Connectivity Software User's Guide and Reference
ReadWriteValue<TValue>(SparkplugMetric,TValue) Method
Example 



OpcLabs.EasySparkplug Assembly > OpcLabs.EasySparkplug Namespace > SparkplugMetricExtension Class > ReadWriteValue Method : ReadWriteValue<TValue>(SparkplugMetric,TValue) Method
The type of the value of the Sparkplug metric.
The Sparkplug metric that will perform the operation.

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

The initial value of the Sparkplug metric.

The value of this parameter can be null (Nothing in Visual Basic).

Makes the metric into a read-write register, specifying the typed initial value.
Syntax
'Declaration
 
<ExtensionAttribute()>
<JetBrains.Annotations.NotNullAttribute()>
Public Overloads Shared Function ReadWriteValue(Of TValue)( _
   ByVal metric As SparkplugMetric, _
   ByVal value As TValue _
) As SparkplugMetric
'Usage
 
Dim metric As SparkplugMetric
Dim value As TValue
Dim value As SparkplugMetric
 
value = SparkplugMetricExtension.ReadWriteValue(Of TValue)(metric, value)
[Extension()]
[JetBrains.Annotations.NotNull()]
public static SparkplugMetric ReadWriteValue<TValue>( 
   SparkplugMetric metric,
   TValue value
)
[Extension()]
[JetBrains.Annotations.NotNull()]
public:
static SparkplugMetric^ ReadWriteValuegeneric<typename TValue>
( 
   SparkplugMetric^ metric,
   TValue^ value
) 

Parameters

metric
The Sparkplug metric that will perform the operation.

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

value
The initial value of the Sparkplug metric.

The value of this parameter can be null (Nothing in Visual Basic).

Type Parameters

TValue
The type of the value of the Sparkplug metric.

Return Value

Returns the metric, internally modified as defined by the method.

This method never returns 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

This method overload infers the Sparkplug data type of the metric 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.

 

Sparkplug is a trademark of Eclipse Foundation, Inc. "MQTT" is a trademark of the OASIS Open standards consortium. Other related terms are trademarks of their respective owners. Any use of these terms on this site is for descriptive purposes only and does not imply any sponsorship, endorsement or affiliation.

Example
// This example shows how to create a read-write metric that behaves like a register, specifying initial value.
//
// You can use any Sparkplug application, including our SparkplugCmd utility and the SparkplugApplicationConsoleDemo
// program, to subscribe to the edge node data. SparkplugCmd, or other capable Sparkplug application, can be used to write
// data into the metric.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-ConnectivityStudio/Latest/examples.html .
// Sparkplug examples in C# on GitHub: https://github.com/OPCLabs/Examples-ConnectivityStudio-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 OpcLabs.EasySparkplug;
using System;

namespace SparkplugDocExamples.EdgeNode._SparkplugMetric
{
    partial class ReadWriteValue
    {
        static public void Main1()
        {
            // Note that the default port for the "mqtt" scheme is 1883.
            var hostDescriptor = new SparkplugHostDescriptor("mqtt://localhost");

            // Instantiate the edge node object and hook events.
            var edgeNode = new EasySparkplugEdgeNode(hostDescriptor, "easyGroup", "easySparkplugDemo");
            edgeNode.SystemConnectionStateChanged += (sender, eventArgs) =>
            {
                // Display the new connection state (such as when the connection to the broker succeeds or fails).
                Console.WriteLine($"{nameof(EasySparkplugEdgeNode.SystemConnectionStateChanged)}: {eventArgs}");
            };

            // Create a metric that is a read-write register, defining its initial value.
            // The type of the metric (Int32, in this case) is inferred from the initial value.
            edgeNode.Add(new SparkplugMetric("MyMetric").ReadWriteValue(42));

            // Start the edge node.
            Console.WriteLine("The edge node is starting...");
            edgeNode.Start();

            Console.WriteLine("The edge node is started.");
            Console.WriteLine();

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

            // Stop the edge node.
            Console.WriteLine("The edge node is stopping...");
            edgeNode.Stop();

            Console.WriteLine("The edge node is stopped.");
        }
    }
}
' This example shows how to create a read-write metric that behaves like a register, specifying initial value.
'
' You can use any Sparkplug application, including our SparkplugCmd utility and the SparkplugApplicationConsoleDemo
' program, to subscribe to the edge node data. SparkplugCmd, or other capable Sparkplug application, can be used to write
' data into the metric.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-ConnectivityStudio/Latest/examples.html .
' Sparkplug examples in C# on GitHub: https://github.com/OPCLabs/Examples-ConnectivityStudio-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.

Imports OpcLabs.EasySparkplug

Namespace Global.SparkplugDocExamples.EdgeNode._SparkplugMetric
    Partial Class ReadWriteValue
        Public Shared Sub Main1()
            ' Note that the default port for the "mqtt" scheme is 1883.
            Dim hostDescriptor = New SparkplugHostDescriptor("mqtt://localhost")

            ' Instantiate the edge node object and hook events.
            Dim edgeNode = New EasySparkplugEdgeNode(hostDescriptor, "easyGroup", "easySparkplugDemo")
            AddHandler edgeNode.SystemConnectionStateChanged,
                Sub(sender, eventArgs)
                    ' Display the new connection state (such as when the connection to the broker succeeds or fails).
                    Console.WriteLine($"{NameOf(EasySparkplugEdgeNode.SystemConnectionStateChanged)}: {eventArgs}")
                End Sub

            ' Create a metric that is a read-write register, defining its initial value.
            ' The type of the metric (Int32, in this case) is inferred from the initial value.
            edgeNode.Add(New SparkplugMetric("MyMetric").ReadWriteValue(42))

            ' Start the edge node.
            Console.WriteLine("The edge node is starting...")
            edgeNode.Start()

            Console.WriteLine("The edge node is started.")
            Console.WriteLine()

            ' Let the user decide when to stop.
            Console.WriteLine("Press Enter to stop the edge node...")
            Console.ReadLine()

            ' Stop the edge node.
            Console.WriteLine("The edge node is stopping...")
            edgeNode.Stop()

            Console.WriteLine("The edge node 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

See Also