OPC Studio User's Guide and Reference
ServerConditionChanged Event (IEasyUAClientConnectionMonitoring)
Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA.Services Namespace > IEasyUAClientConnectionMonitoring Interface : ServerConditionChanged Event
Raised for a change in the condition of an OPC server.
Syntax
'Declaration
 
Event ServerConditionChanged As EasyUAServerConditionChangedEventHandler
'Usage
 
Dim instance As IEasyUAClientConnectionMonitoring
Dim handler As EasyUAServerConditionChangedEventHandler
 
AddHandler instance.ServerConditionChanged, handler
event EasyUAServerConditionChangedEventHandler ServerConditionChanged
event EasyUAServerConditionChangedEventHandler^ ServerConditionChanged
Event Data

The event handler receives an argument of type EasyUAServerConditionChangedEventArgs containing data related to this event. The following EasyUAServerConditionChangedEventArgs properties provide information specific to this event.

PropertyDescription
Indicates whether the object is now connected. (Inherited from OpcLabs.BaseLib.Communication.ConnectedConditionChangedEventArgs)
Indicates the state of the connection. (Inherited from OpcLabs.BaseLib.Communication.ConnectedConditionChangedEventArgs)
Default endpoint descriptor.  
Diagnostics information (such as warnings) assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Count of diagnostic information elements assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Textual summary of diagnostics information, one message per line. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Contains the endpoint descriptor, i.e. the data defining a connection to the OPC-UA Server (mainly, its URL string).  
Gets or sets the error ID of the error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets or sets a message that describes the current exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
The first line of the error message. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets the current exception. Contains null reference when no exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
A normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Diagnostics collection. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
A normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Exception object, or null if there was no error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
When disconnected, time to next reconnection attempt. In milliseconds. (Inherited from OpcLabs.BaseLib.Communication.ConnectedConditionChangedEventArgs)
Gets or sets statistics for the connected condition at the moment the event was generated. (Inherited from OpcLabs.BaseLib.Communication.ConnectedConditionChangedEventArgs)
Status information corresponding to the contents of the event arguments. (Inherited from OpcLabs.BaseLib.Communication.ConnectedConditionChangedEventArgs)
Gets indication whether the operation has succeeded. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Example

.NET

// This example shows how to monitor connections to and disconnections from the OPC UA server.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using Microsoft.Extensions.DependencyInjection;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.OperationModel;
using OpcLabs.EasyOpc.UA.Services;

namespace UADocExamples._EasyUAClientConnectionMonitoring
{
    class ServerConditionChanged
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object.
            using (var client = new EasyUAClient())
            {
                // Obtain the client connection monitoring service.
                IEasyUAClientConnectionMonitoring clientConnectionMonitoring = client.GetService<IEasyUAClientConnectionMonitoring>();
                if (clientConnectionMonitoring is null)
                {
                    Console.WriteLine("The client connection monitoring service is not available.");
                    return;
                }

                // Hook events.
                client.DataChangeNotification += client_DataChangeNotification;
                clientConnectionMonitoring.ServerConditionChanged += clientConnectionMonitoring_OnServerConditionChanged;

                try
                {
                    Console.WriteLine("Reading (1)");
                    // The first read will cause a connection to the server.
                    UAAttributeData attributeData1 = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853");
                    Console.WriteLine(attributeData1);

                    Console.WriteLine("Reading (2)");
                    // The second read, because it closely follows the first one, will reuse the connection that is already
                    // open.
                    UAAttributeData attributeData2 = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853");
                    Console.WriteLine(attributeData2);
                }
                catch (UAException uaException)
                {
                    Console.WriteLine($"*** Failure: {uaException.GetBaseException().Message}");
                }

                Console.WriteLine("Waiting for 10 seconds...");
                // Since the connection is now not used for some time, it will be closed.
                System.Threading.Thread.Sleep(10 * 1000);

                Console.WriteLine("Subscribing...");
                // Subscribing to a monitored item will cause a connection to the server, if one is not yet open.
                client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000);

                Console.WriteLine("Waiting for 10 seconds...");
                // The connection will not be closed as long as there are any subscriptions to the server.
                System.Threading.Thread.Sleep(10 * 1000);

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

                Console.WriteLine("Waiting for 10 seconds...");
                // After some delay, the connection will be closed, because there are no subscriptions to the server.
                System.Threading.Thread.Sleep(10 * 1000);

                Console.WriteLine("Finished.");
            }
        }

        static void client_DataChangeNotification(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value
            if (e.Succeeded)
                Console.WriteLine($"Value: {e.AttributeData.Value}");
            else
                Console.WriteLine($"*** Failure: {e.ErrorMessageBrief}");
        }

        static void clientConnectionMonitoring_OnServerConditionChanged(object sender, EasyUAServerConditionChangedEventArgs e)
        {
            // Display the event
            Console.WriteLine(e);
        }


        // Example output:
        //
        //Reading(1)
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        //-8.095801E+32 {System.Single} @2021-06-24T07:09:46.062 @@2021-06-24T07:09:46.062; Good
        //Reading(2)
        //-3.11389E-18 {System.Single} @2021 - 06 - 24T07: 09:46.125 @@2021 - 06 - 24T07: 09:46.125; Good
        //Waiting for 10 seconds...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(Infinite); Success
        //Subscribing...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success
        //Waiting for 10 seconds...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        //Value: 3.293034E-31
        //Value: 6.838126E+37
        //Value: 5.837702E-29
        //Value: 0.02940081
        //Value: -9.653872E-17
        //Value: -1.012749E+29
        //Value: -1.422391E+20
        //Value: -3.56571E-22
        //Unsubscribing...
        //Waiting for 10 seconds...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(Infinite); Success
        //Finished.
    }
}
# This example shows how to monitor connections to and disconnections from the OPC UA server.
#
# 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 .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from Microsoft.Extensions.DependencyInjection import *
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.OperationModel import *
from OpcLabs.EasyOpc.UA.Services import *


def dataChangeNotification(sender, e):
    # Display value.
    if e.Succeeded:
        print('Value: ', e.AttributeData.Value, sep='')
    else:
        print('*** Failure: ', e.ErrorMessageBrief, sep='')

def onServerConditionChanged(sender, e):
    # Display the event.
    print(e)


endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'

# Instantiate the client object.
client = None
try:
    client = EasyUAClient()

    # Obtain the client connection monitoring service.
    clientConnectionMonitoring = ServiceProviderServiceExtensions.GetService[IEasyUAClientConnectionMonitoring](client)
    if clientConnectionMonitoring is None:
        print('The client connection monitoring service is not available.')
        exit()

    # Hook events
    client.DataChangeNotification += dataChangeNotification
    clientConnectionMonitoring.ServerConditionChanged += onServerConditionChanged

    try:
        print('Reading (1)')
        # The first read will cause a connection to the server.
        attributeData1 = IEasyUAClientExtension.Read(client,
                                                     endpointDescriptor,
                                                     UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'))
        print(attributeData1)

        print('Reading (2)')
        # The second read, because it closely follows the first one, will reuse the connection that is already
        # open.
        attributeData2 = IEasyUAClientExtension.Read(client,
                                                     endpointDescriptor,
                                                     UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'))
        print(attributeData2)

    except UAException as uaException:
        print('*** Failure: ' + uaException.GetBaseException().Message)

    print('Waiting for 10 seconds...')
    # Since the connection is now not used for some time, it will be closed.
    time.sleep(10)

    print('Subscribing...')
    # Subscribing to a monitored item will cause a connection to the server, if one is not yet open.
    IEasyUAClientExtension.SubscribeDataChange(client,
                                               endpointDescriptor,
                                               UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'),
                                               1000)

    print('Waiting for 10 seconds...')
    # The connection will not be closed as long as there are any subscriptions to the server.
    time.sleep(10)

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

    print('Waiting for 10 seconds...')
    # After some delay, the connection will be closed, because there are no subscriptions to the server.
    time.sleep(10)

    print('Finished.')

finally:
    client and client.Dispose()
' This example shows how to monitor connections to and disconnections from the OPC UA server.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports Microsoft.Extensions.DependencyInjection
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.OperationModel
Imports OpcLabs.EasyOpc.UA.Services

Namespace _EasyUAClientConnectionMonitoring
    Partial Friend Class ServerConditionChanged
        Public Shared Sub Main1()
            Dim endpointDescriptor As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object.
            Using client = New EasyUAClient()
                ' Obtain the client connection monitoring service.
                Dim clientConnectionMonitoring As IEasyUAClientConnectionMonitoring = client.GetService(Of IEasyUAClientConnectionMonitoring)
                If clientConnectionMonitoring Is Nothing Then
                    Console.WriteLine("The client connection monitoring service is not available.")
                    Exit Sub
                End If

                ' Hook events.
                AddHandler client.DataChangeNotification, AddressOf client_DataChangeNotification
                AddHandler clientConnectionMonitoring.ServerConditionChanged, AddressOf clientConnectionMonitoring_OnServerConditionChanged

                Try
                    Console.WriteLine("Reading (1)")
                    ' The first read will cause a connection to the server.
                    Dim attributeData1 As UAAttributeData = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853")
                    Console.WriteLine(attributeData1)

                    Console.WriteLine("Reading (2)")
                    ' The second read, because it closely follows the first one, will reuse the connection that is already
                    ' open.
                    Dim attributeData2 As UAAttributeData = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853")
                    Console.WriteLine(attributeData2)
                Catch uaException As UAException
                    Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message)
                End Try

                Console.WriteLine("Waiting for 10 seconds...")
                ' Since the connection is now Not used for some time, it will be closed.
                System.Threading.Thread.Sleep(10 * 1000)

                Console.WriteLine("Subscribing...")
                ' Subscribing to a monitored item will cause a connection to the server, if one is not yet open.
                client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000)

                Console.WriteLine("Waiting for 10 seconds...")
                ' The connection will not be closed as long as there are any subscriptions to the server.
                System.Threading.Thread.Sleep(10 * 1000)

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

                Console.WriteLine("Waiting for 10 seconds...")
                ' After some delay, the connection will be closed, because there are no subscriptions to the server.
                System.Threading.Thread.Sleep(10 * 1000)

                Console.WriteLine("Finished.")
            End Using
        End Sub

        Private Shared Sub client_DataChangeNotification(ByVal sender As Object, ByVal e As EasyUADataChangeNotificationEventArgs)
            ' Display value
            If e.Succeeded Then
                Console.WriteLine($"Value: {e.AttributeData.Value}")
            Else
                Console.WriteLine($"*** Failure: {e.ErrorMessageBrief}")
            End If
        End Sub

        Private Shared Sub clientConnectionMonitoring_OnServerConditionChanged(ByVal sender As Object, ByVal e As EasyUAServerConditionChangedEventArgs)
            ' Display the event
            Console.WriteLine(e)
        End Sub


        ' Example output
        '
        'Reading(1)
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        '-8.095801E+32 {System.Single} @2021-06-24T07:09:46.062 @@2021-06-24T07:09:46.062; Good
        'Reading(2)
        '-3.11389E-18 {System.Single} @2021 - 06 - 24T07: 09:46.125 @@2021 - 06 - 24T07: 09:46.125; Good
        'Waiting for 10 seconds...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(Infinite); Success
        'Subscribing...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success
        'Waiting for 10 seconds...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        'Value: 3.293034E-31
        'Value: 6.838126E+37
        'Value: 5.837702E-29
        'Value: 0.02940081
        'Value: -9.653872E-17
        'Value: -1.012749E+29
        'Value: -1.422391E+20
        'Value: -3.56571E-22
        'Unsubscribing...
        'Waiting for 10 seconds...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(Infinite); Success
        'Finished.
    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