OPC Studio User's Guide and Reference
SubscribeEvents(IEasyAEClient,String,String,Int32) Method
Example 



OpcLabs.EasyOpcClassicCore Assembly > OpcLabs.EasyOpc.AlarmsAndEvents Namespace > IEasyAEClientExtension Class > SubscribeEvents Method : SubscribeEvents(IEasyAEClient,String,String,Int32) 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).

Name of the machine. Determines the computer on which the OPC server is located. It may be an empty string, in which case the OPC server is assumed to exist on the local computer or at the computer specified for it by DCOM configuration.

The value represents a UNC or DNS computer name. Any string can be passed to this parameter (i.e. will not cause System.ArgumentException), but not all values make sense and will work when an operation using them is attempted. IPv6 addresses are normally enclosed between '[' and ']'.

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

Contains ProgID of the OPC server.

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

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.
Subscribe to OPC events. Specify machine name, server class, and notification rate. The subscription is created active, and it will automatically perform a Refresh after each successful connection to the server. No event attributes will be returned with the notifications, and events will not be filtered. Does not pass in a "state" object for use in event notifications.
Syntax
'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function SubscribeEvents( _
   ByVal client As IEasyAEClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal notificationRate As Integer _
) As Integer
'Usage
 
Dim client As IEasyAEClient
Dim machineName As String
Dim serverClass As String
Dim notificationRate As Integer
Dim value As Integer
 
value = IEasyAEClientExtension.SubscribeEvents(client, machineName, serverClass, notificationRate)

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).

machineName
Name of the machine. Determines the computer on which the OPC server is located. It may be an empty string, in which case the OPC server is assumed to exist on the local computer or at the computer specified for it by DCOM configuration.

The value represents a UNC or DNS computer name. Any string can be passed to this parameter (i.e. will not cause System.ArgumentException), but not all values make sense and will work when an operation using them is attempted. IPv6 addresses are normally enclosed between '[' and ']'.

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

serverClass
Contains ProgID of the OPC server.

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

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.

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.

The value of an argument is outside the allowable range of values as defined by the invoked method.

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.

 

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 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 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 PowerShell on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-PowerShell .
# 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.

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.AlarmsAndEvents

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"

# Instantiate the client object.
$client = New-Object EasyAEClient

# Notification event handler
Register-ObjectEvent -InputObject $client -EventName Notification -Action { 
    if (-not $EventArgs.Succeeded) {
        Write-Host "*** Failure: $($EventArgs.ErrorMessageBrief)"
        #return
    }
    if ($EventArgs.EventData -ne $null) {
        Write-Host $EventArgs.EventData.Message
    }
}

Write-Host "Subscribing events..."
$handle = [IEasyAEClientExtension]::SubscribeEvents($client, "", "OPCLabs.KitEventServer.2", 1000)

Write-Host "Processing event notifications for 1 minute..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 60) {    
    Start-Sleep -Seconds 1
}

Write-Host "Unsubscribing events..."
$client.UnsubscribeEvents($handle)

Write-Host "Finished."
' 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 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
    Partial Friend Class SubscribeEvents
        Public Shared Sub Main1()
            Using client = New EasyAEClient()
                Dim eventHandler = New EasyAENotificationEventHandler(AddressOf client_Notification)
                AddHandler client.Notification, eventHandler

                Dim handle As Integer = client.SubscribeEvents("", "OPCLabs.KitEventServer.2", 1000)

                Console.WriteLine("Processing event notifications for 1 minute...")
                Thread.Sleep(60 * 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 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 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', 1000)

print('Processing event notifications for 1 minute...')
time.sleep(60)

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

client.Notification -= notification

print('Finished.')
// This example shows how to work with Software Tolbox TOP Server 5 Alarms and Events.
// Use simdemo_WithA&E.opf configuration file and write a value above 1000 to Channel1.Device1.Tag1 or Channel1.Device1.Tag2.
//
// 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.Diagnostics;
using System.Threading;
using OpcLabs.EasyOpc.AlarmsAndEvents;
using OpcLabs.EasyOpc.AlarmsAndEvents.AddressSpace;
using OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.AlarmsAndEvents.SWToolbox
{
    class TOPServer_AE
    {
        public static void Main1()
        {
            // Instantiate the client object.
            var client = new EasyAEClient();

            // Browse for some areas and sources

            AENodeElementCollection areaElements;
            try
            {
                areaElements = client.BrowseAreas("", "SWToolbox.TOPServer_AE.V5", "");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            foreach (AENodeElement areaElement in areaElements)
            {
                Debug.Assert(!(areaElement is null));
                Debug.Assert(!(areaElement.QualifiedName is null));

                Console.WriteLine("areaElements[\"{0}\"]:", areaElement.Name);
                Console.WriteLine("    .QualifiedName: {0}", areaElement.QualifiedName);

                AENodeElementCollection sourceElements =
                    client.BrowseSources("", "SWToolbox.TOPServer_AE.V5", areaElement.QualifiedName);
                foreach (AENodeElement sourceElement in sourceElements)
                {
                    Debug.Assert(sourceElement != null);

                    Console.WriteLine("    sourceElements[\"{0}\"]:", sourceElement.Name);
                    Console.WriteLine("        .QualifiedName: {0}", sourceElement.QualifiedName);
                }
            }

            // Query for event categories

            AECategoryElementCollection categoryElements;
            try
            {
                categoryElements = client.QueryEventCategories("", "SWToolbox.TOPServer_AE.V5");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            foreach (AECategoryElement categoryElement in categoryElements)
            {
                Debug.Assert(categoryElement != null);
                Console.WriteLine("CategoryElements[\"{0}\"].Description: {1}", categoryElement.CategoryId,
                                  categoryElement.Description);
            }

            // Subscribe to events, wait, and unsubscribe

            var eventHandler = new EasyAENotificationEventHandler(client_Notification);
            client.Notification += eventHandler;

            int handle = client.SubscribeEvents("", "SWToolbox.TOPServer_AE.V5", 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.Exception is null)) Console.WriteLine("e.Exception.Message: {0}", e.Exception.Message);
            if (!(e.Exception is null)) Console.WriteLine("e.Exception.Source: {0}", e.Exception.Source);
            Console.WriteLine("e.Refresh: {0}", e.Refresh);
            Console.WriteLine("e.RefreshComplete: {0}", e.RefreshComplete);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.QualifiedSourceName: {0}", e.EventData.QualifiedSourceName);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Time: {0}", e.EventData.Time);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Message: {0}", e.EventData.Message);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.EventType: {0}", e.EventData.EventType);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.CategoryId: {0}", e.EventData.CategoryId);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Severity: {0}", e.EventData.Severity);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.ConditionName: {0}", e.EventData.ConditionName);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.SubconditionName: {0}", e.EventData.SubconditionName);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Enabled: {0}", e.EventData.Enabled);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Active: {0}", e.EventData.Active);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Acknowledged: {0}", e.EventData.Acknowledged);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.Quality: {0}", e.EventData.Quality);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.AcknowledgeRequired: {0}", e.EventData.AcknowledgeRequired);
            if (!(e.EventData is null)) Console.WriteLine("e.EventData.ActiveTime: {0}", e.EventData.ActiveTime);
        }
    }
}
' This example shows how to work with Software Tolbox TOP Server 5 Alarms and Events.
' Use simdemo_WithA&E.opf configuration file and write a value above 1000 to Channel1.Device1.Tag1 or Channel1.Device1.Tag2.
'
' 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.AddressSpace
Imports OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel
Imports OpcLabs.EasyOpc.OperationModel

Namespace AlarmsAndEvents.SWToolbox

    Friend Class TOPServer_AE
        Public Shared Sub Main1()
            Dim client = New EasyAEClient()

            ' Browse for some areas and sources

            Dim areaElements As AENodeElementCollection
            Try
                areaElements = client.BrowseAreas("", "SWToolbox.TOPServer_AE.V5", "")
            Catch opcException As OpcException
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
                Exit Sub
            End Try

            For Each areaElement As AENodeElement In areaElements
                Debug.Assert(areaElement IsNot Nothing)
                Debug.Assert(areaElement.QualifiedName IsNot Nothing)

                Console.WriteLine("areaElements[""{0}""]:", areaElement.Name)
                Console.WriteLine("    .QualifiedName: {0}", areaElement.QualifiedName)

                Dim sourceElements As AENodeElementCollection = client.BrowseSources("", "SWToolbox.TOPServer_AE.V5", areaElement.QualifiedName)
                For Each sourceElement As AENodeElement In sourceElements
                    Debug.Assert(sourceElement IsNot Nothing)

                    Console.WriteLine("    sourceElements[""{0}""]:", sourceElement.Name)
                    Console.WriteLine("        .QualifiedName: {0}", sourceElement.QualifiedName)
                Next sourceElement
            Next areaElement

            ' Query for event categories

            Dim categoryElements As AECategoryElementCollection
            Try
                categoryElements = client.QueryEventCategories("", "SWToolbox.TOPServer_AE.V5")
            Catch opcException As OpcException
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
                Exit Sub
            End Try

            For Each categoryElement As AECategoryElement In categoryElements
                Debug.Assert(categoryElement IsNot Nothing)
                Console.WriteLine("CategoryElements[""{0}""].Description: {1}", categoryElement.CategoryId, categoryElement.Description)
            Next categoryElement

            ' Subscribe to events, wait, and unsubscribe

            Dim eventHandler = New EasyAENotificationEventHandler(AddressOf client_Notification)
            AddHandler client.Notification, eventHandler

            Dim handle As Integer = client.SubscribeEvents("", "SWToolbox.TOPServer_AE.V5", 1000)

            Console.WriteLine("Processing event notifications for 1 minute...")
            Thread.Sleep(60 * 1000)

            client.UnsubscribeEvents(handle)
        End Sub

        ' Notification event handler
        Private Shared Sub client_Notification(ByVal sender As Object, ByVal e As EasyAENotificationEventArgs)
            If e.Exception IsNot Nothing Then
                Console.WriteLine("e.Exception.Message: {0}", e.Exception.Message)
            End If
            If e.Exception IsNot Nothing Then
                Console.WriteLine("e.Exception.Source: {0}", e.Exception.Source)
            End If
            Console.WriteLine("e.Refresh: {0}", e.Refresh)
            Console.WriteLine("e.RefreshComplete: {0}", e.RefreshComplete)
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.QualifiedSourceName: {0}", e.EventData.QualifiedSourceName)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Time: {0}", e.EventData.Time)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Message: {0}", e.EventData.Message)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.EventType: {0}", e.EventData.EventType)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.CategoryId: {0}", e.EventData.CategoryId)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Severity: {0}", e.EventData.Severity)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.ConditionName: {0}", e.EventData.ConditionName)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.SubconditionName: {0}", e.EventData.SubconditionName)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Enabled: {0}", e.EventData.Enabled)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Active: {0}", e.EventData.Active)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Acknowledged: {0}", e.EventData.Acknowledged)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.Quality: {0}", e.EventData.Quality)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.AcknowledgeRequired: {0}", e.EventData.AcknowledgeRequired)
            End If
            If e.EventData IsNot Nothing Then
                Console.WriteLine("e.EventData.ActiveTime: {0}", e.EventData.ActiveTime)
            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