ReadItem(IEasyDAClient,DAReadItemArguments) Method

Reads a named item using an object that holds all necessary arguments. Value, quality and timestamp are returned.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadItem( _
   ByVal client As IEasyDAClient, _
   ByVal readItemArguments As DAReadItemArguments _
) As DAVtq

'Usage
 
Dim client As IEasyDAClient
Dim readItemArguments As DAReadItemArguments
Dim value As DAVtq
 
value = IEasyDAClientExtension.ReadItem(client, readItemArguments)

[Extension()]
[NotNull()]
public static DAVtq ReadItem( 
   IEasyDAClient client,
   DAReadItemArguments readItemArguments
)

[Extension()]
[NotNull()]
public:
static DAVtq^ ReadItem( 
   IEasyDAClient^ client,
   DAReadItemArguments^ readItemArguments
)

Parameters

client

The client object that will perform the operation.

This is typically the EasyDAClient object.

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

readItemArguments

Arguments specifying what to read from an OPC-DA server.

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

Return Value

If successful, the function returns a DAVtq object. The object contains the value, timestamp and quality of the OPC item requested.

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.
OpcLabs.EasyOpc.OperationModel.OpcException	The OPC "Classic" (or OPC XML-DA) 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.OperationModel.OpcException

The OPC "Classic" (or OPC XML-DA) 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

IEasyDAClientExtension Class
IEasyDAClientExtension Members
Overload List

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