ReadValue(IEasyUAClient,UANodeArguments,UAAttributeId) Method

Reads an attribute from an OPC server. Only the attribute's value is returned (status code and timestamps are not returned). Reads a value of a specified attribute of a node, using an object that holds the node information, and an attribute Id.

Syntax

Visual Basic
C#
C++/CLI

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

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

[Extension()]
[CanBeNull()]
public static object ReadValue( 
   IEasyUAClient client,
   UANodeArguments nodeArguments,
   UAAttributeId attributeId
)

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

Parameters

client: The client object that will perform the operation.
nodeArguments: An object that specifies the node in the OPC server.
attributeId: Attribute Id. Identifies an attribute of a node.

Return Value

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

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.ComponentModel.InvalidEnumArgumentException	An invalid enumeration value was used. 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.

System.ComponentModel.InvalidEnumArgumentException

An invalid enumeration value was used.

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

The status code must be 'good' for this method to succeed; otherwise, a OpcLabs.EasyOpc.UA.OperationModel.UAException is thrown.

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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