ReadFunction<TValue>(UADataVariable,Func<UAAttributeData<TValue>>) Method

Specifies read function returning typed attribute data, for the pull data provision model.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadFunction(Of TValue)( _
   ByVal dataVariable As UADataVariable, _
   ByVal readFunction As Func(Of UAAttributeData(Of TValue)) _
) As UADataVariable

'Usage
 
Dim dataVariable As UADataVariable
Dim readFunction As Func(Of UAAttributeData(Of TValue))
Dim value As UADataVariable
 
value = UADataVariableExtension.ReadFunction(Of TValue)(dataVariable, readFunction)

[Extension()]
[NotNull()]
public static UADataVariable ReadFunction<TValue>( 
   UADataVariable dataVariable,
   Func<UAAttributeData<TValue>> readFunction
)

[Extension()]
[NotNull()]
public:
static UADataVariable^ ReadFunctiongeneric<typename TValue>
( 
   UADataVariable^ dataVariable,
   Func<UAAttributeData<TValue^>^>^ readFunction
)

Parameters

dataVariable: The data variable that will be modified and returned.
The value of this parameter cannot be null (Nothing in Visual Basic).
readFunction: The read function, i.e. the function that performs the read operation and returns the attribute data that will be returned to the caller of the OPC UA Read.
The value of this parameter cannot be null (Nothing in Visual Basic).

Type Parameters

TValue: The type of the value of the data variable.

Return Value

Returns the , internally modified as defined by the method.

This method never returns null (Nothing in Visual Basic).

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.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.

Remarks

This method overload infers the OPC data type and value rank of the data variable from the TValue type.

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 create a data variable and implement reading its attribute data using a function.
// 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.Generic;
using OpcLabs.EasyOpc.UA.NodeSpace;

namespace UAServerDocExamples._UADataVariable
{
    partial class ReadFunction
    {
        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 data variable, defining its read attribute data (including status code and source timestamp) by a
            // function.
            // The type of the data variable (Int32, in this case) is inferred from the type returned by the function.
            var random = new Random();
            server.Add(new UADataVariable("ReadThisVariable").ReadFunction(() => new UAAttributeData<int>(
                random.Next(), DateTime.UtcNow.AddMinutes(-10))));

            // 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 create a data variable and implement reading its attribute data using a function.
' 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.Generic
Imports OpcLabs.EasyOpc.UA.NodeSpace

Namespace _UADataVariable
    Partial Friend Class ReadFunction
        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 data variable, defining its read attribute data (including status code and source timestamp) by a
            ' function.
            ' The type of the data variable (Int32, in this case) is inferred from the type returned by the function.
            Dim random = New Random()
            server.Add(New UADataVariable("ReadThisVariable").ReadFunction(Function() New UAAttributeData(Of Integer)(
                random.Next(), DateTime.UtcNow.AddMinutes(-10))))

            ' 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

CSharp
VB.NET

// This example shows how to create a data variable and implement reading its attribute data using a function, providing
// "Good" or "Bad" status code as needed.
// 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.Generic;
using OpcLabs.EasyOpc.UA.NodeSpace;

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

            // Create a data variable, defining its read attribute data (including status code and source timestamp) by a
            // function. Alternate "Good" and "Bad" status codes randomly.
            // The type of the data variable (Int32, in this case) is inferred from the type returned by the function.
            var random = new Random();
            server.Add(new UADataVariable("ReadThisVariable").ReadFunction(() => new UAAttributeData<int>(
                value: 42,
                (random.Next(2) != 0) ? UACodeBits.Good : UACodeBits.BadNoCommunication,
                DateTime.UtcNow)));

            // 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 create a data variable and implement reading its attribute data using a function, providing
' "Good" or "Bad" status code as needed.
' 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 Newtonsoft.Json.Linq
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.Generic
Imports OpcLabs.EasyOpc.UA.NodeSpace

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

            ' Create a data variable, defining its read attribute data (including status code and source timestamp) by a
            ' function. Alternate "Good" and "Bad" status codes randomly.
            ' The type of the data variable (Int32, in this case) is inferred from the type returned by the function.
            Dim random = New Random()
            server.Add(New UADataVariable("ReadThisVariable").ReadFunction(Function() New UAAttributeData(Of Integer)(
                42,
                If(random.Next(2) <> 0, UACodeBits.Good, UACodeBits.BadNoCommunication),
                DateTime.UtcNow)))

            ' 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

UADataVariableExtension Class
UADataVariableExtension Members
Overload List

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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.