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

Reads a typed named item from an OPC server. A typed value, quality and timestamp are returned. Reads a typed named item using individual parameters specifying its location, and a specific data type.

Syntax

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

[Extension()]
[NotNull()]
public:
static DAVtq<TValue^>^ ReadItemgeneric<typename TValue>
( 
   IEasyDAClient^ client,
   String^ machineName,
   String^ serverClass,
   String^ itemId
)

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

'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim value As DAVtq(Of TValue)
 
value = IEasyDAClientExtension2.ReadItem(Of TValue)(client, machineName, serverClass, 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 a OpcLabs.EasyOpc.DataAccess.Generic.DAVtq<TValue> object. The object contains the value, timestamp and quality of the 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.

The ReadItem method only waits for the first update from the server (or until the timeout elapses); it does not wait until the quality becomes "uncertain" or "good".

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