OPC Studio User's Guide and Reference
SubscribeItem(IEasyDAClient,String,String,String,Int32,Object) Method



OpcLabs.EasyOpcClassicCore Assembly > OpcLabs.EasyOpc.DataAccess Namespace > IEasyDAClientExtension Class > SubscribeItem Method : SubscribeItem(IEasyDAClient,String,String,String,Int32,Object) Method
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).

Name of the machine (empty string for local computer).

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).

Contains ProgID of the OPC server.

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

ID of the item that will be subscribed to.

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

How often should the updates be received (number of milliseconds)
The state object (can be any object supplied by your code); available in event notifications.

The value of this parameter can be null (Nothing in Visual Basic).

Subscribe to OPC item. Specify machine name, server class, item ID, requested update rate, and a state object.
Syntax
'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Function SubscribeItem( _
   ByVal client As IEasyDAClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String, _
   ByVal requestedUpdateRate As Integer, _
   ByVal state As Object _
) As Integer
'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim requestedUpdateRate As Integer
Dim state As Object
Dim value As Integer
 
value = IEasyDAClientExtension.SubscribeItem(client, machineName, serverClass, itemId, requestedUpdateRate, state)

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 (empty string for local computer).

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.

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

itemId
ID of the item that will be subscribed to.

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

requestedUpdateRate
How often should the updates be received (number of milliseconds)
state
The state object (can be any object supplied by your code); available in event notifications.

The value of this parameter can be null (Nothing in Visual Basic).

Return Value

The method returns an integer handle that uniquely identifies the item subscription.
Exceptions
ExceptionDescription

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

The value of an argument is outside the allowable range of values as defined by the invoked method.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

Remarks

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.

Requirements

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

See Also