ReadItemValue<TValue>(IEasyDAClient,ServerDescriptor,DANodeDescriptor,DAReadParameters) 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 descriptor objects for the OPC server and OPC-DA item, and specifying read parameters such as the data source or value age.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadItemValue(Of TValue)( _
   ByVal client As IEasyDAClient, _
   ByVal serverDescriptor As ServerDescriptor, _
   ByVal nodeDescriptor As DANodeDescriptor, _
   ByVal readParameters As DAReadParameters _
) As TValue

'Usage
 
Dim client As IEasyDAClient
Dim serverDescriptor As ServerDescriptor
Dim nodeDescriptor As DANodeDescriptor
Dim readParameters As DAReadParameters
Dim value As TValue
 
value = IEasyDAClientExtension2.ReadItemValue(Of TValue)(client, serverDescriptor, nodeDescriptor, readParameters)

[Extension()]
[NotNull()]
public static TValue ReadItemValue<TValue>( 
   IEasyDAClient client,
   ServerDescriptor serverDescriptor,
   DANodeDescriptor nodeDescriptor,
   DAReadParameters readParameters
)

[Extension()]
[NotNull()]
public:
static TValue^ ReadItemValuegeneric<typename TValue>
( 
   IEasyDAClient^ client,
   ServerDescriptor^ serverDescriptor,
   DANodeDescriptor^ nodeDescriptor,
   DAReadParameters^ readParameters
)

Parameters

client: The client object that will perform the operation.
serverDescriptor: The OPC server involved in the operation.
nodeDescriptor: The OPC item involved in the operation.
readParameters: Read parameters, such as the data source or value age.

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