ChangeEventSubscription Method (EasyAEClient)

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

public void ChangeEventSubscription( 
   int handle,
   int notificationRate,
   AESubscriptionFilter filter,
   bool active
)

public:
void ChangeEventSubscription( 
   int handle,
   int notificationRate,
   AESubscriptionFilter^ filter,
   bool active
)

'Declaration
 
Public Sub ChangeEventSubscription( _
   ByVal handle As Integer, _
   ByVal notificationRate As Integer, _
   ByVal filter As AESubscriptionFilter, _
   ByVal active As Boolean _
)

'Usage
 
Dim instance As EasyAEClient
Dim handle As Integer
Dim notificationRate As Integer
Dim filter As AESubscriptionFilter
Dim active As Boolean
 
instance.ChangeEventSubscription(handle, notificationRate, filter, 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.
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

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.

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.

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

// This example shows how to subscribe to events and later change the notification rate.

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.

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

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2012 R2, Windows Server 2016; .NET: Linux, macOS, Microsoft Windows

Reference

EasyAEClient Class
EasyAEClient Members

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