SubscribeMonitoredItem(IEasyUAClient,UAMonitoredItemArguments,EasyUADataChangeNotificationEventHandler) Method

Subscribe to a monitored item, specifying an object that holds all necessary arguments, and a data change callback method.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function SubscribeMonitoredItem( _
   ByVal client As IEasyUAClient, _
   ByVal monitoredItemArguments As UAMonitoredItemArguments, _
   ByVal dataChangeCallback As EasyUADataChangeNotificationEventHandler _
) As Integer

'Usage
 
Dim client As IEasyUAClient
Dim monitoredItemArguments As UAMonitoredItemArguments
Dim dataChangeCallback As EasyUADataChangeNotificationEventHandler
Dim value As Integer
 
value = IEasyUAClientExtension.SubscribeMonitoredItem(client, monitoredItemArguments, dataChangeCallback)

[Extension()]
public static int SubscribeMonitoredItem( 
   IEasyUAClient client,
   UAMonitoredItemArguments monitoredItemArguments,
   EasyUADataChangeNotificationEventHandler dataChangeCallback
)

[Extension()]
public:
static int SubscribeMonitoredItem( 
   IEasyUAClient^ client,
   UAMonitoredItemArguments^ monitoredItemArguments,
   EasyUADataChangeNotificationEventHandler^ dataChangeCallback
)

Parameters

client

The client object that will perform the operation.

This is typically the EasyUAClient object.

The value of this parameter cannot be null (Nothing in Visual Basic).

monitoredItemArguments

Array of arguments, one element per each monitored item involved in the operation.

The value of this parameter cannot be null (Nothing in Visual Basic).

dataChangeCallback

A callback method to be invoked for each significant monitored item change.

The value of this parameter cannot be null (Nothing in Visual Basic).

Return Value

The method returns an integer handle that uniquely identifies the monitored item subscription.

Exceptions

Exception Description

Exception	Description
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.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.

Remarks

This is an extension method (info: C#, VB.NET). In languages that have support for extensions methods (such as C# and VB.NET), you can use the extension method as if it were a regular method on the object that is its first parameter. In other languages (such as with Python.NET), you will call the extension as a static method, and pass it the object on which it acts as its first parameter.

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

CSharp
VB.NET
Python

// This example shows how to subscribe to range of values from an array.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

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

namespace UACommonDocExamples._UAIndexRangeList
{
    partial class Usage
    {
        public static void Subscribe()
        {
            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
            var client = new EasyUAClient();

            Console.WriteLine("Subscribing to range...");
            var attributeArguments = new UAAttributeArguments(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10933")
                {
                    IndexRangeList = UAIndexRangeList.OneDimension(2, 4)
                };
            var monitoredItemArguments = new UAMonitoredItemArguments(attributeArguments, monitoringParameters:1000);
            // The callback is a lambda expression the displays the value
            client.SubscribeMonitoredItem(monitoredItemArguments,
                (sender, eventArgs) =>
                {
                    if (eventArgs.Succeeded)
                    {
                        var arrayValue = eventArgs.AttributeData.Value as Int32[];
                        if (!(arrayValue is null))
                            Console.WriteLine($"Value: {{{String.Join(",", arrayValue)}}}");
                    }
                    else
                        Console.WriteLine($"*** Failure: {eventArgs.ErrorMessageBrief}");
                });

            Console.WriteLine("Processing data change events for 10 seconds...");
            System.Threading.Thread.Sleep(10 * 1000);

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

            Console.WriteLine("Waiting for 2 seconds...");
            System.Threading.Thread.Sleep(2 * 1000);
        }
    }
}

' This example shows how to subscribe to range of values from an array.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.

Imports Opc.Ua
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _UAIndexRangeList
    Partial Friend Class Usage
        Public Shared Sub Subscribe()

            ' 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
            Dim client = New EasyUAClient()

            Console.WriteLine("Subscribing to range...")
            Dim attributeArguments = New UAAttributeArguments(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10933") With
                {
                    .IndexRangeList = UAIndexRangeList.OneDimension(2, 4)
                }
            Dim monitoredItemArguments = New UAMonitoredItemArguments(attributeArguments, monitoringParameters:=1000)
            ' The callback is a lambda expression the displays the value
            client.SubscribeMonitoredItem(monitoredItemArguments,
                Sub(sender, eventArgs)
                    If eventArgs.Succeeded Then
                        Dim arrayValue = CType(eventArgs.AttributeData.Value, Int32())
                        If (arrayValue IsNot Nothing) Then
                            Console.WriteLine($"Value: {{{String.Join(",", arrayValue)}}}")
                        End If
                    Else
                        Console.WriteLine("*** Failure: {0}", eventArgs.ErrorMessageBrief)
                    End If
                End Sub)

            Console.WriteLine("Processing data change events for 10 seconds...")
            Threading.Thread.Sleep(10 * 1000)

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

            Console.WriteLine("Waiting for 2 seconds...")
            Threading.Thread.Sleep(2 * 1000)
        End Sub
    End Class
End Namespace

# This example shows how to subscribe to range of values from an array.
#
# 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 .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# 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, eventArgs):
    # Display value.
    if eventArgs.Succeeded:
        arrayValue = eventArgs.AttributeData.Value
        print('Value: {', ", ".join(["{}"]*len(arrayValue)).format(*arrayValue), '}', sep='')
    else:
        print('*** Failure: ', eventArgs.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.
client = EasyUAClient()

print('Subscribing to range...')
attributeArguments = UAAttributeArguments(endpointDescriptor, UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10933'))
attributeArguments.IndexRangeList = UAIndexRangeList.OneDimension(2, 4)
monitoredItemArguments = UAMonitoredItemArguments(attributeArguments, UAMonitoringParameters(1000))
IEasyUAClientExtension.SubscribeMonitoredItem(client,
    monitoredItemArguments,
    EasyUADataChangeNotificationEventHandler(dataChangeNotification))

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

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

print('Waiting for 2 seconds...')
time.sleep(2)

print('Finished.')

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

IEasyUAClientExtension Class
IEasyUAClientExtension Members
Overload List

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