SubscribeEvent(IEasyUAClient,UAEndpointDescriptor,UANodeDescriptor,Int32,EasyUAEventNotificationEventHandler) Method

Subscribe to an event. Specify an endpoint descriptor, node id, sampling interval, and a callback method.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function SubscribeEvent( _
   ByVal client As IEasyUAClient, _
   ByVal endpointDescriptor As UAEndpointDescriptor, _
   ByVal nodeDescriptor As UANodeDescriptor, _
   ByVal samplingInterval As Integer, _
   ByVal eventCallback As EasyUAEventNotificationEventHandler _
) As Integer

'Usage
 
Dim client As IEasyUAClient
Dim endpointDescriptor As UAEndpointDescriptor
Dim nodeDescriptor As UANodeDescriptor
Dim samplingInterval As Integer
Dim eventCallback As EasyUAEventNotificationEventHandler
Dim value As Integer
 
value = IEasyUAClientExtension.SubscribeEvent(client, endpointDescriptor, nodeDescriptor, samplingInterval, eventCallback)

[Extension()]
public static int SubscribeEvent( 
   IEasyUAClient client,
   UAEndpointDescriptor endpointDescriptor,
   UANodeDescriptor nodeDescriptor,
   int samplingInterval,
   EasyUAEventNotificationEventHandler eventCallback
)

[Extension()]
public:
static int SubscribeEvent( 
   IEasyUAClient^ client,
   UAEndpointDescriptor^ endpointDescriptor,
   UANodeDescriptor^ nodeDescriptor,
   int samplingInterval,
   EasyUAEventNotificationEventHandler^ eventCallback
)

Parameters

client: The client object that will perform the operation.
endpointDescriptor: Endpoint descriptor. Identifies the OPC-UA server.
nodeDescriptor: Node descriptor. Identifies the node in OPC server's address space.
samplingInterval: The sampling interval (in milliseconds) indicates the fastest rate at which the Server should sample its underlying source for events.
eventCallback: A callback method to be invoked for each significant monitored item change.

Return Value

The method returns an integer handle that uniquely identifies the monitored item subscription.

Exceptions

Exception Description

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. 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.
System.ArgumentOutOfRangeException	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.

System.ArgumentNullException

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.

System.ArgumentOutOfRangeException

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

If eventCallback is a null reference, only the IEasyUAClient.EventNotification event is generated, and no callback method is invoked.

You can obtain nodeDescriptor e.g. by calling one of the browsing methods on EasyUAClientCore object.

Selects all relevant fields of OpcLabs.EasyOpc.UA.AlarmsAndConditions.UABaseEventObject to be returned in event notifications.

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 event notifications and display each incoming event
// using a callback method that is provided as lambda expression.

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.AddressSpace.Standard;

namespace UADocExamples.AlarmsAndConditions
{
    partial class SubscribeEvent
    {
        public static void CallbackLambda()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";

            // Instantiate the client object
            var client = new EasyUAClient();

            Console.WriteLine("Subscribing...");
            // The callback is a lambda expression the displays the event
            client.SubscribeEvent(
                endpointDescriptor,
                UAObjectIds.Server,
                1000,
                (sender, eventArgs) => Console.WriteLine(eventArgs));
            // Remark: Production code needs to check eventArgs.Exception before accessing eventArgs.EventData.

            Console.WriteLine("Processing event notifications for 30 seconds...");
            System.Threading.Thread.Sleep(30 * 1000);

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();

            Console.WriteLine("Waiting for 2 seconds...");
            System.Threading.Thread.Sleep(2 * 1000);
        }
    }
}

# This example shows how to subscribe to event notifications and display each incoming event
# using a callback method that is provided as lambda expression.

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.AddressSpace.Standard import *


# Define which server we will work with.
endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer')

# Instantiate the client object.
client = EasyUAClient()

print('Subscribing...')
# The callback is a lambda expression the displays the event.
IEasyUAClientExtension.SubscribeEvent(
    client,
    endpointDescriptor,
    UANodeDescriptor(UAObjectIds.Server),
    1000,
    EasyUAEventNotificationEventHandler(lambda server, eventArgs: print(eventArgs)))
# Remark: Production code needs to check eventArgs.Exception before accessing eventArgs.EventData.

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

print('Unsubscribing...')
client.UnsubscribeAllMonitoredItems()

print('Waiting for 2 seconds...')
time.sleep(2)

print('Finished.')

' This example shows how to subscribe to event notifications and display each incoming event
' using a callback method that is provided as lambda expression.

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.AddressSpace.Standard

Namespace AlarmsAndConditions
    Partial Friend Class SubscribeEvent
        Public Shared Sub CallbackLambda()
            ' Instantiate the client object
            Dim client = New EasyUAClient()

            Console.WriteLine("Subscribing...")
            ' The callback is a lambda expression the displays the event
            client.SubscribeEvent( _
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer", _
                UAObjectIds.Server, _
                1000, _
                Sub(sender, eventArgs) Console.WriteLine(eventArgs))
            ' Remark: Production code would check e.Exception before accessing e.EventData.

            Console.WriteLine("Processing event notifications for 10 seconds...")
            Threading.Thread.Sleep(10 * 1000)

            Console.WriteLine("Unsubscribing...")
            client.UnsubscribeAllMonitoredItems()

            Console.WriteLine("Waiting for 2 seconds...")
            Threading.Thread.Sleep(2 * 1000)
        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

Reference

IEasyUAClientExtension Class
IEasyUAClientExtension Members
Overload List

Send Documentation Feedback. Resources: Knowledge Base. Technical support: Online Forums, FAQ.