SubscribeMonitoredItem(IEasyUAClient,UAMonitoredItemArguments,EasyUADataChangeNotificationEventHandler) Method

Subscribe to changes of a particular monitored item. For each significant monitored item change, either the IEasyUAClient.DataChangeNotification event is generated, or a specified callback method is invoked. 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.
monitoredItemArguments: Array of arguments, one element per each monitored item involved in the operation.
dataChangeCallback: A callback method to be invoked for each significant monitored item change.

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

It is more efficient to subscribe to multiple monitored items using SubscribeMultipleMonitoredItems method.

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

// This example shows how to subscribe to range of values from an array.

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

namespace UADocExamples._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.

# 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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