OPC Studio User's Guide and Reference
UnsubscribeItem Method (IEasyDAClientExtension)
Example 



OpcLabs.EasyOpcClassicCore Assembly > OpcLabs.EasyOpc.DataAccess Namespace > IEasyDAClientExtension Class : UnsubscribeItem Method
The client object that will perform the operation.
Item subscription handle as returned by the SubscribeItem method

Unsubscribe from changes of a particular OPC item.

Unsubscribe from OPC item, specifying its handle.

Syntax
'Declaration
 
<ExtensionAttribute()>
Public Shared Sub UnsubscribeItem( _
   ByVal client As IEasyDAClient, _
   ByVal handle As Integer _
) 
'Usage
 
Dim client As IEasyDAClient
Dim handle As Integer
 
IEasyDAClientExtension.UnsubscribeItem(client, handle)
[Extension()]
public static void UnsubscribeItem( 
   IEasyDAClient client,
   int handle
)
[Extension()]
public:
static void UnsubscribeItem( 
   IEasyDAClient^ client,
   int handle
) 

Parameters

client
The client object that will perform the operation.
handle
Item subscription handle as returned by the SubscribeItem method
Exceptions
ExceptionDescription

One of the arguments provided to a method is not valid.

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.

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 unsubscribe from multiple items using UnsubscribeMultipleItems method.

The item subscription handle becomes invalid after this method is called.

Example

.NET

// This example shows how subscribe to changes of multiple items, and unsubscribe from one of them.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using System.Threading;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    class UnsubscribeItem
    {
        public static void Main1()
        {
            // Instantiate the client object.
            using (var client = new EasyDAClient())
            {
                client.ItemChanged += client_ItemChanged;

                int[] handleArray = client.SubscribeMultipleItems(
                    new[] {
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, null), 
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000, null), 
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, null),  
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 1000, null)
                        });

                Console.WriteLine("Processing item changed events for 30 seconds...");
                Thread.Sleep(30 * 1000);

                Console.WriteLine("Unsubscribing from the first item...");
                client.UnsubscribeItem(handleArray[0]);

                Console.WriteLine();

                Console.WriteLine("Processing item changed events for 30 seconds...");
                Thread.Sleep(30 * 1000);
            }
        }

        // Item changed event handler
        static void client_ItemChanged(object sender, EasyDAItemChangedEventArgs e)
        {
            if (e.Succeeded)
                Console.WriteLine("{0}: {1}", e.Arguments.ItemDescriptor.ItemId, e.Vtq);
            else
                Console.WriteLine("{0} *** Failure: {1}", e.Arguments.ItemDescriptor.ItemId, e.ErrorMessageBrief);
        }
    }
}
# This example shows how subscribe to changes of multiple items, and unsubscribe from one of them.
#
# 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 .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

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


# Item changed event handler.
def itemChanged(sender, e):
    if e.Succeeded:
        print(e.Arguments.ItemDescriptor.ItemId, ': ', e.Vtq, sep='')
    else:
        print(e.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', e.ErrorMessageBrief, sep='')


# Instantiate the client object.
client = EasyDAClient()

client.ItemChanged += itemChanged

print('Subscribing item changes...')
handleArray = client.SubscribeMultipleItems([
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Trends.Ramp (1 min)', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Trends.Sine (1 min)', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Simulation.Register_I4', 1000, None),
    ])

for i in range(len(handleArray)):
    print('handleArray[', i, ']: ', handleArray[i], sep='')

print('Processing item change notifications for 30 seconds...')
time.sleep(30)

print('Unsubscribing from the first item...')
IEasyDAClientExtension.UnsubscribeItem(client, handleArray[0])

print('Processing item change notifications for 30 seconds...')
time.sleep(30)

client.ItemChanged -= itemChanged

print('Finished.')
' This example shows how subscribe to changes of multiple items, and unsubscribe from one of them.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports System.Threading
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class UnsubscribeItem
        Shared Sub Main1()
            Using client = New EasyDAClient()
                AddHandler client.ItemChanged, AddressOf client_ItemChanged

                Dim handleArray = client.SubscribeMultipleItems(
                        New DAItemGroupArguments() _
                        { _
                            New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, Nothing),
                            New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000, Nothing),
                            New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, Nothing),
                            New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 1000, Nothing)
                        })

                Console.WriteLine("Processing item changed events for 30 seconds...")
                Thread.Sleep(30 * 1000)

                Console.WriteLine("Unsubscribing from the first item...")
                client.UnsubscribeItem(handleArray(0))

                Console.WriteLine()

                Console.WriteLine("Processing item changed events for 30 seconds...")
                Thread.Sleep(30 * 1000)
            End Using
        End Sub

        ' Item changed event handler
        Private Shared Sub client_ItemChanged(sender As Object, e As EasyDAItemChangedEventArgs)
            If e.Succeeded Then
                Console.WriteLine("{0}: {1}", e.Arguments.ItemDescriptor.ItemId, e.Vtq)
            Else
                Console.WriteLine("{0} *** Failure: {1}", e.Arguments.ItemDescriptor.ItemId, e.ErrorMessageBrief)
            End If
        End Sub
    End Class
End Namespace
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