QuickOPC User's Guide and Reference
ReadItem<TValue>(IEasyDAClient,ServerDescriptor,DANodeDescriptor) Method



OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.DataAccess.Extensions Namespace > IEasyDAClientExtension2 Class > ReadItem Method : ReadItem<TValue>(IEasyDAClient,ServerDescriptor,DANodeDescriptor) Method
The type of item value.
The client object that will perform the operation.
The OPC server involved in the operation.
The OPC item involved in the operation.
Reads a typed named item from an OPC server. A typed value, quality and timestamp are returned. Reads a typed named item using descriptor objects for the OPC server and OPC-DA item.
Syntax
'Declaration
 

<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadItem(Of TValue)( _
   ByVal client As IEasyDAClient, _
   ByVal serverDescriptor As ServerDescriptor, _
   ByVal nodeDescriptor As DANodeDescriptor _
) As DAVtq(Of TValue)
'Usage
 

Dim client As IEasyDAClient
Dim serverDescriptor As ServerDescriptor
Dim nodeDescriptor As DANodeDescriptor
Dim value As DAVtq(Of TValue)
 
value = IEasyDAClientExtension2.ReadItem(Of TValue)(client, serverDescriptor, nodeDescriptor)
[Extension()]
[NotNull()]
public static DAVtq<TValue> ReadItem<TValue>( 
   IEasyDAClient client,
   ServerDescriptor serverDescriptor,
   DANodeDescriptor nodeDescriptor
)
[Extension()]
[NotNull()]
public:
static DAVtq<TValue^>^ ReadItemgeneric<typename TValue>
( 
   IEasyDAClient^ client,
   ServerDescriptor^ serverDescriptor,
   DANodeDescriptor^ nodeDescriptor
)

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.

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
ExceptionDescription
OpcLabs.EasyOpc.OperationModel.OpcExceptionThrown when the OPC operation fails.
System.ArgumentNullExceptionA 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

See Also

Reference

IEasyDAClientExtension2 Class
IEasyDAClientExtension2 Members
Overload List

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