ReadValue(IEasyUAClient,UANodeArguments,UAReadParameters) Method

Reads a value of Value attribute of a node, using an object that holds the node information, and a read parameters object.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<CanBeNullAttribute()>
Public Overloads Shared Function ReadValue( _
   ByVal client As IEasyUAClient, _
   ByVal nodeArguments As UANodeArguments, _
   ByVal readParameters As UAReadParameters _
) As Object

'Usage
 
Dim client As IEasyUAClient
Dim nodeArguments As UANodeArguments
Dim readParameters As UAReadParameters
Dim value As Object
 
value = IEasyUAClientExtension.ReadValue(client, nodeArguments, readParameters)

[Extension()]
[CanBeNull()]
public static object ReadValue( 
   IEasyUAClient client,
   UANodeArguments nodeArguments,
   UAReadParameters readParameters
)

[Extension()]
[CanBeNull()]
public:
static Object^ ReadValue( 
   IEasyUAClient^ client,
   UANodeArguments^ nodeArguments,
   UAReadParameters^ readParameters
)

Parameters

client

The client object that will perform the operation.

This is typically the EasyUAClient object.

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

nodeArguments

An object that specifies the node in the OPC server.

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

readParameters

Read parameters, such as the maximum age of the value.

Because the UAReadParameters has implicit conversions from System.Double and OpcLabs.EasyOpc.UA.AddressSpace.UAQualifiedName, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a double precision floating point number (representing the maximum value age in milliseconds), or an OPC UA qualified name (representing the name of the encoding to be used) in place of this parameter, and the corresponding OPC UA read parameters will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the UAReadParameters.FromDouble or UAReadParameters.FromUAQualifiedName static method instead.

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

Return Value

If successful, the method returns the actual value of OPC attribute requested.

This method can return 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.
OpcLabs.EasyOpc.UA.OperationModel.UAException	The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause. This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

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.

OpcLabs.EasyOpc.UA.OperationModel.UAException

The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause.

This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

Remarks

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.

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

IEasyUAClientExtension Class
IEasyUAClientExtension Members
Overload List

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