if eventArgs.Succeeded then
        WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq.ToString)
      else
        WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief);
  end;

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

  VarClear(HandleArray);
  VarClear(Arguments);

  WriteLn('Finished.');
end;

# This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
#
# The Python for Windows (pywin32) extensions package is needed. Install it using "pip install pypiwin32".
# CAUTION: We now recommend using Python.NET package instead. Full set of examples with Python.NET is available!
#
# Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
import time
import win32com.client

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient') 
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')

itemSubscriptionArguments1 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments1.ServerDescriptor.ServerClass = 'OPCLabs.KitServer.2'
itemSubscriptionArguments1.ItemDescriptor.ItemID = 'Simulation.Random'
itemSubscriptionArguments1.GroupParameters.RequestedUpdateRate = 1000

itemSubscriptionArguments2 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments2.ServerDescriptor.ServerClass = 'OPCLabs.KitServer.2'
itemSubscriptionArguments2.ItemDescriptor.ItemID = 'Trends.Ramp (1 min)'
itemSubscriptionArguments2.GroupParameters.RequestedUpdateRate = 1000

itemSubscriptionArguments3 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments3.ServerDescriptor.ServerClass = 'OPCLabs.KitServer.2'
itemSubscriptionArguments3.ItemDescriptor.ItemID = 'Trends.Sine (1 min)'
itemSubscriptionArguments3.GroupParameters.RequestedUpdateRate = 1000

# Intentionally specifying an unknown item here, to demonstrate its behavior.
itemSubscriptionArguments4 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments4.ServerDescriptor.ServerClass = 'OPCLabs.KitServer.2'
itemSubscriptionArguments4.ItemDescriptor.ItemID = 'UnknownItem'
itemSubscriptionArguments4.GroupParameters.RequestedUpdateRate = 1000

arguments = [
    itemSubscriptionArguments1,
    itemSubscriptionArguments2,
    itemSubscriptionArguments3,
    itemSubscriptionArguments4,
    ]
client.SubscribeMultipleItems(arguments)

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = client.PullItemChanged(2*1000)
    if eventArgs is not None:
        # Handle the notification event
        if (eventArgs.Succeeded):
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq, sep='')
        else:
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief, sep='')

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

REM This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.
REM
REM Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Private Sub PullItemChanged_MultipleItems_Command_Click()
    OutputText = ""
    
    Dim eventArgs As EasyDAItemChangedEventArgs
    
    Dim itemSubscriptionArguments1 As New EasyDAItemSubscriptionArguments
    itemSubscriptionArguments1.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    itemSubscriptionArguments1.ItemDescriptor.itemId = "Simulation.Random"
    itemSubscriptionArguments1.GroupParameters.requestedUpdateRate = 1000

    Dim itemSubscriptionArguments2 As New EasyDAItemSubscriptionArguments
    itemSubscriptionArguments2.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    itemSubscriptionArguments2.ItemDescriptor.itemId = "Trends.Ramp (1 min)"
    itemSubscriptionArguments2.GroupParameters.requestedUpdateRate = 1000

    Dim itemSubscriptionArguments3 As New EasyDAItemSubscriptionArguments
    itemSubscriptionArguments3.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    itemSubscriptionArguments3.ItemDescriptor.itemId = "Trends.Sine (1 min)"
    itemSubscriptionArguments3.GroupParameters.requestedUpdateRate = 1000

    ' Intentionally specifying an unknown item here, to demonstrate its behavior.
    Dim itemSubscriptionArguments4 As New EasyDAItemSubscriptionArguments
    itemSubscriptionArguments4.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    itemSubscriptionArguments4.ItemDescriptor.itemId = "SomeUnknownItem"
    itemSubscriptionArguments4.GroupParameters.requestedUpdateRate = 1000

    Dim arguments(3) As Variant
    Set arguments(0) = itemSubscriptionArguments1
    Set arguments(1) = itemSubscriptionArguments2
    Set arguments(2) = itemSubscriptionArguments3
    Set arguments(3) = itemSubscriptionArguments4

    ' Instantiate the client object
    Dim client As New EasyDAClient
    ' In order to use event pull, you must set a non-zero queue capacity upfront.
    client.PullItemChangedQueueCapacity = 1000

    OutputText = OutputText & "Subscribing item changes..." & vbCrLf
    Dim handleArray() As Variant
    handleArray = client.SubscribeMultipleItems(arguments)
    
    OutputText = OutputText & "Processing item changes for 1 minute..." & vbCrLf
    Dim endTick As Long
    endTick = GetTickCount + 60000
    While GetTickCount < endTick
        Set eventArgs = client.PullItemChanged(2 * 1000)
        If Not eventArgs Is Nothing Then
            ' Handle the notification event
            If eventArgs.Succeeded Then
                OutputText = OutputText & eventArgs.arguments.ItemDescriptor.itemId & ": " & eventArgs.vtq & vbCrLf
            Else
                OutputText = OutputText & eventArgs.arguments.ItemDescriptor.itemId & " *** Failure: " & eventArgs.ErrorMessageBrief & vbCrLf
            End If
        End If
    Wend
    
    OutputText = OutputText & "Unsubscribing item changes..." & vbCrLf
    client.UnsubscribeAllItems

    OutputText = OutputText & "Finished." & vbCrLf
End Sub
See Also
Examples - OPC Data Access - Subscribe to a single item
Examples - OPC Data Access - Subscribe to multiple items

Conceptual

Event Pull Mechanism
Subscribing to OPC Classic Items

Examples - OPC Unified Architecture

Examples - OPC Unified Architecture - Event pull of data change notifications

Examples - OPC Alarms&Events

Examples - OPC Alarms&Events - Event pull

Examples - OPC XML-DA

Examples - OPC XML-DA - Event pull

 

 

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