OPC Studio User's Guide and Reference
DataSubscription Property
Example 



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OpcLabs.ServerOpcUA Assembly > OpcLabs.EasyOpc.UA.OperationModel Namespace > UADataSubscriptionChangedEventArgs Class : DataSubscription Property
Contains the data subscription that is the subject of the change.
Syntax
'Declaration
 
<NotNullAttribute()>
Public Property DataSubscription As IUADataSubscription
 
'Usage
 
Dim instance As UADataSubscriptionChangedEventArgs
Dim value As IUADataSubscription
 
instance.DataSubscription = value
 
value = instance.DataSubscription

Property Value

The OpcLabs.EasyOpc.UA.NodeSpace.IUADataSubscription instance that represents the data subscription being added, removed, or modified.

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

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

Use the data subscription's OpcLabs.BaseLib.ISink<T>.OnNext method to provide data updates to the data variable.

This property also allows access to the data subscription details, enabling further actions or evaluations based on the subscription's current state and configuration.

Example
// This example shows how to implement own handling of data subscriptions.
// You can use any OPC UA client, including our Connectivity Explorer and OpcCmd utility, to connect to the server. 
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client, server and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-OPCStudio-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 OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.NodeSpace;
using Timer = System.Timers.Timer;

namespace UAServerDocExamples._UAServerNode
{
    class DataSubscriptionChanged
    {
        public static void Main1()
        {
            // Instantiate the server object.
            // By default, the server will run on endpoint URL "opc.tcp://localhost:48040/".
            var server = new EasyUAServer();

            // Create a read-only data variable.
            var random = new Random();
            var dataVariable = UADataVariable.CreateIn(server.Objects, "SubscribeToThisVariable")
                .ValueType<int>()
                .Writable(false);

            dataVariable.UseDataPolling = false;    // Recommended, but not strictly necessary.
            dataVariable.DataSubscriptionChanged += (sender, args) =>
            {
                switch (args.Action)
                {
                    case UADataSubscriptionChangedAction.Add:
                    {
                        // Obtain the sampling interval from the data subscription.
                        int samplingInterval = args.DataSubscription.SamplingInterval;
                        Console.WriteLine($"Data subscription added, sampling interval: {samplingInterval}");

                        // Create a timer that will provide the data variable with a new data. In a real server the activity
                        // may also come from other sources.
                        var timer = new Timer { AutoReset = true, Interval = samplingInterval };
                        args.DataSubscription.State = timer;

                        // Set the read attribute data of the data variable to a random value whenever the timer interval elapses.
                        timer.Elapsed += (s, e) => args.DataSubscription.OnNext(random.Next());

                        // Start the subscription timer.
                        timer.Start();
                        break;
                    }

                    case UADataSubscriptionChangedAction.Remove:
                    {
                        Console.WriteLine("Data subscription removed");

                        // Dispose of the subscription timer (stopping it too).
                        var timer = (Timer)args.DataSubscription.State;
                        timer.Dispose();
                        break;
                    }

                    case UADataSubscriptionChangedAction.Modify:
                    {
                        int samplingInterval = args.DataSubscription.SamplingInterval;
                        Console.WriteLine($"Data subscription modified, sampling interval: {samplingInterval}");

                        // Change the interval of the subscription timer.
                        var timer = (Timer)args.DataSubscription.State;
                        timer.Interval = samplingInterval;
                        break;
                    }
                }
                args.Handled = true;    // Do not forget to indicate that your code has handled the event.
            };

            // The read behavior of the data variable needs to be defined as well, separately from the data subscriptions.
            dataVariable.ReadValueFunction(() => random.Next());
            
            // Start the server.
            Console.WriteLine("The server is starting...");
            server.Start();

            Console.WriteLine("The server is started.");
            Console.WriteLine();

            // Let the user decide when to stop.
            Console.WriteLine("Press Enter to stop the server...");
            Console.ReadLine();

            // Stop the server.
            Console.WriteLine("The server is stopping...");
            server.Stop();

            Console.WriteLine("The server is stopped.");
        }
    }
}
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