Examples - OPC XML-DA

Example with single item:

.NET

C#
VB.NET

// This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
//
// 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 OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess.Xml
{
    class PullItemChanged
    {
        public static void Main1Xml()
        {
            // Instantiate the client object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyDAClient { PullItemChangedQueueCapacity = 1000 };

            Console.WriteLine("Subscribing item changes...");
            client.SubscribeItem(
                "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx",
                "Dynamic/Analog Types/Int",
                1000,
                state: null);

            Console.WriteLine("Processing item changes for 1 minute...");
            int endTick = Environment.TickCount + 60 * 1000;
            do
            {
                EasyDAItemChangedEventArgs eventArgs = client.PullItemChanged(2 * 1000);
                if (!(eventArgs is null))
                    // Handle the notification event
                    Console.WriteLine(eventArgs);
            } while (Environment.TickCount < endTick);

            Console.WriteLine("Unsubscribing item changes...");
            client.UnsubscribeAllItems();

            Console.WriteLine("Finished.");
        }
    }
}

' This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
'
' 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 OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess.Xml
    Partial Friend Class PullItemChanged
        Public Shared Sub Main1Xml()
            ' In order to use event pull, you must set a non-zero queue capacity upfront.
            Dim client = New EasyDAClient() With {.PullItemChangedQueueCapacity = 1000}

            Console.WriteLine("Subscribing item changes...")
            client.SubscribeItem(
                    "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx",
                    "Dynamic/Analog Types/Int",
                    1000,
                    state:=Nothing)

            Console.WriteLine("Processing item changes for 1 minute...")
            Dim endTick As Integer = Environment.TickCount + 60 * 1000
            Do
                Dim eventArgs As EasyDAItemChangedEventArgs = client.PullItemChanged(2 * 1000)
                If Not eventArgs Is Nothing Then
                    ' Handle the notification event
                    Console.WriteLine(eventArgs)
                End If
            Loop While Environment.TickCount < endTick

            Console.WriteLine("Unsubscribing item changes...")
            client.UnsubscribeAllItems()

            Console.WriteLine("Finished.")
        End Sub
    End Class
End Namespace

COM

// This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in Object Pascal (Delphi) on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-OP .
// 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.

class procedure PullItemChanged.MainXml;
var
  Arguments: OleVariant;
  Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
  EndTick: Cardinal;
  EventArgs: _EasyDAItemChangedEventArgs;
  ItemSubscriptionArguments1: _EasyDAItemSubscriptionArguments;
begin
  ItemSubscriptionArguments1 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments1.ServerDescriptor.UrlString := 'http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx';
  ItemSubscriptionArguments1.ItemDescriptor.ItemID := 'Dynamic/Analog Types/Int';
  ItemSubscriptionArguments1.GroupParameters.RequestedUpdateRate := 1000;

  Arguments := VarArrayCreate([0, 0], varVariant);
  Arguments[0] := ItemSubscriptionArguments1;

  // Instantiate the client object
  Client := CoEasyDAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullItemChangedQueueCapacity := 1000;

  WriteLn('Subscribing item changes...');
  Client.SubscribeMultipleItems(Arguments);

  WriteLn('Processing item changes for 1 minute...');
  EndTick := Ticks + 60*1000;
  while Ticks < EndTick do
  begin
    EventArgs := Client.PullItemChanged(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      WriteLn(EventArgs.ToString);
  end;

  WriteLn('Unsubscribing item changes...');
  Client.UnsubscribeAllItems;

  WriteLn('Finished.');
end;

// This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in PHP on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-PHP .
// 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.

$ItemSubscriptionArguments1 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments");
$ItemSubscriptionArguments1->ServerDescriptor->UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx";
$ItemSubscriptionArguments1->ItemDescriptor->ItemID = "Dynamic/Analog Types/Int";
$ItemSubscriptionArguments1->GroupParameters->RequestedUpdateRate = 1000;

$arguments[0] = $ItemSubscriptionArguments1;

// Instantiate the client object.
$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
// In order to use event pull, you must set a non-zero queue capacity upfront.
$Client->PullItemChangedQueueCapacity = 1000;

print "Subscribing item changes...\n";
$Client->SubscribeMultipleItems($arguments);

print "Processing item changed events for 1 minute...\n";
$endTime = time() + 60;
do {
    $EventArgs = $Client->PullItemChanged(2*1000);
    if (!is_null($EventArgs)) {
        // Handle the notification event
        print $EventArgs->ToString();
        print "\n";
    }
} while (time() < $endTime);

Rem This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
Rem
REM Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
REM OPC client and subscriber examples in Visual Basic on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VB .
REM Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
REM a commercial license in order to use Online Forums, and we reply to every post.

Private Sub PullItemChanged_MainXml_Command_Click()
    OutputText = ""
    
    Dim eventArgs As EasyDAItemChangedEventArgs
    
    Dim ItemSubscriptionArguments1 As New EasyDAItemSubscriptionArguments
    ItemSubscriptionArguments1.serverDescriptor.UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx"
    ItemSubscriptionArguments1.ItemDescriptor.ItemId = "Dynamic/Analog Types/Int"
    ItemSubscriptionArguments1.GroupParameters.RequestedUpdateRate = 1000
    
    Dim arguments(0) As Variant
    Set arguments(0) = ItemSubscriptionArguments1


    ' Instantiate the client object
    Dim client As New EasyDAClient
    
    ' In order to use event pull, you must set a non-zero queue capacity upfront.
    client.PullItemChangedQueueCapacity = 1000
    
    OutputText = OutputText & "Subscribing item changes..." & vbCrLf
    Call client.SubscribeMultipleItems(arguments)
    
    OutputText = OutputText & "Processing item changes for 1 minute..." & vbCrLf
    Dim endTick As Long
    endTick = GetTickCount + 60000
    While GetTickCount < endTick
        Set eventArgs = client.PullItemChanged(2 * 1000)
        If Not eventArgs Is Nothing Then
            ' Handle the notification event
            OutputText = OutputText & eventArgs & vbCrLf
        End If
    Wend
    
    OutputText = OutputText & "Unsubscribing item changes..." & vbCrLf
    client.UnsubscribeAllItems

    OutputText = OutputText & "Finished." & vbCrLf
End Sub

Rem This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Dim ItemSubscriptionArguments1: Set ItemSubscriptionArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments")
ItemSubscriptionArguments1.ServerDescriptor.UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx"
ItemSubscriptionArguments1.ItemDescriptor.ItemID = "Dynamic/Analog Types/Int"
ItemSubscriptionArguments1.GroupParameters.RequestedUpdateRate = 1000

Dim arguments(0)
Set arguments(0) = ItemSubscriptionArguments1

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
' In order to use event pull, you must set a non-zero queue capacity upfront.
Client.PullItemChangedQueueCapacity = 1000

WScript.Echo "Subscribing item changes..."
Client.SubscribeMultipleItems arguments

WScript.Echo "Processing item changes for 1 minute..."
Dim endTime: endTime = Now() + 60*(1/24/60/60)
Do
    Dim EventArgs: Set EventArgs = Client.PullItemChanged(2*1000)
    If Not (EventArgs Is Nothing) Then
        ' Handle the notification event
        WScript.Echo EventArgs
    End If    
Loop While Now() < endTime

WScript.Echo "Unsubscribing item changes..."
Client.UnsubscribeAllItems

WScript.Echo "Finished."

Python

Python (.NET)

# This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.
#
# 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 import *
from OpcLabs.EasyOpc.DataAccess import *


# Instantiate the client object
client = EasyDAClient()
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')
IEasyDAClientExtension.SubscribeItem(client,
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    DAItemDescriptor('Dynamic/Analog Types/Int'),
    DAGroupParameters(1000),
    None) # state

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = IEasyDAClientExtension.PullItemChanged(client, 2*1000)
    if eventArgs is not None:
        # Handle the notification event
        print(eventArgs)

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

Example with multiple items:

COM

Python (COM)

# This example shows how to subscribe to changes of multiple OPC XML-DA items and obtain the item changed events by pulling them.
#
# The Python for Windows (pywin32) extensions package is needed. Install it using "pip install pypiwin32".
# CAUTION: We now recommend using Python.NET package instead. Full set of examples with Python.NET is available!
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
import time
import win32com.client

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient') 
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')

itemSubscriptionArguments1 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments1.ServerDescriptor.UrlString = 'http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'
itemSubscriptionArguments1.ItemDescriptor.ItemID = 'Dynamic/Analog Types/Double'
itemSubscriptionArguments1.GroupParameters.RequestedUpdateRate = 1000

itemSubscriptionArguments2 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments2.ServerDescriptor.UrlString = 'http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'
itemSubscriptionArguments2.ItemDescriptor.ItemID = 'Dynamic/Analog Types/Double[]'
itemSubscriptionArguments2.GroupParameters.RequestedUpdateRate = 1000

itemSubscriptionArguments3 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments3.ServerDescriptor.UrlString = 'http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'
itemSubscriptionArguments3.ItemDescriptor.ItemID = 'Dynamic/Analog Types/Int'
itemSubscriptionArguments3.GroupParameters.RequestedUpdateRate = 1000

# Intentionally specifying an unknown item here, to demonstrate its behavior.
itemSubscriptionArguments4 = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.OperationModel.EasyDAItemSubscriptionArguments')
itemSubscriptionArguments4.ServerDescriptor.UrlString = 'http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'
itemSubscriptionArguments4.ItemDescriptor.ItemID = 'SomeUnknownItem'
itemSubscriptionArguments4.GroupParameters.RequestedUpdateRate = 1000

arguments = [
    itemSubscriptionArguments1,
    itemSubscriptionArguments2,
    itemSubscriptionArguments3,
    itemSubscriptionArguments4,
    ]
client.SubscribeMultipleItems(arguments)

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = client.PullItemChanged(2*1000)
    if eventArgs is not None:
        # Handle the notification event
        if (eventArgs.Succeeded):
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq, sep='')
        else:
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief, sep='')

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

Python

Python (.NET)

# This example shows how to subscribe to changes of multiple OPC XML-DA items and obtain the item changed events by pulling them.
#
# 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 import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *


# Instantiate the client object
client = EasyDAClient()
# In order to use event pull, you must set a non-zero queue capacity upfront.
client.PullItemChangedQueueCapacity = 1000

print('Subscribing item changes...')

itemSubscriptionArguments1 = EasyDAItemSubscriptionArguments(
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    DAItemDescriptor('Dynamic/Analog Types/Double'),
    DAGroupParameters(1000),
    None)

itemSubscriptionArguments2 = EasyDAItemSubscriptionArguments(
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    DAItemDescriptor('Dynamic/Analog Types/Double[]'),
    DAGroupParameters(1000),
    None)

itemSubscriptionArguments3 = EasyDAItemSubscriptionArguments(
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    DAItemDescriptor('Dynamic/Analog Types/Int'),
    DAGroupParameters(1000),
    None)

# Intentionally specifying an unknown item here, to demonstrate its behavior.
itemSubscriptionArguments4 = EasyDAItemSubscriptionArguments(
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    DAItemDescriptor('SomeUnknownItem'),
    DAGroupParameters(1000),
    None)

client.SubscribeMultipleItems([
    itemSubscriptionArguments1,
    itemSubscriptionArguments2,
    itemSubscriptionArguments3,
    itemSubscriptionArguments4,
    ])

print('Processing item changes for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = IEasyDAClientExtension.PullItemChanged(client, 2*1000)
    if eventArgs is not None:
        # Handle the notification event
        if (eventArgs.Succeeded):
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq, sep='')
        else:
            print(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief, sep='')

print('Unsubscribing item changes...')
client.UnsubscribeAllItems()

print('Finished.')

QuickOPC supports OPC XML-DA also on Linux and macOS.

Examples - Client OPC Data Access

Examples - OPC Data Access - Event pull

Concepts

Subscribing to OPC Classic Items

Event Pull Mechanism