ReadItemValueDouble(IEasyDAClient,String,String,String) Method

Reads a value of named OPC item, and converts it to System.Double. The value is requested from the OPC server using a corresponding data type.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function ReadItemValueDouble( _
   ByVal client As IEasyDAClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String _
) As Double

'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim value As Double
 
value = IEasyDAClientExtension2.ReadItemValueDouble(client, machineName, serverClass, itemId)

[Extension()]
public static double ReadItemValueDouble( 
   IEasyDAClient client,
   string machineName,
   string serverClass,
   string itemId
)

[Extension()]
public:
static double ReadItemValueDouble( 
   IEasyDAClient^ client,
   String^ machineName,
   String^ serverClass,
   String^ itemId
)

Parameters

client: The client object that will perform the operation.
machineName: Name of the machine. Determines the computer on which the OPC server is located. It may be an empty string, in which case the OPC server is assumed to exist on the local computer or at the computer specified for it by DCOM configuration.
serverClass: Contains ProgID of the OPC server to read from.
itemId: Contains OPC item identifier.

Return Value

Returns a value of the OPC item, converted to a type indicated by the method name.

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.

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

IEasyDAClientExtension2 Class
IEasyDAClientExtension2 Members
Overload List

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