ReadItemValue<TValue>(IEasyDAClient,String,String,String) Method

Reads a typed named item from an OPC server. Only the item's typed value is returned (quality and timestamp are not returned). Reads a value of typed named item using individual parameters specifying its location.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadItemValue(Of TValue)( _
   ByVal client As IEasyDAClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String _
) As TValue

'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim value As TValue
 
value = IEasyDAClientExtension2.ReadItemValue(Of TValue)(client, machineName, serverClass, itemId)

[Extension()]
[NotNull()]
public static TValue ReadItemValue<TValue>( 
   IEasyDAClient client,
   string machineName,
   string serverClass,
   string itemId
)

[Extension()]
[NotNull()]
public:
static TValue^ ReadItemValuegeneric<typename TValue>
( 
   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. 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.

Type Parameters

TValue: The type of item value.

Return Value

If successful, the function returns the actual, typed value of OPC item requested.

Exceptions

Exception	Description
OpcLabs.EasyOpc.OperationModel.OpcException	Thrown when the OPC operation fails.
System.ArgumentNullException	A `null` reference (`Nothing` in Visual Basic) is passed to a method that does not accept it as a valid argument.

Remarks

The server can be local or can be remotely accessed via DCOM. Optionally, an access path can be specified or a specific data type can be requested.

Use this method if you are only interested in the actual typed value of the OPC item. Use ReadItem method if you also need the quality or timestamp. The ReadItemValue method makes it very easy to obtain the actual typed data value with just one function call.

The ReadItemValue method waits until the quality becomes "good", or the timeout elapses.

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2012, Windows Server 2016; .NET Core, .NET 5, .NET 6: Linux, macOS, Microsoft Windows

Reference

IEasyDAClientExtension2 Class
IEasyDAClientExtension2 Members
Overload List