'Declaration
 
<ExtensionAttribute()>
<JetBrains.Annotations.NotNullAttribute()>
Public Overloads Shared Function ReadItem( _
   ByVal client As IEasyDAClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String, _
   ByVal dataType As VarType, _
   ByVal valueAge As Integer _
) As DAVtq

'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim dataType As VarType
Dim valueAge As Integer
Dim value As DAVtq
 
value = IEasyDAClientExtension.ReadItem(client, machineName, serverClass, itemId, dataType, valueAge)

[Extension()]
[JetBrains.Annotations.NotNull()]
public static DAVtq ReadItem( 
   IEasyDAClient client,
   string machineName,
   string serverClass,
   string itemId,
   VarType dataType,
   int valueAge
)

[Extension()]
[JetBrains.Annotations.NotNull()]
public:
static DAVtq^ ReadItem( 
   IEasyDAClient^ client,
   String^ machineName,
   String^ serverClass,
   String^ itemId,
   VarType^ dataType,
   int valueAge
) 

Parameters

client

The client object that will perform the operation.

This is typically the EasyDAClient object.

The value of this parameter cannot be null (Nothing in Visual Basic).

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.

The value represents a UNC or DNS computer name. Any string can be passed to this parameter (i.e. will not cause System.ArgumentException), but not all values make sense and will work when an operation using them is attempted. IPv6 addresses are normally enclosed between '[' and ']'.

The value of this parameter cannot be null (Nothing in Visual Basic).

serverClass

Contains ProgID of the OPC server to read from.

The value of this parameter cannot be null (Nothing in Visual Basic).

itemId

Contains OPC item identifier.

The value of this parameter cannot be null (Nothing in Visual Basic).

dataType

Specifies the data type requested. Passing OpcLabs.BaseLib.ComInterop.VarTypes.Empty will cause the value be returned in server's canonical data type.

Because the OpcLabs.BaseLib.ComInterop.VarType has an implicit conversion from System.Int32 and OpcLabs.BaseLib.ComInterop.VarTypes, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use an integer (representing the numerical value of the COM VARTYPE), or an element of the OpcLabs.BaseLib.ComInterop.VarTypes enumeration (or an allowed combination of OpcLabs.BaseLib.ComInterop.VarTypes flags) in place of this parameter, and the corresponding data type specification will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.BaseLib.ComInterop.VarType.VarType Constructor(Int32) or OpcLabs.BaseLib.ComInterop.VarType.VarType Constructor(VarTypes) constructor instead.

The value of this parameter cannot be null (Nothing in Visual Basic).

valueAge

The age of value you would like to obtain (in milliseconds).

Return Value

The data source (a device, OPC server's cache, or a value from OPC client component memory cache) is dynamically determined based on the valueAge argument.

This is an extension method (info: C#, VB.NET). In languages that have support for extensions methods (such as C# and VB.NET), you can use the extension method as if it were a regular method on the object that is its first parameter. In other languages (such as with Python.NET), you will call the extension as a static method, and pass it the object on which it acts as its first parameter.

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows