Trigger Property (UADataChangeFilter)

Specifies the conditions under which a data change notification should be reported.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<DefaultValueAttribute(Mono.Cecil.CustomAttributeArgument)>
Public Property Trigger As UADataChangeTrigger

'Usage
 
Dim instance As UADataChangeFilter
Dim value As UADataChangeTrigger
 
instance.Trigger = value
 
value = instance.Trigger

[DefaultValue(Mono.Cecil.CustomAttributeArgument)]
public UADataChangeTrigger Trigger {get; set;}

[DefaultValue(Mono.Cecil.CustomAttributeArgument)]
public:
property UADataChangeTrigger Trigger {
   UADataChangeTrigger get();
   void set (    UADataChangeTrigger value);
}

Remarks

In order to obtain or modify this parameter, access the UAMonitoringParameters.DataChangeFilter property of OpcLabs.EasyOpc.UA.OperationModel.UAMonitoredItemArguments.MonitoringParameters.

Example

.NET

COM

.NET

// This example shows how to subscribe to changes of a monitored item with data change filter.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeDataChange
    {
        public static void Filter()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object and hook events.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification_Filter;

            Console.WriteLine("Subscribing...");
            // Report a notification if either the StatusCode or the value change. 
            // The UADataChangeTrigger has an implicit conversion to UADataChangeFilter and can thus be used in its place.
            client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000, 
                dataChangeFilter:UADataChangeTrigger.StatusValue);

            Console.WriteLine("Processing data change events for 20 seconds...");
            System.Threading.Thread.Sleep(20 * 1000);

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void client_DataChangeNotification_Filter(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value.
            if (e.Succeeded)
                Console.WriteLine($"Value: {e.AttributeData.Value}");
            else
                Console.WriteLine($"*** Failure: {e.ErrorMessageBrief}");
        }
    }
}

# This example shows how to subscribe to changes of a monitored item with data change filter.

#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 "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUA.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUAComponents.dll"

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

# Instantiate the client object.
$client = New-Object EasyUAClient

# Data change notification handler
Register-ObjectEvent -InputObject $client -EventName DataChangeNotification -Action { 
    # Display value.
    if ($EventArgs.Succeeded) {
        Write-Host "Value: $($EventArgs.AttributeData.Value)"
    }
    else {
        Write-Host "*** Failure: $($EventArgs.ErrorMessageBrief)"
    }
}

Write-Host "Subscribing..."
# Report a notification if either the StatusCode or the value change. 
# The UADataChangeTrigger has an implicit conversion to UADataChangeFilter and can thus be used in its place.
[IEasyUAClientExtension]::SubscribeDataChange($client, $endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000,
    [UADataChangeTrigger]::StatusValue)

Write-Host "Processing data change events for 20 seconds..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 20) {    
    Start-Sleep -Seconds 1
}

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

Write-Host "Waiting for 5 seconds..."
Start-Sleep -Seconds 5

Write-Host "Finished."

# This example shows how to subscribe to changes of a monitored item with data change filter.

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

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


def dataChangeNotification(sender, e):
    # Display value.
    if e.Succeeded:
        print('Value: ', e.AttributeData.Value, sep='')
    else:
        print('*** Failure: ', e.ErrorMessageBrief, sep='')


endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'

# Instantiate the client object and hook events.
client = EasyUAClient()
client.DataChangeNotification += dataChangeNotification

print('Subscribing...')
# Report a notification if either the StatusCode or the value change.
# The UADataChangeTrigger has an implicit conversion to UADataChangeFilter.
IEasyUAClientExtension.SubscribeDataChange(client,
    endpointDescriptor,
    UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'),
    1000,
    UADataChangeFilter(UADataChangeTrigger.StatusValue))

print('Processing data change events for 20 seconds...')
time.sleep(20)

print('Unsubscribing...')
client.UnsubscribeAllMonitoredItems()

print('Waiting for 5 seconds...')
time.sleep(5)

print('Finished.')

' This example shows how to subscribe to changes of a monitored item with data change filter.

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

Namespace _EasyUAClient
    Partial Friend Class SubscribeDataChange
        Public Shared Sub Filter()

            ' 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" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object and hook events
            Dim client = New EasyUAClient()
            AddHandler client.DataChangeNotification, AddressOf client_DataChangeNotification_Filter

            Console.WriteLine("Subscribing...")
            ' Report a notification if either the StatusCode Or the value change. 
            ' The UADataChangeTrigger has an implicit conversion to UADataChangeFilter And can thus be used in its place.
            client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000, UADataChangeTrigger.StatusValue)

            Console.WriteLine("Processing data change events for 20 seconds...")
            Threading.Thread.Sleep(20 * 1000)

            Console.WriteLine("Unsubscribing...")
            client.UnsubscribeAllMonitoredItems()

            Console.WriteLine("Waiting for 5 seconds...")
            Threading.Thread.Sleep(5 * 1000)
        End Sub

        Private Shared Sub client_DataChangeNotification_Filter(ByVal sender As Object, ByVal e As EasyUADataChangeNotificationEventArgs)
            ' Display value
            If e.Succeeded Then
                Console.WriteLine("Value: {0}", e.AttributeData.Value)
            Else
                Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief)
            End If
        End Sub
    End Class
End Namespace

Object Pascal
PHP
VBScript
Visual Basic (VB 6.0)

// This example shows how to subscribe to changes of a monitored item
// with data change filter.

type
  TClientEventHandlers120 = class
    procedure Client_DataChangeNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUADataChangeNotificationEventArgs);
  end;

procedure TClientEventHandlers120.Client_DataChangeNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUADataChangeNotificationEventArgs);
begin
  // Display the data
  if eventArgs.Succeeded then
  begin
      WriteLn(eventArgs.AttributeData.ToString);
  end
  else
      WriteLn(' *** Failure: ', eventArgs.ErrorMessageBrief);
end;

class procedure SubscribeDataChange.Filter;
const
  UADataChangeFilter_StatusValue = 1;
var
  Arguments: OleVariant;
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers120;
  DataChangeFilter: _UADataChangeFilter;
  EndpointDescriptor: string;
  MonitoringItemArguments1: _EasyUAMonitoredItemArguments;
  MonitoringParameters:  _UAMonitoringParameters;
begin
  EndpointDescriptor := 
    //'http://opcua.demo-this.com:51211/UA/SampleServer';
    //'https://opcua.demo-this.com:51212/UA/SampleServer/';
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer';

  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers120.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.Client_DataChangeNotification;

  // Prepare the arguments.
  // Report a notification if either the StatusCode or the value change.
  DataChangeFilter := CoUADataChangeFilter.Create;
  DataChangeFilter.Trigger := UADataChangeFilter_StatusValue;
  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.DataChangeFilter := DataChangeFilter;
  MonitoringParameters.SamplingInterval := 100;
  MonitoringItemArguments1 := CoEasyUAMonitoredItemArguments.Create;
  MonitoringItemArguments1.EndpointDescriptor.UrlString := EndpointDescriptor;
  MonitoringItemArguments1.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/ ;i=10853';
  MonitoringItemArguments1.MonitoringParameters := MonitoringParameters;

  Arguments := VarArrayCreate([0, 0], varVariant);
  Arguments[0] := MonitoringItemArguments1;

  WriteLn('Subscribing...');
  Client.SubscribeMultipleMonitoredItems(arguments);

  WriteLn('Processing monitored item changed events for 20 seconds...');
  PumpSleep(20*1000);

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

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

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

// This example shows how to subscribe to changes of a monitored item
// with data change filter.

class ClientEvents {
    function DataChangeNotification($Sender, $E)
    {
        // Display the data
        if ($E->Succeeded)
            printf("%s\n", $E->AttributeData);
        else
            printf(" *** Failure: %s\n", $E->ErrorMessageBrief);
    }
}

const UADataChangeFilter_StatusValue = 1;

$EndpointDescriptor = new COM("OpcLabs.EasyOpc.UA.UAEndpointDescriptor");
$EndpointDescriptor->UrlString = 
    //"http://opcua.demo-this.com:51211/UA/SampleServer";
    //"https://opcua.demo-this.com:51212/UA/SampleServer/";
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";


// Instantiate the client object and hook events
$Client = new COM("OpcLabs.EasyOpc.UA.EasyUAClient");
$ClientEvents = new ClientEvents();
com_event_sink($Client, $ClientEvents, "DEasyUAClientEvents");

// Prepare the arguments.
// Report a notification if either the StatusCode or the value change.
$DataChangeFilter = new COM("OpcLabs.EasyOpc.UA.UADataChangeFilter");
$DataChangeFilter->Trigger = UADataChangeFilter_StatusValue;
$MonitoringParameters = new COM("OpcLabs.EasyOpc.UA.UAMonitoringParameters");
$MonitoringParameters->DataChangeFilter = $DataChangeFilter;
$MonitoringParameters->SamplingInterval = 100;
$MonitoredItemArguments1 = new COM("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments");
$MonitoredItemArguments1->EndpointDescriptor->UrlString = $EndpointDescriptor;
$MonitoredItemArguments1->NodeDescriptor->NodeId->ExpandedText = "nsu=http://test.org/UA/Data/ ;i=10853";
$MonitoredItemArguments1->MonitoringParameters = $MonitoringParameters;
$arguments[0] = $MonitoredItemArguments1;

printf("Subscribing...\n");
$Client->SubscribeMultipleMonitoredItems($arguments);

printf("Processing monitored item changed events for 20 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 20);

printf("Unsubscribing...\n");
$Client->UnsubscribeAllMonitoredItems;

printf("Waiting for 5 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 5);

Rem This example shows how to subscribe to changes of a monitored item with data change filter.

Option Explicit

Const UADataChangeTrigger_StatusValue = 1

Dim endpointDescriptor: endpointDescriptor = _
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    '"http://opcua.demo-this.com:51211/UA/SampleServer"  
    '"https://opcua.demo-this.com:51212/UA/SampleServer/"

' Instantiate the client object and hook events
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")
WScript.ConnectObject Client, "Client_"

' Prepare the arguments.
' Report a notification if either the StatusCode or the value change. 
Dim DataChangeFilter: Set DataChangeFilter = CreateObject("OpcLabs.EasyOpc.UA.UADataChangeFilter")
DataChangeFilter.Trigger = UADataChangeTrigger_StatusValue
'
Dim MonitoringParameters: Set MonitoringParameters = CreateObject("OpcLabs.EasyOpc.UA.UAMonitoringParameters")
Set MonitoringParameters.DataChangeFilter = DataChangeFilter
MonitoringParameters.SamplingInterval = 1000
'
Dim MonitoredItemArguments1: Set MonitoredItemArguments1 = CreateObject("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments")
MonitoredItemArguments1.EndpointDescriptor.UrlString = endpointDescriptor
MonitoredItemArguments1.NodeDescriptor.NodeId.ExpandedText = "nsu=http://test.org/UA/Data/ ;i=10853"
MonitoredItemArguments1.MonitoringParameters = MonitoringParameters
'
Dim arguments(0)
Set arguments(0) = MonitoredItemArguments1

WScript.Echo "Subscribing..."
Client.SubscribeMultipleMonitoredItems arguments

WScript.Echo "Processing monitored item changed events for 20 seconds..."
WScript.Sleep 20*1000

WScript.Echo "Unsubscribing..."
Client.UnsubscribeAllMonitoredItems

WScript.Echo "Waiting for 5 seconds..."
WScript.Sleep 5 * 1000



Sub Client_DataChangeNotification(Sender, e)
    ' Display value
    Dim display: If e.Exception Is Nothing Then display = e.AttributeData Else display = "*** Failure: " & e.ErrorMessageBrief
    WScript.Echo display
End Sub

Rem This example shows how to subscribe to changes of a monitored item with data change filter.

' The client object, with events
'Public WithEvents Client3 As EasyUAClient

Public Sub SubscribeDataChange_Filter_Command_Click()
    OutputText = ""

    Dim endpointDescriptor As String
    'endpointDescriptor = "http://opcua.demo-this.com:51211/UA/SampleServer"
    'endpointDescriptor = "https://opcua.demo-this.com:51212/UA/SampleServer/"
    endpointDescriptor = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"

    ' Instantiate the client object and hook events
    Set Client3 = New EasyUAClient
    
    ' Prepare the arguments.
    ' Report a notification if either the StatusCode or the value change.
    Dim DataChangeFilter As New UADataChangeFilter
    DataChangeFilter.Trigger = UADataChangeTrigger_StatusValue
    
    Dim MonitoringParameters As New UAMonitoringParameters
    Set MonitoringParameters.DataChangeFilter = DataChangeFilter
    MonitoringParameters.SamplingInterval = 1000
    
    Dim MonitoredItemArguments1 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments1.endpointDescriptor.UrlString = endpointDescriptor
    MonitoredItemArguments1.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10853"
    Set MonitoredItemArguments1.MonitoringParameters = MonitoringParameters

    Dim arguments(0) As Variant
    Set arguments(0) = MonitoredItemArguments1

    OutputText = OutputText & "Subscribing..." & vbCrLf
    Call Client3.SubscribeMultipleMonitoredItems(arguments)

    OutputText = OutputText & "Processing monitored item changed events for 20 seconds..." & vbCrLf
    Pause 20000

    OutputText = OutputText & "Unsubscribing..." & vbCrLf
    Client3.UnsubscribeAllMonitoredItems

    OutputText = OutputText & "Waiting for 5 seconds..." & vbCrLf
    Pause 5000

    Set Client3 = Nothing
End Sub

Public Sub Client3_DataChangeNotification(ByVal sender As Variant, ByVal eventArgs As EasyUADataChangeNotificationEventArgs)
    ' Display the data
    If eventArgs.Exception Is Nothing Then
        OutputText = OutputText & eventArgs.AttributeData & vbCrLf
    Else
        OutputText = OutputText & eventArgs.ErrorMessageBrief & vbCrLf
    End If
End Sub

CSharp
PowerShell
Python
VB.NET

// This example shows how to subscribe to changes of multiple monitored items and use a data change filter.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeMultipleMonitoredItems
    {
        public static void Filter()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object and hook events.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification_Filter;

            Console.WriteLine("Subscribing...");
            // Report a notification if either the StatusCode or the value change. 
            // The UADataChangeTrigger has an implicit conversion to UADataChangeFilter and can thus be used in its place.
            client.SubscribeMultipleMonitoredItems(new[]
                {
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10845", 
                        new UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue)),
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10853", 
                        new UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue)),
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10855", 
                        new UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue))
                });

            Console.WriteLine("Processing monitored item changed events for 10 seconds...");
            System.Threading.Thread.Sleep(10 * 1000);

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void client_DataChangeNotification_Filter(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value.
            if (e.Succeeded)
                Console.WriteLine($"{e.Arguments.NodeDescriptor}: {e.AttributeData.Value}");
            else
                Console.WriteLine($"{e.Arguments.NodeDescriptor} *** Failure: {e.ErrorMessageBrief}");
        }
    }
}

# This example shows how to subscribe to changes of multiple monitored items and use a data change filter.

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

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

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

# Instantiate the client object.
$client = New-Object EasyUAClient

# Data change notification handler
Register-ObjectEvent -InputObject $client -EventName DataChangeNotification -Action { 
    # Display value.
    if ($EventArgs.Succeeded) {
        Write-Host "$($EventArgs.Arguments.NodeDescriptor): $($EventArgs.AttributeData.Value)"
    }
    else {
        Write-Host "$($EventArgs.Arguments.NodeDescriptor) *** Failure: $($EventArgs.ErrorMessageBrief)"
    }
}

Write-Host "Subscribing..."
# Report a notification if either the StatusCode or the value change. 
# The UADataChangeTrigger has an implicit conversion to UADataChangeFilter and can thus be used in its place.
$handleArray = $client.SubscribeMultipleMonitoredItems(@(
    (New-Object UAMonitoredItemArguments(
        (New-Object UAAttributeArguments($endpointDescriptor, [UANodeDescriptor]"nsu=http://test.org/UA/Data/ ;i=10845")), 
        (New-Object UAMonitoringParameters(1000, [UADataChangeTrigger]::StatusValue)))),
    (New-Object UAMonitoredItemArguments(
        (New-Object UAAttributeArguments($endpointDescriptor, [UANodeDescriptor]"nsu=http://test.org/UA/Data/ ;i=10853")), 
        (New-Object UAMonitoringParameters(1000, [UADataChangeTrigger]::StatusValue)))),
    (New-Object UAMonitoredItemArguments(
        (New-Object UAAttributeArguments($endpointDescriptor, [UANodeDescriptor]"nsu=http://test.org/UA/Data/ ;i=10855")),
        (New-Object UAMonitoringParameters(1000, [UADataChangeTrigger]::StatusValue))))
    ))

Write-Host
Write-Host "Processing monitored item changed events for 10 seconds..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 10) {    
    Start-Sleep -Seconds 1
}

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

Write-Host "Waiting for 5 seconds..."
Start-Sleep -Seconds 5

Write-Host "Finished."

# This example shows how to subscribe to changes of multiple monitored items and use a data change filter.

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

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


def dataChangeNotification(sender, e):
    # Display value.
    if e.Succeeded:
        print(e.Arguments.NodeDescriptor, ': ', e.AttributeData.Value, sep='')
    else:
        print(e.Arguments.NodeDescriptor, ' *** Failure: ', e.ErrorMessageBrief, sep='')


endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'

# Instantiate the client object and hook events.
client = EasyUAClient()
client.DataChangeNotification += dataChangeNotification

print('Subscribing...')
# Report a notification if either the StatusCode or the value change.
# The UADataChangeTrigger has an implicit conversion to UADataChangeFilter.
client.SubscribeMultipleMonitoredItems([
    EasyUAMonitoredItemArguments(
        None,
        endpointDescriptor,
        UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10845'),
        UAMonitoringParameters(1000, UADataChangeFilter(UADataChangeTrigger.StatusValue))),
    EasyUAMonitoredItemArguments(
        None,
        endpointDescriptor,
        UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'),
        UAMonitoringParameters(1000, UADataChangeFilter(UADataChangeTrigger.StatusValue))),
    EasyUAMonitoredItemArguments(
        None,
        endpointDescriptor,
        UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10855'),
        UAMonitoringParameters(1000, UADataChangeFilter(UADataChangeTrigger.StatusValue))),
    ])

print('Processing data change events for 10 seconds...')
time.sleep(10)

print('Unsubscribing...')
client.UnsubscribeAllMonitoredItems()

print('Waiting for 5 seconds...')
time.sleep(5)

print('Finished.')

' This example shows how to subscribe to changes of multiple monitored items and use a data change filter.

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

Namespace _EasyUAClient
    Partial Friend Class SubscribeMultipleMonitoredItems
        Public Shared Sub Filter()

            ' 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" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object and hook events
            Dim client = New EasyUAClient()
            AddHandler client.DataChangeNotification, AddressOf client_DataChangeNotification_Filter

            Console.WriteLine("Subscribing...")
            ' Report a notification if either the StatusCode Or the value change. 
            ' The UADataChangeTrigger has an implicit conversion to UADataChangeFilter And can thus be used in its place.
            client.SubscribeMultipleMonitoredItems(New EasyUAMonitoredItemArguments() _
                {
                    New EasyUAMonitoredItemArguments(Nothing, endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10845", New UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue)),
                    New EasyUAMonitoredItemArguments(Nothing, endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", New UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue)),
                    New EasyUAMonitoredItemArguments(Nothing, endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10855", New UAMonitoringParameters(1000, UADataChangeTrigger.StatusValue))
                }
             )

            Console.WriteLine("Processing monitored item changed events for 10 seconds...")
            Threading.Thread.Sleep(10 * 1000)

            Console.WriteLine("Unsubscribing...")
            client.UnsubscribeAllMonitoredItems()

            Console.WriteLine("Waiting for 5 seconds...")
            Threading.Thread.Sleep(5 * 1000)
        End Sub

        Private Shared Sub client_DataChangeNotification_Filter(ByVal sender As Object, ByVal e As EasyUADataChangeNotificationEventArgs)
            ' Display value
            If e.Succeeded Then
                Console.WriteLine("{0}: {1}", e.Arguments.NodeDescriptor, e.AttributeData.Value)
            Else
                Console.WriteLine("{0} *** Failure: {1}", e.Arguments.NodeDescriptor, e.ErrorMessageBrief)
            End If
        End Sub
    End Class
End Namespace

Object Pascal
PHP
Visual Basic (VB 6.0)

// This example shows how to subscribe to changes of multiple monitored items
// and use a data change filter.

type
  TClientEventHandlers122 = class
    procedure OnDataChangeNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUADataChangeNotificationEventArgs);
  end;

procedure TClientEventHandlers122.OnDataChangeNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUADataChangeNotificationEventArgs);
begin
  // Display the data
  if eventArgs.Succeeded then
      WriteLn(eventArgs.Arguments.NodeDescriptor.ToString, ': ',
      eventArgs.AttributeData.ToString)
  else
      WriteLn(eventArgs.Arguments.NodeDescriptor.ToString, ' *** Failure: ',
      eventArgs.ErrorMessageBrief);
end;

class procedure SubscribeMultipleMonitoredItems.Filter;
const
  UADataChangeFilter_StatusValue = 1;
var
  Arguments: OleVariant;
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers122;
  DataChangeFilter: _UADataChangeFilter;
  HandleArray: OleVariant;
  MonitoredItemArguments1, MonitoredItemArguments2, MonitoredItemArguments3:
    _EasyUAMonitoredItemArguments;
  MonitoringParameters: _UAMonitoringParameters;
begin
  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers122.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.OnDataChangeNotification;

  // Prepare the arguments.
  // Report a notification if either the StatusCode or the value change.
  DataChangeFilter := CoUADataChangeFilter.Create;
  DataChangeFilter.Trigger := UADataChangeFilter_StatusValue;

  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.DataChangeFilter := DataChangeFilter;
  MonitoringParameters.SamplingInterval := 1000;
  MonitoredItemArguments1 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments1.EndpointDescriptor.UrlString := 
    //'http://opcua.demo-this.com:51211/UA/SampleServer';
    //'https://opcua.demo-this.com:51212/UA/SampleServer/';
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer';
  MonitoredItemArguments1.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/ ;i=10845';
  MonitoredItemArguments1.MonitoringParameters := MonitoringParameters;
  MonitoredItemArguments2 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments2.EndpointDescriptor.UrlString := 
    //'http://opcua.demo-this.com:51211/UA/SampleServer';
    //'https://opcua.demo-this.com:51212/UA/SampleServer/';
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer';
  MonitoredItemArguments2.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/ ;i=10853';
  MonitoredItemArguments2.MonitoringParameters := MonitoringParameters;
  MonitoredItemArguments3 := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments3.EndpointDescriptor.UrlString := 
    //'http://opcua.demo-this.com:51211/UA/SampleServer';
    //'https://opcua.demo-this.com:51212/UA/SampleServer/';
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer';
  MonitoredItemArguments3.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/ ;i=10855';
  MonitoredItemArguments3.MonitoringParameters := MonitoringParameters;
  Arguments := VarArrayCreate([0, 2], varVariant);
  Arguments[0] := MonitoredItemArguments1;
  Arguments[1] := MonitoredItemArguments2;
  Arguments[2] := MonitoredItemArguments3;

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

  WriteLn('Processing monitored item changed events for 10 seconds...');
  PumpSleep(10*1000);

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

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

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

// This example shows how to subscribe to changes of multiple monitored items
// and use a data change filter.

class ClientEvents {
    function DataChangeNotification($Sender, $E)
    {
        // Display the data
        if ($E->Succeeded)
            printf(" s\n", $E->Arguments->NodeDescriptor, $E->AttributeData);
        else
            printf("s *** Failures\n", $E->Arguments->NodeDescriptor, $E->ErrorMessageBrief);
    }
}

const UADataChangeFilter_StatusValue = 1;

// Instantiate the client object and hook events
$Client = new COM("OpcLabs.EasyOpc.UA.EasyUAClient");
$ClientEvents = new ClientEvents();
com_event_sink($Client, $ClientEvents, "DEasyUAClientEvents");

// Prepare the arguments.
// Report a notification if either the StatusCode or the value change.
$DataChangeFilter = new COM("OpcLabs.EasyOpc.UA.UADataChangeFilter");
$DataChangeFilter->Trigger = UADataChangeFilter_StatusValue;
$MonitoringParameters = new COM("OpcLabs.EasyOpc.UA.UAMonitoringParameters");
$MonitoringParameters->DataChangeFilter = $DataChangeFilter;
$MonitoringParameters->SamplingInterval = 1000;
$MonitoredItemArguments1 = new COM("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments");
$MonitoredItemArguments1->EndpointDescriptor->UrlString = 
    //"http://opcua.demo-this.com:51211/UA/SampleServer";
    //"https://opcua.demo-this.com:51212/UA/SampleServer/";
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
$MonitoredItemArguments1->NodeDescriptor->NodeId->ExpandedText = "nsu=http://test.org/UA/Data/ ;i=10845";
$MonitoredItemArguments1->MonitoringParameters = $MonitoringParameters;
$MonitoredItemArguments2 = new COM("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments");
$MonitoredItemArguments2->EndpointDescriptor->UrlString = 
    //"http://opcua.demo-this.com:51211/UA/SampleServer";
    //"https://opcua.demo-this.com:51212/UA/SampleServer/";
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
$MonitoredItemArguments2->NodeDescriptor->NodeId->ExpandedText = "nsu=http://test.org/UA/Data/ ;i=10853";
$MonitoredItemArguments2->MonitoringParameters = $MonitoringParameters;
$MonitoredItemArguments3 = new COM("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments");
$MonitoredItemArguments3->EndpointDescriptor->UrlString = 
    //"http://opcua.demo-this.com:51211/UA/SampleServer";
    //"https://opcua.demo-this.com:51212/UA/SampleServer/";
    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
$MonitoredItemArguments3->NodeDescriptor->NodeId->ExpandedText = "nsu=http://test.org/UA/Data/ ;i=10855";
$MonitoredItemArguments3->MonitoringParameters = $MonitoringParameters;
$arguments[0] = $MonitoredItemArguments1;
$arguments[1] = $MonitoredItemArguments2;
$arguments[2] = $MonitoredItemArguments3;

printf("Subscribing...\n");
$handleArray = $Client->SubscribeMultipleMonitoredItems($arguments);

for ($i = 0; $i < count($handleArray); $i++)
{
    printf("handleArray[d]d\n", $i, $handleArray[$i]);
}

printf("Processing monitored item changed events for 10 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 10);

printf("Unsubscribing...\n");
$Client->UnsubscribeAllMonitoredItems;

printf("Waiting for 5 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 5);

Rem This example shows how to subscribe to changes of multiple monitored items
Rem and use a data change filter.

' The client object, with events
'Public WithEvents Client4 As EasyUAClient

Public Sub SubscribeMultipleMonitoredItems_Filter_Command_Click()
    OutputText = ""

    ' Instantiate the client object and hook events
    Set Client4 = New EasyUAClient

    ' Prepare the arguments.
    ' Report a notification if either the StatusCode or the value change.
    Dim DataChangeFilter As New UADataChangeFilter
    DataChangeFilter.Trigger = UADataChangeTrigger_StatusValue
    '
    Dim MonitoringParameters As New UAMonitoringParameters
    Set MonitoringParameters.DataChangeFilter = DataChangeFilter
    MonitoringParameters.SamplingInterval = 1000
    
    Dim MonitoredItemArguments1 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments1.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments1.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10845"
    Set MonitoredItemArguments1.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments1.SetState ("Item1")
    
    Dim MonitoredItemArguments2 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments2.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments2.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10853"
    Set MonitoredItemArguments2.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments2.SetState ("Item2")
    
    Dim MonitoredItemArguments3 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments3.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments3.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10855"
    Set MonitoredItemArguments3.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments3.SetState ("Item3")
    
    Dim arguments(2) As Variant
    Set arguments(0) = MonitoredItemArguments1
    Set arguments(1) = MonitoredItemArguments2
    Set arguments(2) = MonitoredItemArguments3
    
    OutputText = OutputText & "Subscribing..." & vbCrLf
    Dim handleArray As Variant
    handleArray = Client4.SubscribeMultipleMonitoredItems(arguments)

    Dim i As Long: For i = LBound(handleArray) To UBound(handleArray)
        OutputText = OutputText & "handleArray(" & i & "): " & handleArray(i) & vbCrLf
    Next

    OutputText = OutputText & "Processing monitored item changed events for 10 seconds..." & vbCrLf
    Pause 10000

    OutputText = OutputText & "Unsubscribing..." & vbCrLf
    Call Client4.UnsubscribeAllMonitoredItems

    OutputText = OutputText & "Waiting for 5 seconds..." & vbCrLf
    Pause 5000

    Set Client4 = Nothing
    OutputText = OutputText & "Finished." & vbCrLf
End Sub

Public Sub Client4_DataChangeNotification(ByVal sender As Variant, ByVal eventArgs As EasyUADataChangeNotificationEventArgs)
    ' Display the data
    If eventArgs.Exception Is Nothing Then
        OutputText = OutputText & "[" & eventArgs.arguments.State & "] " & eventArgs.arguments.nodeDescriptor & ": " & eventArgs.AttributeData & vbCrLf
    Else
        OutputText = OutputText & "[" & eventArgs.arguments.State & "] " & eventArgs.arguments.nodeDescriptor & ": " & eventArgs.ErrorMessageBrief & vbCrLf
    End If
End Sub

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

Reference

UADataChangeFilter Class
UADataChangeFilter Members

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