WriteValueAction<TValue>(UADataVariable,Type,Action<TValue>) Method

Makes data variable that consumes the attribute data using the write value action. Specify the declared type.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function WriteValueAction(Of TValue)( _
   ByVal dataVariable As UADataVariable, _
   ByVal declaredType As Type, _
   ByVal writeValueAction As Action(Of TValue) _
) As UADataVariable

'Usage
 
Dim dataVariable As UADataVariable
Dim declaredType As Type
Dim writeValueAction As Action(Of TValue)
Dim value As UADataVariable
 
value = UADataVariableExtension.WriteValueAction(Of TValue)(dataVariable, declaredType, writeValueAction)

[Extension()]
[NotNull()]
public static UADataVariable WriteValueAction<TValue>( 
   UADataVariable dataVariable,
   Type declaredType,
   Action<TValue> writeValueAction
)

[Extension()]
[NotNull()]
public:
static UADataVariable^ WriteValueActiongeneric<typename TValue>
( 
   UADataVariable^ dataVariable,
   Type^ declaredType,
   Action<TValue^>^ writeValueAction
)

Parameters

dataVariable: The data variable that will be modified and returned.
The value of this parameter cannot be null (Nothing in Visual Basic).
declaredType: The declared type of the data variable, expressed as .NET System.Type.
The value of this parameter cannot be null (Nothing in Visual Basic).
writeValueAction: The write value action, i.e. the action that accepts the value to be written and performs the write operation.
The value of this parameter cannot be null (Nothing in Visual Basic).

Type Parameters

TValue

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 always makes the data variable writable; however, its status code and source timestamp will not be writable, i.e. OPC UA clients will not be able to modify them. If you need a different behavior, use one of the WriteFunction(UADataVariable,Type,Func<UAAttributeData,UAStatusCode>) method overloads instead.

This method does not change the readability access of the data variable. By default, data variables are readable. If you need a data variable that is writable but non-readable, combine this method with calling Readable(UADataVariable,Boolean) method with the 'readable' parameter set to false.

Unless the write value action throws a OpcLabs.EasyOpc.UA.UAStatusCodeException, a "Good" status code will be returned as the outcome of the OPC UA write operation. If the write value action function throws OpcLabs.EasyOpc.UA.UAStatusCodeException, the OpcLabs.EasyOpc.UA.UAStatusCodeException.StatusCode of the exception will become the outcome of the OPC UA write operation. For performance reasons, however, if you want to return status codes other than "Good" as OPC UA write operation outcomes, it is recommended that you use one of the WriteValueFunction<TValue>(UADataVariable,Type,Func<TValue,UAStatusCode>) method overloads instead. With these methods, you specify a write value function that returns the OpcLabs.EasyOpc.UA.UAStatusCode that is the OPC UA write operation outcome, allowing the status code be passed without the ineffective throwing and catching of the OpcLabs.EasyOpc.UA.UAStatusCodeException.

This method overload infers the OPC data type and value rank of the data variable from the declaredType parameter. The type used in your code to implement the data variable behavior can be different, and it will be TValue. OPC Wizard provides automatic value conversions. This can be useful in case your language makes it more difficult to process some .NET types, as is the case e.g. with VB.NET and unsigned integer types such as System.UInt32. In this case, for example, if you want a data variable of OPC type UInt32, you can set declaredType to System.UInt32, but use a System.Int64 as the type of your action argument (TValue).

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 define a data variable of OPC data type UInt16 and use an action to its write behavior.
// This is an example of the push data consumption model.
// 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;

namespace UAServerDocExamples._UADataVariable
{
    partial class WriteValueAction
    {
        public static void UInt16()
        {
            // Instantiate the server object.
            // By default, the server will run on endpoint URL "opc.tcp://localhost:48040/".
            var server = new EasyUAServer();

            // Create a writable data variable and add an action that will be executed when the data variable is written to.
            // We explicitly specify the OPC data type of the variable to be UInt16, but use .NET Int32 in the write value
            // function. The OPC Wizard will attempt to convert the value being written to the specified .NET type. This is
            // helpful in languages like VB.NET that do not have full support for some types (such as unsigned integers).
            server.Add(new UADataVariable("WriteToThisVariable").WriteValueAction<int>(
                typeof(UInt16),
                value => Console.WriteLine($"Value written: {value}")));

            // Start the server.
            Console.WriteLine("The server is starting...");
            server.Start();

            Console.WriteLine("The server is started.");
            Console.WriteLine("Any value written to the example data variable will be displayed on the console.");
            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 define a data variable of OPC data type UInt16 and use an action to its write behavior.
' This is an example of the push data consumption model.
' 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

Namespace _UADataVariable
    Partial Friend Class WriteValueAction
        Shared Sub UInt16()
            ' Instantiate the server object.
            ' By default, the server will run on endpoint URL "opc.tcp://localhost:48040/".
            Dim server = New EasyUAServer()

            ' Create a writable data variable and add an action that will be executed when the data variable is written to.
            ' We explicitly specify the OPC data type of the variable to be UInt16, but use .NET Int32 in the write value
            ' function. The OPC Wizard will attempt to convert the value being written to the specified .NET type. This is
            ' helpful in languages like VB.NET that do not have full support for some types (such as unsigned integers).
            server.Add(New UADataVariable("WriteToThisVariable").WriteValueAction(Of Integer)(
                GetType(UInt16),
                Sub(value) Console.WriteLine($"Value written: {value}")))

            ' Start the server.
            Console.WriteLine("The server is starting...")
            server.Start()

            Console.WriteLine("The server is started.")
            Console.WriteLine("Any value written to the example data variable will be displayed on the console.")
            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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