Subscribe to OPC item using an object that holds all necessary arguments, including an optional callback.
Syntax
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).
- easyItemSubscriptionArguments
- Arguments specifying how to subscribe to an OPC DA item.
The value of this parameter cannot be null
(Nothing
in Visual Basic).
Return Value
The method returns an integer handle that uniquely identifies the item subscription.
Exceptions
Exception | Description |
System.ArgumentNullException |
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. |
Example
// Hooking up events and receiving OPC item changes.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.
using System;
using System.Threading;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;
namespace DocExamples.DataAccess._EasyDAClient
{
partial class SubscribeItem
{
public static void Main1()
{
// Instantiate the client object.
using (var client = new EasyDAClient())
{
var eventHandler = new EasyDAItemChangedEventHandler(client_ItemChanged);
client.ItemChanged += eventHandler;
Console.WriteLine("Subscribing item...");
client.SubscribeItem("", "OPCLabs.KitServer.2", "Demo.Ramp", 200);
Console.WriteLine("Process item change notifications for 30 seconds...");
Thread.Sleep(30 * 1000);
Console.WriteLine("Unsubscribing all items...");
client.UnsubscribeAllItems();
client.ItemChanged -= eventHandler;
}
Console.WriteLine("Finished.");
}
static void client_ItemChanged(object sender, EasyDAItemChangedEventArgs e)
{
if (e.Succeeded)
Console.WriteLine(e.Vtq);
else
Console.WriteLine($"*** Failure: {e.ErrorMessageBrief}");
}
}
}
# Hooking up events and receiving OPC item changes.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in PowerShell on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-PowerShell .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
#requires -Version 5.1
using namespace OpcLabs.EasyOpc.DataAccess
# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"
# Instantiate the client object.
$client = New-Object EasyDAClient
# Item changed event handler
Register-ObjectEvent -InputObject $client -EventName ItemChanged -Action {
if ($EventArgs.Succeeded) {
Write-Host $EventArgs.Vtq
}
else {
Write-Host "*** Failure: $($EventArgs.ErrorMessageBrief)"
}
}
Write-Host "Subscribing item..."
[IEasyDAClientExtension]::SubscribeItem($client, "", "OPCLabs.KitServer.2", "Demo.Ramp", 200)
Write-Host "Processing item changes for 30 seconds..."
$stopwatch = [System.Diagnostics.Stopwatch]::StartNew()
while ($stopwatch.Elapsed.TotalSeconds -lt 30) {
Start-Sleep -Seconds 1
}
Write-Host "Unsubscribing items..."
$client.UnsubscribeAllItems()
Write-Host "Finished."
' Hooking up events and receiving OPC item changes.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.
Imports System.Threading
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel
Namespace DataAccess._EasyDAClient
Partial Friend Class SubscribeItem
Shared Sub Main1()
Using client = New EasyDAClient()
Dim eventHandler = New EasyDAItemChangedEventHandler(AddressOf client_ItemChanged)
AddHandler client.ItemChanged, eventHandler
Console.WriteLine("Subscribing item...")
client.SubscribeItem("", "OPCLabs.KitServer.2", "Demo.Ramp", 200)
Thread.Sleep(30 * 1000)
client.UnsubscribeAllItems()
RemoveHandler client.ItemChanged, eventHandler
End Using
End Sub
Private Shared Sub client_ItemChanged(sender As Object, e As EasyDAItemChangedEventArgs)
If e.Succeeded Then
Console.WriteLine(e.Vtq)
Else
Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief)
End If
End Sub
End Class
End Namespace
# Hooking up events and receiving OPC item changes.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time
# Import .NET namespaces.
from OpcLabs.EasyOpc.DataAccess import *
# Item changed event handler.
def itemChanged(sender, e):
if e.Succeeded:
print(e.Vtq)
else:
print('*** Failure: ', e.ErrorMessageBrief, sep='')
# Instantiate the client object.
client = EasyDAClient()
client.ItemChanged += itemChanged
print('Subscribing item changes...')
IEasyDAClientExtension.SubscribeItem(client, '', 'OPCLabs.KitServer.2', 'Demo.Ramp', 200)
print('Processing item change notifications for 30 seconds...')
time.sleep(30)
print('Unsubscribing all items...')
client.UnsubscribeAllItems()
client.ItemChanged -= itemChanged
print('Finished.')
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