OPC Studio User's Guide and Reference
ChangeEventSubscription Method (EasyAEClientCore)
Example 



OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.AlarmsAndEvents Namespace > EasyAEClientCore Class : ChangeEventSubscription Method
Event subscription handle as returned by the SubscribeEvents method
The requested notification rate. The notification rate is in milliseconds and tells the server how often to send event notifications. This is a minimum time - do not send event notifications any faster that this UNLESS the buffer size is reached. A value of 0 for notification rate means that the server should send event notifications as soon as it gets them. This parameter is used to improve communications efficiency between client and server. This parameter is a recommendation from the client, and the server is allowed to ignore the parameter.
An AESubscriptionFilter that determines the filtering criteria to be used for the event subscription.

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

Activates or deactivates the subscription. If the client deactivates the subscription, then the server will no longer send event notifications to the client based on that subscription, and has no responsibility to buffer or maintain the event notifications. Thus, event notifications may be lost. Even if the subscription is inactive, the Refresh method will still function. In effect, this allows a client to obtain current condition states from time to time (by invoking Refresh) without the need to process event notifications in "real time".

Changes parameters of a particular event subscription.

Changes parameters of an event subscription. Specify new notification rate, subscription filter object, and an "active" flag.

Syntax
'Declaration
 
Public Sub ChangeEventSubscription( _
   ByVal handle As Integer, _
   ByVal notificationRate As Integer, _
   ByVal filter As AESubscriptionFilter, _
   ByVal active As Boolean _
) 
'Usage
 
Dim instance As EasyAEClientCore
Dim handle As Integer
Dim notificationRate As Integer
Dim filter As AESubscriptionFilter
Dim active As Boolean
 
instance.ChangeEventSubscription(handle, notificationRate, filter, active)
public void ChangeEventSubscription( 
   int handle,
   int notificationRate,
   AESubscriptionFilter filter,
   bool active
)
public:
void ChangeEventSubscription( 
   int handle,
   int notificationRate,
   AESubscriptionFilter^ filter,
   bool active
) 

Parameters

handle
Event subscription handle as returned by the SubscribeEvents method
notificationRate
The requested notification rate. The notification rate is in milliseconds and tells the server how often to send event notifications. This is a minimum time - do not send event notifications any faster that this UNLESS the buffer size is reached. A value of 0 for notification rate means that the server should send event notifications as soon as it gets them. This parameter is used to improve communications efficiency between client and server. This parameter is a recommendation from the client, and the server is allowed to ignore the parameter.
filter
An AESubscriptionFilter that determines the filtering criteria to be used for the event subscription.

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

active
Activates or deactivates the subscription. If the client deactivates the subscription, then the server will no longer send event notifications to the client based on that subscription, and has no responsibility to buffer or maintain the event notifications. Thus, event notifications may be lost. Even if the subscription is inactive, the Refresh method will still function. In effect, this allows a client to obtain current condition states from time to time (by invoking Refresh) without the need to process event notifications in "real time".
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

The user-defined state, as given when subscribing to the events, cannot be changed.

When you use this method, the OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel.EasyAENotificationEventArgs.Arguments in the event notifications and callbacks may, during the transition period, correspond to an improper (older or newer) value.

Example
// This example shows how to subscribe to events and later change the notification rate.
//
// 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 System.Threading;
using OpcLabs.EasyOpc.AlarmsAndEvents;
using OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel;

namespace DocExamples.AlarmsAndEvents._EasyAEClient
{
    class ChangeEventSubscription
    {
        public static void Main1()
        {
            // Instantiate the client object.
            using (var client = new EasyAEClient())
            {
                var eventHandler = new EasyAENotificationEventHandler(client_Notification);
                client.Notification += eventHandler;

                Console.WriteLine("Subscribing...");
                int handle = client.SubscribeEvents("", "OPCLabs.KitEventServer.2", 500);

                Console.WriteLine("Waiting for 10 seconds...");
                Thread.Sleep(10 * 1000);

                Console.WriteLine("Changing subscription...");
                client.ChangeEventSubscription(handle, 5 * 1000);

                Console.WriteLine("Waiting for 50 seconds...");
                Thread.Sleep(50 * 1000);

                client.UnsubscribeEvents(handle);
            }
        }

        // Notification event handler
        static void client_Notification(object sender, EasyAENotificationEventArgs e)
        {
            if (!e.Succeeded)
            {
                Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief);
                return;
            }

            if (!(e.EventData is null))
                Console.WriteLine(e.EventData.Message);
        }
    }
}
' This example shows how to subscribe to events and later change the notification rate.
'
' 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 System.Threading
Imports OpcLabs.EasyOpc.AlarmsAndEvents
Imports OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel

Namespace AlarmsAndEvents._EasyAEClient

    Friend Class ChangeEventSubscription
        Public Shared Sub Main1()
            Using client = New EasyAEClient()
                Dim eventHandler = New EasyAENotificationEventHandler(AddressOf client_Notification)
                AddHandler client.Notification, eventHandler

                Console.WriteLine("Subscribing...")
                Dim handle As Integer = client.SubscribeEvents("", "OPCLabs.KitEventServer.2", 500)

                Console.WriteLine("Waiting for 10 seconds...")
                Thread.Sleep(10 * 1000)

                Console.WriteLine("Changing subscription...")
                client.ChangeEventSubscription(handle, 5 * 1000)

                Console.WriteLine("Waiting for 50 seconds...")
                Thread.Sleep(50 * 1000)

                client.UnsubscribeEvents(handle)
            End Using
        End Sub

        ' Notification event handler
        Private Shared Sub client_Notification(ByVal sender As Object, ByVal e As EasyAENotificationEventArgs)
            If Not e.Succeeded Then
                Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief)
                Exit Sub
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine(e.EventData.Message)
            End If
        End Sub
    End Class
End Namespace
# This example shows how to subscribe to events and later change the notification rate.
#
# 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 import *
from OpcLabs.EasyOpc.AlarmsAndEvents import *


# Notification event handler
def notification(sender, e):
    if not e.Succeeded:
        print('*** Failure: ', e.ErrorMessageBrief, sep='')
        return
    else:
        if e.EventData is not None:
            print(e.EventData.Message)


# Instantiate the client object
client = EasyAEClient()

client.Notification += notification

print('Subscribing events...')
handle = IEasyAEClientExtension.SubscribeEvents(client, '', 'OPCLabs.KitEventServer.2', 500)

print('Waiting for 10 seconds...')
time.sleep(10)

print('Changing event subscription...')
IEasyAEClientExtension.ChangeEventSubscription(client, handle, 5*1000)

print('Waiting for 50 seconds...')
time.sleep(50)

print('Unsubscribing events...')
client.UnsubscribeAllEvents()

client.Notification -= notification

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

See Also