Read Event (EasyUAServerCore)

Raised to obtain the OPC UA read data.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
Public Event Read As UADataVariableReadEventHandler

'Usage
 
Dim instance As EasyUAServerCore
Dim handler As UADataVariableReadEventHandler
 
AddHandler instance.Read, handler

public event UADataVariableReadEventHandler Read

public:
event UADataVariableReadEventHandler^ Read

Event Data

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

Property	Description
DataVariable	The data variable being processed. (Inherited from OpcLabs.EasyOpc.UA.OperationModel.UADataVariableProcessedEventArgs)
Handled	(Inherited from System.ComponentModel.HandledEventArgs)
Result	The value/timestamps/status code that is the result of the OPC read.

Remarks

This event is triggered when data is requested to be read from the OPC UA server. Event handlers attached to this event are expected to provide the data for the read operation. It is an essential mechanism for custom data provisioning in response to OPC client read requests.

The event handlers for this event should not throw any exceptions. If an exception is thrown from the event handler, it might be reported through debugging, tracing or logging facilities, but the processing continues as normally, i.e. the invocation of remaining handlers, and the outcome of the Read operation, are not influenced.

Example

CSharp
VB.NET

// This example shows how to handle the read event on a folder, providing a way to implement reading of multiple data
// variables using a single handler.
// 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.BaseLib.NodeSpace;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.NodeSpace;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UAServerDocExamples._UAServerNode
{
    class Read
    {
        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 folder node.
            UAFolder myFolder = UAFolder.CreateIn(server.Objects, "MyFolder");

            // Create data variables in the folder. Distinguish them by their state.
            myFolder.Add(new UADataVariable("MyDataVariable1").ValueType<int>().SetState(1));
            myFolder.Add(new UADataVariable("MyDataVariable2").ValueType<int>().SetState(2));
            myFolder.Add(new UADataVariable("MyDataVariable3").ValueType<int>().SetState(3));
            myFolder.Add(new UADataVariable("MyDataVariable4").ValueType<int>().SetState(4));
            myFolder.Add(new UADataVariable("MyDataVariable5").ValueType<int>().SetState(5));

            // Handle the read event for the folder.
            myFolder.Read += MyFolderOnRead;

            // 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.");
        }

        /// <summary>
        /// Event handler for the read event on the folder. 
        /// </summary>
        /// <param name="sender">The folder object that sends the event.</param>
        /// <param name="e">Data for the variable read event.</param>
        static private void MyFolderOnRead(object sender, UADataVariableReadEventArgs e)
        {
            // Obtain the state associated with the data variable that is being read.
            // Use it as the offset for the random value, so that each data variable generates values in a unique range.
            int offset = (int)e.DataVariable.State*100;

            // Generate a random value, indicate that the read has been handled, and return the generated value.
            e.HandleAndReturn(Random.Next(offset, offset + 100));
        }

        static private readonly Random Random = new Random();
    }
}

' This example shows how to handle the read event on a folder, providing a way to implement reading of multiple data
' variables using a single handler.
' 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.BaseLib.NodeSpace
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.NodeSpace
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _UAServerNode
    Partial Friend Class Read
        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 folder node.
            Dim myFolder As UAFolder = UAFolder.CreateIn(server.Objects, "MyFolder")

            ' Create data variables in the folder. Distinguish them by their state.
            myFolder.Add(New UADataVariable("MyDataVariable1").ValueType(Of Integer)().SetState(1))
            myFolder.Add(New UADataVariable("MyDataVariable2").ValueType(Of Integer)().SetState(2))
            myFolder.Add(New UADataVariable("MyDataVariable3").ValueType(Of Integer)().SetState(3))
            myFolder.Add(New UADataVariable("MyDataVariable4").ValueType(Of Integer)().SetState(4))
            myFolder.Add(New UADataVariable("MyDataVariable5").ValueType(Of Integer)().SetState(5))

            ' Handle the read event for the folder.
            AddHandler myFolder.Read, AddressOf MyFolderOnRead

            ' 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

        ''' <summary>
        ''' Event handler for the read event on the folder.  
        ''' </summary>
        ''' <param name="sender">The data variable object that sends the event.</param>
        ''' <param name="e">Data for the variable read event.</param>
        Private Shared Sub MyFolderOnRead(ByVal sender As Object, ByVal e As UADataVariableReadEventArgs)
            ' Obtain the state associated with the data variable that is being read.
            ' Use it as the offset for the random value, so that each data variable generates values in a unique range.
            Dim offset As Integer = CInt(e.DataVariable.State * 100)

            ' Generate a random value, indicate that the read has been handled, and return the generated value.
            e.HandleAndReturn(Random.Next(offset, offset + 100))
        End Sub

        Private Shared ReadOnly Random As Random = New Random()
    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

EasyUAServerCore Class
EasyUAServerCore Members

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Missing some example? Ask us for it on our Online Forums! You do not have to own a commercial license in order to use Online Forums, and we reply to every post.