OPC Studio User's Guide and Reference
SubscribeEvents(IEasyAEClient,AEEventsSubscriptionArguments,EasyAENotificationEventHandler) Method
Example 



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OpcLabs.EasyOpcClassicCore Assembly > OpcLabs.EasyOpc.AlarmsAndEvents Namespace > IEasyAEClientExtension Class > SubscribeEvents Method : SubscribeEvents(IEasyAEClient,AEEventsSubscriptionArguments,EasyAENotificationEventHandler) Method
The client object that will perform the operation.

This is typically the EasyAEClient object.

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

Holds an OPC server descriptor, event subscription parameters, and possibly a callback method, as arguments to subscription operation.

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

A callback method to be invoked for each event notification.

The value of this parameter can be null (Nothing in Visual Basic).

Subscribe to OPC events, using an object that holds all necessary arguments, and an optional callback.
Syntax
'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function SubscribeEvents( _
   ByVal client As IEasyAEClient, _
   ByVal arguments As AEEventsSubscriptionArguments, _
   ByVal callback As EasyAENotificationEventHandler _
) As Integer
 
'Usage
 
Dim client As IEasyAEClient
Dim arguments As AEEventsSubscriptionArguments
Dim callback As EasyAENotificationEventHandler
Dim value As Integer
 
value = IEasyAEClientExtension.SubscribeEvents(client, arguments, callback)

Parameters

client
The client object that will perform the operation.

This is typically the EasyAEClient object.

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

arguments
Holds an OPC server descriptor, event subscription parameters, and possibly a callback method, as arguments to subscription operation.

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

callback
A callback method to be invoked for each event notification.

The value of this parameter can be null (Nothing in Visual Basic).

Return Value

The method returns an integer handle that uniquely identifies the event subscription.
Exceptions
ExceptionDescription

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.

Example
// This example shows how to subscribe to events and display the event message with each notification. It also shows how to 
// unsubscribe afterwards.
//
// 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
{
    partial class SubscribeEvents
    {
        public static void Main1()
        {
            // Instantiate the client object.
            using (var client = new EasyAEClient())
            {
                var eventHandler = new EasyAENotificationEventHandler(client_Notification);
                client.Notification += eventHandler;

                int handle = client.SubscribeEvents("", "OPCLabs.KitEventServer.2", 1000);

                Console.WriteLine("Processing event notifications for 1 minute...");
                Thread.Sleep(60 * 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 filter the events by their category.
//
// 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;
using OpcLabs.EasyOpc.DataAccess;

namespace DocExamples.AlarmsAndEvents._EasyAEClient
{
    partial class SubscribeEvents
    {
        // Instantiate the OPC-A&E client object.
        static readonly EasyAEClient AEClient = new EasyAEClient();

        // Instantiate the OPC-DA client object.
        static readonly EasyDAClient DAClient = new EasyDAClient();

        public static void FilterByCategories()
        {
            var eventHandler = new EasyAENotificationEventHandler(AEClient_Notification_FilterByCategories);
            AEClient.Notification += eventHandler;

            Console.WriteLine("Processing event notifications...");
            var subscriptionFilter = new AESubscriptionFilter
            {
                Categories = new long[] { 15531778 }
            };
            // You can also filter using event types, severity, areas, and sources.
            int handle = AEClient.SubscribeEvents("", "OPCLabs.KitEventServer.2", 1000, null, subscriptionFilter);

            // Allow time for initial refresh
            Thread.Sleep(5 * 1000);

            // Set some events to active state.
            DAClient.WriteItemValue("", "OPCLabs.KitServer.2", "SimulateEvents.ConditionState1.Activate", true);
            DAClient.WriteItemValue("", "OPCLabs.KitServer.2", "SimulateEvents.ConditionState2.Activate", true);

            Thread.Sleep(10 * 1000);

            AEClient.UnsubscribeEvents(handle);
            AEClient.Notification -= eventHandler;
        }

        // Notification event handler
        static void AEClient_Notification_FilterByCategories(object sender, EasyAENotificationEventArgs e)
        {
            Console.WriteLine();
            Console.WriteLine(e);
            if (!e.Succeeded)
                return;

            Console.WriteLine("Refresh: {0}", e.Refresh);
            Console.WriteLine("RefreshComplete: {0}", e.RefreshComplete);
            AEEventData eventData = e.EventData;
            if (!(eventData is null))
            {
                Console.WriteLine("Event.CategoryId: {0}", eventData.CategoryId);
                Console.WriteLine("Event.QualifiedSourceName: {0}", eventData.QualifiedSourceName);
                Console.WriteLine("Event.Message: {0}", eventData.Message);
                Console.WriteLine("Event.Active: {0}", eventData.Active);
                Console.WriteLine("Event.Acknowledged: {0}", eventData.Acknowledged);
            }
        }
    }
}
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