OnNext(IUADataSubscription,Object) Method

Provides the data subscription with an updated value.

Syntax

[Extension()]
public static void OnNext( 
   IUADataSubscription dataSubscription,
   object updateValue
)

[Extension()]
public:
static void OnNext( 
   IUADataSubscription^ dataSubscription,
   Object^ updateValue
)

'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Sub OnNext( _
   ByVal dataSubscription As IUADataSubscription, _
   ByVal updateValue As Object _
)

'Usage
 
Dim dataSubscription As IUADataSubscription
Dim updateValue As Object
 
IUADataSubscriptionExtension.OnNext(dataSubscription, updateValue)

Parameters

dataSubscription: The data subscription that receives the data.
The value of this parameter cannot be null (Nothing in Visual Basic).
updateValue: The new value of the data variable.
The value of this parameter can be null (Nothing in Visual Basic).

Remarks

This method is useful, as it combines the construction of the OpcLabs.EasyOpc.UA.UAAttributeData with obtaining the source timestamp and sending the attribute data to the data subscription. The source timestamp is set to the current time, and the status code is set to "Good". If your server provides its own source timestamps, do not use this method overload, construct the OpcLabs.EasyOpc.UA.UAAttributeData yourself and call OpcLabs.BaseLib.ISink<T>.OnNext method directly.

Data polling must not be effect on the associated data variable, otherwise the update will be discarded. For more details, see UADataVariable.UseDataPolling. In most cases, the data polling is suppressed for you automatically.

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

CSharp
VB.NET

// 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.");
        }
    }
}

' 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 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
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.NodeSpace
Imports Timer = System.Timers.Timer

Namespace _UAServerNode
    Partial Friend Class DataSubscriptionChanged
        Shared Sub Main1()
            ' Instantiate the server object.
            ' By default, the server will run on endpoint URL "opc.tcp://localhost:48040/".
            Dim server = New EasyUAServer()

            ' Create a read-only data variable.
            Dim random = New Random()
            Dim dataVariable = UADataVariable.CreateIn(server.Objects, "SubscribeToThisVariable") _
                .ValueType(Of Integer)() _
                .Writable(False)

            dataVariable.UseDataPolling = False ' Recommended, but not strictly necessary.
            AddHandler dataVariable.DataSubscriptionChanged, Sub(sender, args)
                                                                 Select Case args.Action
                                                                     Case UADataSubscriptionChangedAction.Add
                                                                         ' Obtain the sampling interval from the data subscription.
                                                                         Dim samplingInterval As Integer = 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.
                                                                         Dim timer = New Timer With {.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.
                                                                         AddHandler timer.Elapsed, Sub(s, e) args.DataSubscription.OnNext(random.Next())

                                                                         ' Start the subscription timer.
                                                                         timer.Start()

                                                                     Case UADataSubscriptionChangedAction.Remove
                                                                         Console.WriteLine("Data subscription removed")

                                                                         ' Dispose of the subscription timer (stopping it too).
                                                                         Dim timer As Timer = CType(args.DataSubscription.State, Timer)
                                                                         timer.Dispose()

                                                                     Case UADataSubscriptionChangedAction.Modify
                                                                         Dim samplingInterval As Integer = args.DataSubscription.SamplingInterval
                                                                         Console.WriteLine($"Data subscription modified, sampling interval: {samplingInterval}")

                                                                         ' Change the interval of the subscription timer.
                                                                         Dim timer As Timer = CType(args.DataSubscription.State, Timer)
                                                                         timer.Interval = samplingInterval
                                                                 End Select
                                                             End Sub

            ' The read behavior of the data variable needs to be defined as well, separately from the data subscriptions.
            dataVariable.ReadValueFunction(Function() 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.")
        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

IUADataSubscriptionExtension Class
IUADataSubscriptionExtension Members
Overload List
UseDataPolling Property

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