QuickOPC User's Guide and Reference
Examples - OPC Unified Architecture - Event pull of data change notifications
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClient
{
    class PullDataChangeNotification
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (not in .NET Standard)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyUAClient { PullDataChangeNotificationQueueCapacity = 1000 };

            Console.WriteLine("Subscribing...");
            client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000);

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

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();
        }
    }
}
# This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

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

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Assemblies/net47/OpcLabs.EasyOpcUA.dll"

[UAEndpointDescriptor]$endpointDescriptor =
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
# or "http://opcua.demo-this.com:51211/UA/SampleServer" (not in .NET Standard)
# or "https://opcua.demo-this.com:51212/UA/SampleServer/"

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

Write-Host "Subscribing..."
$client.SubscribeDataChange($endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

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

Write-Host "Unsubscribing..."
$client.UnsubscribeAllMonitoredItems()

Write-Host "Finished."
' This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace UADocExamples._EasyUAClient
    Friend Class PullDataChangeNotification
        Public Shared Sub Main1()

            ' Define which server we will work with.
            Dim endpointDescriptor As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' or "http://opcua.demo-this.com:51211/UA/SampleServer" (not in .NET Standard)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object
            Dim client = New EasyUAClient()
            ' In order to use event pull, you must set a non-zero queue capacity upfront.
            client.PullDataChangeNotificationQueueCapacity = 1000

            Console.WriteLine("Subscribing...")
            client.SubscribeDataChange(
                endpointDescriptor,
                "nsu=http://test.org/UA/Data/ ;i=10853",
                1000)   ' or "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"

            Console.WriteLine("Processing data change events for 1 minute...")
            Dim endTick As Integer = Environment.TickCount + 60 * 1000
            Do
                Dim eventArgs As EasyUADataChangeNotificationEventArgs = client.PullDataChangeNotification(2 * 1000)
                If Not eventArgs Is Nothing Then
                    ' Handle the notification event
                    Console.WriteLine(eventArgs)
                End If
            Loop While Environment.TickCount < endTick
        End Sub
    End Class
End Namespace
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

class procedure PullDataChangeNotification.Main;
var
  Client: EasyUAClient;
  EndTick: Cardinal;
  EventArgs: _EasyUADataChangeNotificationEventArgs;
begin
  // Instantiate the client object
  Client := CoEasyUAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullDataChangeNotificationQueueCapacity := 1000;

  WriteLn('Subscribing...');
  Client.SubscribeDataChange(
    'http://opcua.demo-this.com:51211/UA/SampleServer',
    'nsu=http://test.org/UA/Data/ ;i=10853',
    1000);

  WriteLn('Processing data change events for 1 minute...');
  EndTick := GetTickCount + 60*1000;
  while GetTickCount < EndTick do
  begin
    EventArgs := Client.PullDataChangeNotification(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      WriteLn(EventArgs.ToString);
  end;

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

  WriteLn('Finished.');
end;
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

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

WScript.Echo("Subscribing...");
Client.SubscribeDataChange("http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000);

WScript.Echo("Processing data change events for 1 minute...");
var endTime = new Date().getTime() + 60*1000
do {
    var EventArgs = Client.PullDataChangeNotification(2*1000);
    if (EventArgs !== null) {
        //  Handle the notification event
        WScript.Echo(EventArgs);
    }
} while(new Date().getTime() < endTime);
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

class procedure PullDataChangeNotification.Main;
var
  Client: OpcLabs_EasyOpcUA_TLB._EasyUAClient;
  EndTick: Cardinal;
  EventArgs: _EasyUADataChangeNotificationEventArgs;
begin
  // Instantiate the client object
  Client := CoEasyUAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullDataChangeNotificationQueueCapacity := 1000;

  WriteLn('Subscribing...');
  Client.SubscribeDataChange(
    'http://opcua.demo-this.com:51211/UA/SampleServer',
    'nsu=http://test.org/UA/Data/ ;i=10853',
    1000);

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

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

  WriteLn('Finished.');
end;
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

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

print "Subscribing...\n";
$Client->SubscribeDataChange("http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000);

print "Processing data change events for 1 minute...\n";
$endTime = time() + 60;
do {
    $EventArgs = $Client->PullDataChangeNotification(2*1000);
    if (!is_null($EventArgs)) {
        // Handle the notification event
        print $EventArgs->ToString();
        print "\n";
    }
} while (time() < $endTime);
// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

mle_outputtext.Text = ""

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

mle_outputtext.Text = mle_outputtext.Text + "Subscribing data changes..." + "~r~n"
client.SubscribeDataChange("http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

mle_outputtext.Text = mle_outputtext.Text + "Processing data change events for 1 minute..." + "~r~n"

Time endTime = RelativeTime(Now(), 60)
DO
    OLEObject eventArgs
    eventArgs = client.PullDataChangeNotification(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 + "~r~n" 
mle_outputtext.Text = mle_outputtext.Text + "Finished." + "~r~n" 
# This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

import time
import win32com.client

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

print('Subscribing...')
client.SubscribeDataChange('http://opcua.demo-this.com:51211/UA/SampleServer', 'nsu=http://test.org/UA/Data/ ;i=10853', 1000)

print('Processing data change events for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = client.PullDataChangeNotification(2*1000)
    if eventArgs is not None:
        # Handle the notification event
        print(eventArgs)
Rem This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

Public Sub PullDataChangeNotification_Main_Command_Click()
    OutputText = ""
    
    Dim eventArgs As EasyUADataChangeNotificationEventArgs
    
    ' Instantiate the client object
    Dim Client As New EasyUAClient
    
    ' In order to use event pull, you must set a non-zero queue capacity upfront.
    Client.PullDataChangeNotificationQueueCapacity = 1000
    
    OutputText = OutputText & "Subscribing..." & vbCrLf
    Call Client.SubscribeDataChange("http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

    OutputText = OutputText & "Processing data changed notification events for 1 minute..." & vbCrLf
    
    Dim EndTick As Long
    EndTick = GetTickCount + 60000
    While GetTickCount < EndTick
        Set eventArgs = Client.PullDataChangeNotification(2 * 1000)
        If Not eventArgs Is Nothing Then
            ' Handle the notification event
            OutputText = OutputText & eventArgs & vbCrLf
        End If
    Wend
    
    OutputText = OutputText & "Unsubscribing..." & vbCrLf
    Client.UnsubscribeAllMonitoredItems

    OutputText = OutputText & "Finished." & vbCrLf
End Sub
Rem This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

Option Explicit

' Instantiate the client object
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")
' In order to use event pull, you must set a non-zero queue capacity upfront.
Client.PullDataChangeNotificationQueueCapacity = 1000

WScript.Echo "Subscribing..."
Client.SubscribeDataChange "http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000

WScript.Echo "Processing data change events for 1 minute..."
Dim endTime: endTime = Now() + 60*(1/24/60/60)
Do
    Dim EventArgs: Set EventArgs = Client.PullDataChangeNotification(2*1000)
    If Not (EventArgs Is Nothing) Then
        ' Handle the notification event
        WScript.Echo EventArgs
    End If    
Loop While Now() < endTime
* This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

DECLARE INTEGER GetTickCount IN kernel32 

THISFORM.OutputEdit.Value = ""

* Instantiate the client object.
oClient = CREATEOBJECT("OpcLabs.EasyOpc.UA.EasyUAClient")

* In order to use event pull, you must set a non-zero queue capacity upfront.
oClient.PullDataChangeNotificationQueueCapacity = 1000

THISFORM.OutputEdit.Value = THISFORM.OutputEdit.Value + "Subscribing..." + CHR(13) + CHR(10)
oClient.SubscribeDataChange("http://opcua.demo-this.com:51211/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

THISFORM.OutputEdit.Value = THISFORM.OutputEdit.Value + "Processing data change notification events for 1 minute..." + CHR(13) + CHR(10)

EndTick = GetTickCount() + 60000
DO WHILE GetTickCount() < EndTick
    oEventArgs = oClient.PullDataChangeNotification(2*1000)
    IF NOT ISNULL(oEventArgs)
        THISFORM.OutputEdit.Value = THISFORM.OutputEdit.Value + oEventArgs.DisplayString + CHR(13) + CHR(10)
    ENDIF
ENDDO

THISFORM.OutputEdit.Value = THISFORM.OutputEdit.Value + "Unsubscribing..." + CHR(13) + CHR(10)
oClient.UnsubscribeAllMonitoredItems()

THISFORM.OutputEdit.Value = THISFORM.OutputEdit.Value + "Finished." + CHR(13) + CHR(10)
See Also

Conceptual

Examples - OPC Alarms&Events

Examples - OPC UA Alarms&Conditions