QuickOPC User's Guide and Reference
Event Pull Mechanism
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Event pull mechanism is an alternative to the traditional delivery mechanism of notifications through event handlers. Setting up event handlers, and properly handling events, is difficult or impossible in some (especially COM-based) tools (e.g. Python) or in some environments (e.g. applications running under Web server). In COM, unless taken care of already by the tool, the developer must also assure that (in an STA model) Windows messages are being pumped by the application.

Note: This feature should only be used when the traditional event delivery approach is not feasible. It is unlikely that you will need to use the event pull mechanism in C# or VB.NET (except maybe for server-side of certain Web apps and Web services).

Event pull mechanism replaces the event handlers by methods that allow the developer to obtain a next available notification from an internally provided queue. Events can then be handled by a loop that calls the “pull” method and processes the notifications. In order to maintain reasonable performance, a so-called long poll approach is used: The method only returns after a notification becomes available, or a specified timeout elapses. Note that the event pull concept is strictly confined to how the QuickOPC exchanges notifications with the enclosing application, and is not related to how QuickOPC communicates with OPC servers.

For each event XXXX, by convention, two methods for event pull mechanism are provided: A PullXXXX method, which allows to retrieve a single notification, and a PullMultipleXXXX method, which allows to retrieve multiple notifications, if they are available. Although currently is no significant performance difference between the two methods, it is recommended that your code uses the PullMultipleXXXX methods, because it may bring performance benefits in the future.

The following table shows the traditional events, and their corresponding methods for event pull:

Type Event Pull method PullMultiple method
EasyDAClient ItemChanged PullItemChanged PullMultipleItemChanges
EasyAEClient Notification PullNotification PullMultipleNotifications
EasyUAClient DataChangeNotification PullDataChangeNotification PullMultipleDataChangeNotifications
EventNotification PullEventNotification PullMultipleEventNotifications
EasyUASubscriber Class DataSetMessage Event PullDataSetMessage Method PullMultipleDataSetMessages Method
ResolverAccess Event PullResolverAccess Method PullMultipleResolverAccesses Method
IEasyUAClientConnectionMonitoring Interface ServerConditionChanged PullServerConditionChanged PullMultipleServerConditionChanges

Each PullXXXX or PullMultipleXXXX method takes an argument that specifies a timeout (in milliseconds). When a notification is available, the methods returns it immediately, and return a non-null object containing the event arguments (or an array of such event arguments, for PullMultipleXXXX). If no notifications are available during the specified period (timeout), the methods returns after the period elapses, but the return value is a null reference.

After your code receives a non-null event arguments object, it can process it as it would do in a traditional event handler.

You will probably be calling the PullXXXX or PullMultipleXXXX method in a loop with some termination condition. Specify a timeout that will allow the loop to react to the termination condition quickly enough. You should not, however, use very low (or zero) timeouts in such a loop, because that would lead to unnecessary high CPU consumption.

In order to use the event pull mechanism, your code needs to set up a queue with a fixed capacity upfront. This is done by setting a corresponding property in the EasyXXClient object. By convention, for an event named XXXX, the property name is PullXXXXQueueCapacity. For example, set the EasyUAClient.PullDataChangeNotificationQueueCapacity property to allocate a queue for OPC UA data change notifications.

If you do not set the queue capacity to a positive (non-zero) value, and attempt to use the event pull mechanism, the PullXXXX or PullMultipleXXXX method will throw an InvalidOperationException.

Examples

Examples for OPC Data Access:

Example with single item:

.NET

// This example shows how to subscribe to item changes and obtain the events by pulling them.

using System;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class PullItemChanged
    {
        public static void Main1()
        {
            // 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("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

            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.");
        }
    }
}

COM

// This example shows how to subscribe to item changes and obtain the events by pulling them.

var Client = new ActiveXObject("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.SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

WScript.Echo("Processing item changes for 1 minute...");
var endTime = new Date().getTime() + 60*1000
do {
    var EventArgs = Client.PullItemChanged(2*1000);
    if (EventArgs !== null) {
        //  Handle the notification event
        WScript.Echo(EventArgs);
    }
} while(new Date().getTime() < endTime);

WScript.Echo("Unsubscribing item changes...");
Client.UnsubscribeAllItems();

WScript.Echo("Finished.");

Example with multiple items:

.NET

// This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.

using System;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class PullItemChanged
    {
        public static void MultipleItems()
        {
            // 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.SubscribeMultipleItems(
                new[] {
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, null),
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000, null),
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, null),
                    // Intentionally specifying an unknown item here, to demonstrate its behavior.
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "SomeUnknownItem", 1000, 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
                    if (eventArgs.Succeeded)
                        Console.WriteLine($"{eventArgs.Arguments.ItemDescriptor.ItemId}: {eventArgs.Vtq}");
                    else
                        Console.WriteLine($"{eventArgs.Arguments.ItemDescriptor.ItemId} *** Failure: {eventArgs.ErrorMessageBrief}");
            } while (Environment.TickCount < endTick);

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

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

COM

// This example shows how to subscribe to changes of multiple items and obtain the item changed events by pulling them.

class procedure PullItemChanged.MultipleItems;
var
  Arguments: OleVariant;
  Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
  EndTick: Cardinal;
  EventArgs: _EasyDAItemChangedEventArgs;
  HandleArray: OleVariant;
  ItemSubscriptionArguments1: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments2: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments3: _EasyDAItemSubscriptionArguments;
  ItemSubscriptionArguments4: _EasyDAItemSubscriptionArguments;
begin
  ItemSubscriptionArguments1 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments1.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments1.ItemDescriptor.ItemID := 'Simulation.Random';
  ItemSubscriptionArguments1.GroupParameters.RequestedUpdateRate := 1000;

  ItemSubscriptionArguments2 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments2.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments2.ItemDescriptor.ItemID := 'Trends.Ramp (1 min)';
  ItemSubscriptionArguments2.GroupParameters.RequestedUpdateRate := 1000;

  ItemSubscriptionArguments3 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments3.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments3.ItemDescriptor.ItemID := 'Trends.Sine (1 min)';
  ItemSubscriptionArguments3.GroupParameters.RequestedUpdateRate := 1000;

  // Intentionally specifying an unknown item here, to demonstrate its behavior.
  ItemSubscriptionArguments4 := CoEasyDAItemSubscriptionArguments.Create;
  ItemSubscriptionArguments4.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ItemSubscriptionArguments4.ItemDescriptor.ItemID := 'SomeUnknownItem';
  ItemSubscriptionArguments4.GroupParameters.RequestedUpdateRate := 1000;

  Arguments := VarArrayCreate([0, 3], varVariant);
  Arguments[0] := ItemSubscriptionArguments1;
  Arguments[1] := ItemSubscriptionArguments2;
  Arguments[2] := ItemSubscriptionArguments3;
  Arguments[3] := ItemSubscriptionArguments4;

  // 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...');
  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(
    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
      if eventArgs.Succeeded then
        WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ': ', eventArgs.Vtq.ToString)
      else
        WriteLn(eventArgs.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', eventArgs.ErrorMessageBrief);
  end;

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

  VarClear(HandleArray);
  VarClear(Arguments);

  WriteLn('Finished.');
end;

Examples for OPC Alarms&Events:

.NET

// This example shows how to subscribe to events and obtain the notification events by pulling them.

using System;
using OpcLabs.EasyOpc.AlarmsAndEvents;
using OpcLabs.EasyOpc.AlarmsAndEvents.OperationModel;

namespace DocExamples.AlarmsAndEvents._EasyAEClient
{
    class PullNotification
    {
        public static void Main1()
        {
            // Instantiate the client object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            using (var client = new EasyAEClient { PullNotificationQueueCapacity = 1000 })
            {
                Console.WriteLine("Subscribing events...");
                int handle = client.SubscribeEvents("", "OPCLabs.KitEventServer.2", 1000);

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

                Console.WriteLine("Unsubscribing events...");
                client.UnsubscribeEvents(handle);

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

COM

// This example shows how to subscribe to events and obtain the notification events by pulling them.

class procedure PullNotification.Main;
var
  Client: OpcLabs_EasyOpcClassic_TLB._EasyAEClient;
  EndTick: Cardinal;
  EventArgs: _EasyAENotificationEventArgs;
  Handle: Integer;
  ServerDescriptor: _ServerDescriptor;
  State: OleVariant;
  SubscriptionParameters: _AESubscriptionParameters;
begin
  ServerDescriptor := CoServerDescriptor.Create;
  ServerDescriptor.ServerClass := 'OPCLabs.KitEventServer.2';

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

  WriteLn('Subscribing events...');
  SubscriptionParameters := CoAESubscriptionParameters.Create;
  SubscriptionParameters.NotificationRate := 1000;
  Handle := Client.SubscribeEvents(ServerDescriptor, SubscriptionParameters, true, State);

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

  WriteLn('Unsubscribing events...');
  Client.UnsubscribeEvents(Handle);

  WriteLn('Finished.');
end;

 

Examples for OPC XML-DA:

Example with single item:

// This example shows how to subscribe to OPC XML-DA item changes and obtain the events by pulling them.

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.");
        }
    }
}

Example with multiple items:

.NET

# This example shows how to subscribe to changes of multiple OPC XML-DA items and obtain the item changed events by pulling them.

# 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.')

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

Examples for OPC UA (Data):

.NET

// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClient
{
    class PullDataChangeNotification
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyUAClient { PullDataChangeNotificationQueueCapacity = 1000 };

            Console.WriteLine("Subscribing...");
            client.SubscribeDataChange(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853", 1000);

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

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();
        }
    }
}

COM

// This example shows how to subscribe to changes of a single monitored item, pull events, and display each change.

class procedure PullDataChangeNotification.Main;
var
  Client: EasyUAClient;
  EndTick: Cardinal;
  EventArgs: _EasyUADataChangeNotificationEventArgs;
begin
  // Instantiate the client object
  Client := CoEasyUAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullDataChangeNotificationQueueCapacity := 1000;

  WriteLn('Subscribing...');
  Client.SubscribeDataChange(
    //'http://opcua.demo-this.com:51211/UA/SampleServer',
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer',
    'nsu=http://test.org/UA/Data/ ;i=10853',
    1000);

  WriteLn('Processing data change events for 1 minute...');
  EndTick := GetTickCount + 60*1000;
  while GetTickCount < EndTick do
  begin
    EventArgs := Client.PullDataChangeNotification(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      WriteLn(EventArgs.ToString);
  end;

  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;

  WriteLn('Finished.');
end;

Examples for OPC UA (Alarms & Conditions):

.NET

// This example shows how to subscribe to event notifications, pull events, and display each incoming event.

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.AddressSpace.Standard;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples.AlarmsAndConditions
{
    class PullEventNotification
    {
        public static void Main1()
        {
            // Define which server we will work with.
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";

            // Instantiate the client object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var client = new EasyUAClient { PullEventNotificationQueueCapacity = 1000 };

            Console.WriteLine("Subscribing...");
            client.SubscribeEvent(endpointDescriptor, UAObjectIds.Server, 1000);

            Console.WriteLine("Processing event notifications for 30 seconds...");
            int endTick = Environment.TickCount + 30 * 1000;
            do
            {
                EasyUAEventNotificationEventArgs eventArgs = client.PullEventNotification(2 * 1000);
                if (!(eventArgs is null))
                    // Handle the notification event.
                    Console.WriteLine(eventArgs);
            } while (Environment.TickCount < endTick);

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();

            Console.WriteLine("Finished.");
        }

        // Example output (truncated):
        //Subscribing...
        //Processing event notifications for 30 seconds...
        //[] Success
        //[] Success; Refresh; RefreshInitiated
        //[] Success; Refresh; (10 field results) [EastTank] 100! "The dialog was activated" @9/10/2019 8:08:23 PM
        //[] Success; Refresh; (10 field results) [EastTank] 500! "The alarm was acknoweledged." @10/14/2019 4:00:13 PM
        //[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm was acknoweledged." @11/9/2019 9:56:23 AM
        //[] Success; Refresh; (10 field results) [EastTank] 500! "The alarm was acknoweledged." @10/14/2019 4:00:17 PM
        //[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm severity has increased." @9/10/2019 8:09:07 PM
        //[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm severity has increased." @9/10/2019 8:10:09 PM
        //[] Success; Refresh; (10 field results) [NorthMotor] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
        //[] Success; Refresh; (10 field results) [NorthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:02 PM
        //[] Success; Refresh; (10 field results) [NorthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:16 PM
        //[] Success; Refresh; (10 field results) [NorthMotor] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
        //[] Success; Refresh; (10 field results) [NorthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:11 PM
        //[] Success; Refresh; (10 field results) [NorthMotor] 100! "The alarm severity has increased." @9/10/2019 8:10:19 PM
        //[] Success; Refresh; (10 field results) [WestTank] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
        //[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm was acknoweledged." @10/14/2019 4:00:12 PM
        //[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
        //[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm was acknoweledged." @10/14/2019 4:00:04 PM
        //[] Success; Refresh; (10 field results) [WestTank] 100! "The alarm severity has increased." @9/10/2019 8:08:58 PM
        //[] Success; Refresh; (10 field results) [WestTank] 100! "The alarm severity has increased." @9/10/2019 8:09:48 PM
        //[] Success; Refresh; (10 field results) [SouthMotor] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
        //[] Success; Refresh; (10 field results) [SouthMotor] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
        //[] Success; Refresh; (10 field results) [SouthMotor] 700! "The alarm was acknoweledged." @10/14/2019 4:00:21 PM
        //[] Success; Refresh; (10 field results) [SouthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:03 PM
        //[] Success; Refresh; (10 field results) [SouthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:02 PM
        //[] Success; Refresh; (10 field results) [SouthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:59 PM
        //[] Success; Refresh; RefreshComplete
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:43 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:43 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:44 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:44 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:45 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:45 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:46 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:46 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:47 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:47 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:48 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:48 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:49 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:49 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:50 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:50 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:51 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:51 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:52 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:52 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:53 AM
        //[] Success; (10 field results) [NorthMotor] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:53 AM
        //[] Success; (10 field results) [WestTank] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
        //[] Success; (10 field results) [SouthMotor] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:54 AM
        //[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:54 AM
        //[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:55 AM
        //...
    }
}

COM

// This example shows how to subscribe to event notifications, pull events, and display each incoming event.

class procedure PullEventNotification.Main;
var
  Client: OpcLabs_EasyOpcUA_TLB._EasyUAClient;
  EndTick: Cardinal;
  EventArgs: _EasyUAEventNotificationEventArgs;
begin
  // Instantiate the client object and hook events
  Client := CoEasyUAClient.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Client.PullEventNotificationQueueCapacity := 1000;

  WriteLn('Subscribing...');
  Client.SubscribeEvent(
    'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer',
    'nsu=http://opcfoundation.org/UA/;i=2253',  // UAObjectIds.Server
    1000);

  WriteLn('Processing event notifications for 30 seconds...');
  EndTick := Ticks + 30*1000;
  while Ticks < EndTick do
  begin
    EventArgs := Client.PullEventNotification(2*1000);
    if EventArgs <> nil then
      // Handle the notification event
      WriteLn(EventArgs.ToString);
  end;

  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;

  WriteLn('Finished.');
end;

// Example output (truncated):
//Subscribing...
//Processing event notifications for 30 seconds...
//[] Success
//[] Success; Refresh; RefreshInitiated
//[] Success; Refresh; (10 field results) [EastTank] 100! "The dialog was activated" @9/10/2019 8:08:23 PM
//[] Success; Refresh; (10 field results) [EastTank] 500! "The alarm was acknoweledged." @10/14/2019 4:00:13 PM
//[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm was acknoweledged." @11/9/2019 9:56:23 AM
//[] Success; Refresh; (10 field results) [EastTank] 500! "The alarm was acknoweledged." @10/14/2019 4:00:17 PM
//[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm severity has increased." @9/10/2019 8:09:07 PM
//[] Success; Refresh; (10 field results) [EastTank] 100! "The alarm severity has increased." @9/10/2019 8:10:09 PM
//[] Success; Refresh; (10 field results) [NorthMotor] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
//[] Success; Refresh; (10 field results) [NorthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:02 PM
//[] Success; Refresh; (10 field results) [NorthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:16 PM
//[] Success; Refresh; (10 field results) [NorthMotor] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
//[] Success; Refresh; (10 field results) [NorthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:11 PM
//[] Success; Refresh; (10 field results) [NorthMotor] 100! "The alarm severity has increased." @9/10/2019 8:10:19 PM
//[] Success; Refresh; (10 field results) [WestTank] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
//[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm was acknoweledged." @10/14/2019 4:00:12 PM
//[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
//[] Success; Refresh; (10 field results) [WestTank] 300! "The alarm was acknoweledged." @10/14/2019 4:00:04 PM
//[] Success; Refresh; (10 field results) [WestTank] 100! "The alarm severity has increased." @9/10/2019 8:08:58 PM
//[] Success; Refresh; (10 field results) [WestTank] 100! "The alarm severity has increased." @9/10/2019 8:09:48 PM
//[] Success; Refresh; (10 field results) [SouthMotor] 100! "The dialog was activated" @9/10/2019 8:08:25 PM
//[] Success; Refresh; (10 field results) [SouthMotor] 300! "The alarm severity has increased." @11/9/2019 10:29:42 AM
//[] Success; Refresh; (10 field results) [SouthMotor] 700! "The alarm was acknoweledged." @10/14/2019 4:00:21 PM
//[] Success; Refresh; (10 field results) [SouthMotor] 500! "The alarm was acknoweledged." @10/14/2019 4:00:03 PM
//[] Success; Refresh; (10 field results) [SouthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:02 PM
//[] Success; Refresh; (10 field results) [SouthMotor] 100! "The alarm severity has increased." @9/10/2019 8:09:59 PM
//[] Success; Refresh; RefreshComplete
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:43 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:43 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:44 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:44 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:45 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:45 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:46 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:46 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:47 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:47 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:48 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:48 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:49 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:49 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:50 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:50 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:51 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:51 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:52 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:52 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:53 AM
//[] Success; (10 field results) [NorthMotor] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:53 AM
//[] Success; (10 field results) [WestTank] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
//[] Success; (10 field results) [SouthMotor] 500! "The alarm severity has increased." @11/9/2019 10:29:53 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:54 AM
//[] Success; (10 field results) [Internal] 500! "Events Raised" @11/9/2019 10:29:54 AM
//[] Success; (10 field results) [Internal] 500! "Raising Events" @11/9/2019 10:29:55 AM
//...

 

Examples for OPC UA PubSub:

The example below subscribes to all dataset messages on an OPC-UA PubSub connection with UDP UADP mapping. The connection is specified by its physical parameters, using the scheme name "opc.udp" and the IP address of the multicast group to listen on.

.NET

// This example shows how to subscribe to all dataset messages on an OPC-UA PubSub connection, and pull events, and display
// the incoming datasets.
//
// In order to produce network messages for this example, run the UADemoPublisher tool. For documentation, see
// http://kb.opclabs.com/UADemoPublisher_Basics . In some cases, you may have to specify the interface name to be used.

using System;
using System.Collections.Generic;
using System.Threading;
using OpcLabs.EasyOpc.UA.PubSub;
using OpcLabs.EasyOpc.UA.PubSub.OperationModel;

namespace UADocExamples.PubSub._EasyUASubscriber
{
    class PullDataSetMessage
    {
        public static void Main1()
        {
            // Define the PubSub connection we will work with. Uses implicit conversion from a string.
            UAPubSubConnectionDescriptor pubSubConnectionDescriptor = "opc.udp://239.0.0.1";
            // In some cases you may have to set the interface (network adapter) name that needs to be used, similarly to
            // the statement below. Your actual interface name may differ, of course.
            //pubSubConnectionDescriptor.ResourceAddress.InterfaceName = "Ethernet";

            // Instantiate the subscriber object.
            // In order to use event pull, you must set a non-zero queue capacity upfront.
            var subscriber = new EasyUASubscriber {PullDataSetMessageQueueCapacity = 1000};

            Console.WriteLine("Subscribing...");
            subscriber.SubscribeDataSet(pubSubConnectionDescriptor);

            Console.WriteLine("Processing dataset message events for 20 seconds...");
            int endTick = Environment.TickCount + 20 * 1000;
            do
            {
                EasyUADataSetMessageEventArgs eventArgs = subscriber.PullDataSetMessage(2 * 1000);
                if (!(eventArgs is null))
                {
                    // Display the dataset.
                    if (eventArgs.Succeeded)
                    {
                        // An event with null DataSetData just indicates a successful connection.
                        if (!(eventArgs.DataSetData is null))
                        {
                            Console.WriteLine();
                            Console.WriteLine($"Dataset data: {eventArgs.DataSetData}");
                            foreach (KeyValuePair<string, UADataSetFieldData> pair in eventArgs.DataSetData.FieldDataDictionary)
                                Console.WriteLine(pair);
                        }
                    }
                    else
                    {
                        Console.WriteLine();
                        Console.WriteLine($"*** Failure: {eventArgs.ErrorMessageBrief}");
                    }
                }
            } while (Environment.TickCount < endTick);

            Console.WriteLine("Unsubscribing...");
            subscriber.UnsubscribeAllDataSets();

            Console.WriteLine("Waiting for 1 second...");
            // Unsubscribe operation is asynchronous, messages may still come for a short while.
            Thread.Sleep(1 * 1000);

            Console.WriteLine("Finished.");
        }

        // Example output:
        //
        //Subscribing...
        //Processing dataset message events for 20 seconds...
        //
        //Dataset data: Good; Data; publisher="32", writer=1, class=eae79794-1af7-4f96-8401-4096cd1d8908, fields: 4
        //[#0, True {System.Boolean} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#1, 7945 {System.Int32} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#2, 5246 {System.Int32} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#3, 9/30/2019 11:19:14 AM {System.DateTime} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //
        //Dataset data: Good; Data; publisher="32", writer=3, class=96976b7b-0db7-46c3-a715-0979884b55ae, fields: 100
        //[#0, 45 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#1, 145 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#2, 245 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#3, 345 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#4, 445 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#5, 545 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#6, 645 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#7, 745 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#8, 845 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#9, 945 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //[#10, 1045 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
        //...
    }
}

COM

// This example shows how to subscribe to all dataset messages on an OPC-UA PubSub connection, and pull events, and display
// the incoming datasets.
//
// In order to produce network messages for this example, run the UADemoPublisher tool. For documentation, see
// http://kb.opclabs.com/UADemoPublisher_Basics . In some cases, you may have to specify the interface name to be used.


class procedure PullDataSetMessage.Main1;
var
  ConnectionDescriptor: _UAPubSubConnectionDescriptor;
  Count: Cardinal;
  Element: OleVariant;
  EndTick: Cardinal;
  EventArgs: _EasyUADataSetMessageEventArgs;
  PairEnumerator: IEnumVARIANT;
  SubscribeDataSetArguments: _EasyUASubscribeDataSetArguments;
  Subscriber: OpcLabs_EasyOpcUA_TLB._EasyUASubscriber;
begin
  // Define the PubSub connection we will work with.
  SubscribeDataSetArguments := CoEasyUASubscribeDataSetArguments.Create;
  ConnectionDescriptor := SubscribeDataSetArguments.DataSetSubscriptionDescriptor.ConnectionDescriptor;
  ConnectionDescriptor.ResourceAddress.ResourceDescriptor.UrlString := 'opc.udp://239.0.0.1';
  // In some cases you may have to set the interface (network adapter) name that needs to be used, similarly to
  // the statement below. Your actual interface name may differ, of course.
  // ConnectionDescriptor.ResourceAddress.InterfaceName := 'Ethernet';

  // Instantiate the subscriber object.
  Subscriber := CoEasyUASubscriber.Create;
  // In order to use event pull, you must set a non-zero queue capacity upfront.
  Subscriber.PullDataSetMessageQueueCapacity := 1000;

  WriteLn('Subscribing...');
  Subscriber.SubscribeDataSet(SubscribeDataSetArguments);

  WriteLn('Processing dataset message events for 20 seconds...');
  EndTick := Ticks + 20*1000;
  while Ticks < EndTick do
  begin
    EventArgs := Subscriber.PullDataSetMessage(2*1000);
    if EventArgs <> nil then
      begin
        // Display the dataset.
        if EventArgs.Succeeded then
        begin
          // An event with null DataSetData just indicates a successful connection.
          if EventArgs.DatasetData <> nil then
          begin
            WriteLn;
            WriteLn('Dataset data: ', EventArgs.DatasetData.ToString);
            PairEnumerator := EventArgs.DataSetData.FieldDataDictionary.GetEnumerator;
            while (PairEnumerator.Next(1, Element, Count) = S_OK) do
            begin
              WriteLn(Element.ToString);
            end;
          end;
        end
        else
        begin
          WriteLn;
             WriteLn(' *** Failure: ', EventArgs.ErrorMessageBrief);
        end;
      end;
  end;

  WriteLn('Unsubscribing...');
  Subscriber.UnsubscribeAllDataSets;

  WriteLn('Waiting for 1 second...');
  // Unsubscribe operation is asynchronous, messages may still come for a short while.
  PumpSleep(1*1000);

  WriteLn('Finished.');
end;

// Example output:
//
//Subscribing...
//Processing dataset message events for 20 seconds...
//
//Dataset data: Good; Data; publisher="32", writer=1, class=eae79794-1af7-4f96-8401-4096cd1d8908, fields: 4
//[#0, True {System.Boolean} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#1, 7945 {System.Int32} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#2, 5246 {System.Int32} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#3, 9/30/2019 11:19:14 AM {System.DateTime} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//
//Dataset data: Good; Data; publisher="32", writer=3, class=96976b7b-0db7-46c3-a715-0979884b55ae, fields: 100
//[#0, 45 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#1, 145 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#2, 245 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#3, 345 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#4, 445 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#5, 545 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#6, 645 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#7, 745 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#8, 845 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#9, 945 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//[#10, 1045 {System.Int64} @0001-01-01T00:00:00.000 @@0001-01-01T00:00:00.000; Good]
//...

 

More information

Besides the usual ArgumentException (when your code passes in an improper argument), the InvalidOperationException described above (which also indicates a bug in the code), and system exceptions such OutOfMemoryException, the PullXXXX and PullMultipleXXXX methods can only throw one type of exception, and that is ProcedureCallException. The current implementation does not actually throw this exception type, but future implementations may do so, and we recommend that your code is written in such a way that is ready for that. The ProcedureCallException indicates a failure in the event delivery mechanism (and a likely loss of one or more notifications).

Make sure you always specify a queue capacity that will provide a “buffer” of sufficient length for a difference between the rate of incoming notifications, and the rate your code can consume them. Besides an indication through the event log output (currently in OPC UA only), there is no way to detect queue overflows.

See Also
Simultaneous Operations
Connection handling
Components and Objects
Conventions
Typical Usage
Error Model in imperative programming
Helper Types
OPC UA Client-Server Security
Fundamentals
Imperative Programming Model
Operational Methods Overview
Python (COM) Examples

Knowledge Base

Event Pull Mechanism

Examples - OPC UA PubSub

Examples - OPC UA PubSub - Event pull

Examples - OPC Alarms&Events

Examples - OPC Alarms&Events - Event pull

Examples - OPC Data Access

Examples - OPC Data Access - Event pull

Examples - OPC UA Alarms&Conditions

Examples - OPC UA Alarms&Conditions - Event pull

Examples - OPC Unified Architecture

Examples - OPC Unified Architecture - Event pull of data change notifications
Examples - OPC Unified Architecture - Event pull, subscribing to multiple data change notifications

Examples - OPC XML-DA

Examples - OPC XML-DA - Event pull

 

 

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