QuickOPC User's Guide and Reference
SubscribeDataChange(IEasyUAClient,UAEndpointDescriptor,UANodeDescriptor,Int32) Method
Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA Namespace > IEasyUAClientExtension Class > SubscribeDataChange Method : SubscribeDataChange(IEasyUAClient,UAEndpointDescriptor,UANodeDescriptor,Int32) Method
The client object that will perform the operation.
Endpoint descriptor. Identifies the OPC-UA server.
Node descriptor. Identifies the node in OPC server's address space.
The sampling interval (in milliseconds) indicates the fastest rate at which the Server should sample its underlying source for data changes.
Subscribe to a data change. Specify an endpoint descriptor, node id, and sampling interval.
Syntax
'Declaration
 

<ExtensionAttribute()>
Public Overloads Shared Function SubscribeDataChange( _
   ByVal client As IEasyUAClient, _
   ByVal endpointDescriptor As UAEndpointDescriptor, _
   ByVal nodeDescriptor As UANodeDescriptor, _
   ByVal samplingInterval As Integer _
) As Integer
'Usage
 

Dim client As IEasyUAClient
Dim endpointDescriptor As UAEndpointDescriptor
Dim nodeDescriptor As UANodeDescriptor
Dim samplingInterval As Integer
Dim value As Integer
 
value = IEasyUAClientExtension.SubscribeDataChange(client, endpointDescriptor, nodeDescriptor, samplingInterval)
[Extension()]
public static int SubscribeDataChange( 
   IEasyUAClient client,
   UAEndpointDescriptor endpointDescriptor,
   UANodeDescriptor nodeDescriptor,
   int samplingInterval
)
[Extension()]
public:
static int SubscribeDataChange( 
   IEasyUAClient^ client,
   UAEndpointDescriptor^ endpointDescriptor,
   UANodeDescriptor^ nodeDescriptor,
   int samplingInterval
)

Parameters

client
The client object that will perform the operation.
endpointDescriptor
Endpoint descriptor. Identifies the OPC-UA server.
nodeDescriptor
Node descriptor. Identifies the node in OPC server's address space.
samplingInterval
The sampling interval (in milliseconds) indicates the fastest rate at which the Server should sample its underlying source for data changes.

Return Value

The method returns an integer handle that uniquely identifies the monitored item subscription.
Exceptions
ExceptionDescription
System.ArgumentNullException

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

System.ArgumentOutOfRangeException

The value of an argument is outside the allowable range of values as defined by the invoked method.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

Remarks

You can obtain nodeDescriptor e.g. by calling one of the browsing methods on EasyUAClientCore object.

 

This method operates (at least in part) asynchronously, with respect to the caller. The actual execution of the operation may be delayed, and the outcome of the operation (if any) is provided to the calling code using an event notification, callback, or other means explained in the text. In a properly written program, this method does not throw any exceptions. You should therefore not put try/catch statements or similar constructs around calls to this method. The only exceptions thrown by this method are for usage errors, i.e. when your code violates the usage contract of the method, such as passing in invalid arguments or calling the method when the state of the object does not allow it. Any operation-related errors (i.e. errors that depend on external conditions that your code cannot reliably check) are indicated by the means the operation returns its outcome (if any), which is described in the text. For more information, see Do not catch any exceptions with asynchronous or multiple-operation methods.
Example

.NET

.NET

COM

// This example shows how to subscribe to changes of a single monitored item and display the value of the item with each
// change.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeDataChange
    {
        public static void Overload1()
        {
            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;

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

            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(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 single monitored item and display the value of the item with 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 "../../../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..."
$client.SubscribeDataChange($endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

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 single monitored item and display the value of the item with each
# change.

# 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...')
IEasyUAClientExtension.SubscribeDataChange(client,
    endpointDescriptor,
    UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'),
    1000)

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 single monitored item and display the value of the item with each change.

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

Namespace _EasyUAClient
    Friend Class SubscribeDataChange
        Public Shared Sub Overload1()

            ' 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

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

            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(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

// Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

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

namespace UADocExamples.ComplexData._EasyUAClient
{
    class SubscribeDataChange
    {
        public static void Main1()
        {
            // Define which server and node we will work with.
            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/"
            UANodeDescriptor nodeDescriptor =
                "nsu=http://test.org/UA/Data/ ;i=10867"; // [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

            // Instantiate the client object and hook the event handler.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification;

            // Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just 
            // the data returned is different.
            Console.WriteLine("Subscribing...");
            client.SubscribeDataChange(endpointDescriptor, nodeDescriptor, samplingInterval:1000);

            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);

            // Unhook the event handler.
            client.DataChangeNotification -= client_DataChangeNotification;


            // Example output:
            //
            //Subscribing...
            //Processing data change events for 20 seconds...
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //Unsubscribing...
            //Waiting for 5 seconds...
        }

        static void client_DataChangeNotification(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value
            if (e.Succeeded)
                Console.WriteLine("Value: {0}", e.AttributeData.Value);
            else
                Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief);

            // For processing the internals of the data, refer to examples for GenericData and DataType classes.
        }
    }
}
# Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

# 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='')
    #
    # For processing the internals of the data, refer to examples for GenericData and DataType classes.


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/'

# [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue
nodeDescriptor = UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10867')

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

# Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just
# the data returned is different.
print('Subscribing...')
IEasyUAClientExtension.SubscribeDataChange(client,
    endpointDescriptor,
    nodeDescriptor,
    1000)   # samplingInterval

print('Processing data change events for 30 seconds...')
time.sleep(30)

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

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

# Unhook the event handler.
client.DataChangeNotification -= dataChangeNotification

print('Finished.')

' Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

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

Namespace ComplexData._EasyUAClient

    Friend Class SubscribeDataChange

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

            ' Define which node we will work with.
            Dim nodeDescriptor As UANodeDescriptor = _
                "nsu=http://test.org/UA/Data/ ;i=10867"  ' [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

            ' Instantiate the client object and hook the event handler.
            Dim client = New EasyUAClient
            AddHandler client.DataChangeNotification, AddressOf client_DataChangeNotification

            ' Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just 
            ' the data returned is different.
            Console.WriteLine("Subscribing...")
            client.SubscribeDataChange(endpointDescriptor, nodeDescriptor, samplingInterval:=1000)

            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))

            ' Unhook the event handler.
            RemoveHandler client.DataChangeNotification, AddressOf client_DataChangeNotification


            ' Example output:
            '
            'Subscribing...
            'Processing data change events for 20 seconds...
            '(ScalarValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ScalarValueDataType) structured
            '(ScalarValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ScalarValueDataType) structured
            '(ArrayValueDataType) structured
            '(ArrayValueDataType) structured
            '(ScalarValueDataType) structured
            '(ScalarValueDataType) structured
            '(ScalarValueDataType) structured
            'Unsubscribing...
            'Waiting for 5 seconds...
        End Sub

        Private Shared Sub client_DataChangeNotification(sender As Object, 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

            ' For processing the internals of the data, refer to examples for GenericData and DataType classes.
        End Sub
    End Class
End Namespace

// Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

type
  TClientEventHandlers33 = class
    procedure OnDataChangeNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUADataChangeNotificationEventArgs);
  end;

procedure TClientEventHandlers33.OnDataChangeNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUADataChangeNotificationEventArgs);
begin
  // Display value
  if eventArgs.Succeeded then
      WriteLn('Value: ', eventArgs.AttributeData.Value.ToString)
  else
      WriteLn('*** Failure: ', eventArgs.ErrorMessageBrief);

  // For processing the internals of the data, refer to examples for GenericData and DataType classes.
end;

class procedure SubscribeDataChange.Main;
var
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers33;
  EndpointDescriptor: string;
  NodeDescriptor: string;
begin
  // Define which server and node we will work with.
  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';
  NodeDescriptor := 'nsu=http://test.org/UA/Data/ ;i=10867';  // [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers33.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.OnDataChangeNotification;

  // Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just
  // the data returned is different.
  WriteLn('Subscribing...');
  Client.SubscribeDataChange(EndpointDescriptor, NodeDescriptor, 1000);

  WriteLn('Processing data change events for 20 seconds...');
  PumpSleep(20*1000);

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

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

  WriteLn('Finished.');
  FreeAndNil(Client);
  FreeAndNil(ClientEventHandlers);

  // Example output:
  //
  //Subscribing...
  //Processing data change events for 20 seconds...
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //Unsubscribing...
  //Waiting for 5 seconds...
end;
// Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

class ClientEvents {
    function DataChangeNotification($Sender, $E)
    {
        // Display value
        if ($E->Succeeded)
        printf("Value: %s\n", $E->AttributeData->Value);
        else
        printf("*** Failure : %s\n", $E->ErrorMessageBrief);
        // For processing the internals of the data, refer to examples for GenericData and DataType classes.
    }
}

// Define which server and node we will work with.
$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";
$NodeDescriptor = "nsu=http://test.org/UA/Data/ ;i=10867";  // [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

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

// Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just
// the data returned is different.
printf("Subscribing...\n");
$Client->SubscribeDataChange($EndpointDescriptor, $NodeDescriptor, 1000);

printf("Processing data change 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);
Requirements

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

See Also

Reference

IEasyUAClientExtension Class
IEasyUAClientExtension Members
Overload List

 

 

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