QuickOPC User's Guide and Reference
DataChangeNotification Event (EasyUAClientCore)
Example 



View with Navigation Tools
OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA Namespace > EasyUAClientCore Class : DataChangeNotification Event
Raised for every significant change in a subscribed OPC monitored item.
Syntax
'Declaration
 

Public Event DataChangeNotification As EasyUADataChangeNotificationEventHandler
 
'Usage
 

Dim instance As EasyUAClientCore
Dim handler As EasyUADataChangeNotificationEventHandler
 
AddHandler instance.DataChangeNotification, handler
Event Data

The event handler receives an argument of type EasyUADataChangeNotificationEventArgs containing data related to this event. The following EasyUADataChangeNotificationEventArgs properties provide information specific to this event.

PropertyDescription
ArgumentsHolds arguments that were used to subscribe to a monitored item in an OPC-UA server.  
AttributeDataAttribute data: the value of an attribute, together with status code and timestamps.  
DiagnosticsDiagnostics information (such as warnings) assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
DiagnosticsCountCount of diagnostic information elements assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
DiagnosticsSummaryTextual summary of diagnostics information, one message per line. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
ErrorIdGets or sets the error ID of the error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
ErrorMessageGets or sets a message that describes the current exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
ErrorMessageBriefThe first line of the error message. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
ExceptionGets the current exception. Contains null reference when no exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
NormalizedDiagnosticsA normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Diagnostics collection. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
NormalizedExceptionA normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Exception object, or null if there was no error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
StatusInfoStatus information corresponding to the contents of the event arguments.  
SucceededGets indication whether the operation has succeeded. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Example

.NET

.NET

.NET

COM

.NET

.NET

.NET

COM

// This example shows how to subscribe to changes of a single monitored item and display the value of the item with each
// change.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeDataChange
    {
        public static void Overload1()
        {
            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 and hook events.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification;

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

            Console.WriteLine("Processing data change events for 20 seconds...");
            System.Threading.Thread.Sleep(20 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void client_DataChangeNotification(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value.
            if (e.Succeeded)
                Console.WriteLine($"Value: {e.AttributeData.Value}");
            else
                Console.WriteLine($"*** Failure: {e.ErrorMessageBrief}");
        }
    }
}
// This example shows how to subscribe to changes of multiple monitored items and display the value of the monitored item with 
// each change.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeMultipleMonitoredItems
    {
        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 and hook events.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification_Main1;

            Console.WriteLine("Subscribing...");
            client.SubscribeMultipleMonitoredItems(new[]
                {
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10845", 1000),
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10853", 1000),
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10855", 1000)
                });

            Console.WriteLine("Processing monitored item changed events for 10 seconds...");
            System.Threading.Thread.Sleep(10 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void client_DataChangeNotification_Main1(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value.
            if (e.Succeeded)
                Console.WriteLine($"{e.Arguments.NodeDescriptor}: {e.AttributeData.Value}");
            else
                Console.WriteLine($"{e.Arguments.NodeDescriptor} *** Failure: {e.ErrorMessageBrief}");
        }
    }
}
// This example shows how to subscribe to changes of multiple monitored items
// and display each change, identifying the different subscriptions by an
// integer.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeMultipleMonitoredItems
    {
        public static void StateAsInteger()
        {
            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 and hook events.
            var client = new EasyUAClient();
            client.DataChangeNotification += ClientOnDataChangeNotification_StateAsInteger;

            Console.WriteLine("Subscribing...");
            int[] handleArray = client.SubscribeMultipleMonitoredItems(new[]
                {
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10845", 1000)
                        {State = 1},    // An integer we have chosen to identify the subscription
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10853", 1000)
                        {State = 2},    // An integer we have chosen to identify the subscription
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10855", 1000)
                        {State = 3}     // An integer we have chosen to identify the subscription
                });

            for (int i = 0; i < handleArray.Length; i++)
                Console.WriteLine($"handleArray[{i}]: {handleArray[i]}");

            Console.WriteLine("Processing monitored item changed events for 10 seconds...");
            Thread.Sleep(10 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void ClientOnDataChangeNotification_StateAsInteger(object sender, EasyUADataChangeNotificationEventArgs eventArgs)
        {
            // Obtain the integer state we have passed in.
            var stateAsInteger = (int) eventArgs.Arguments.State;

            // Display the data.
            if (eventArgs.Succeeded)
                Console.WriteLine($"{stateAsInteger}: {eventArgs.AttributeData}");
            else
                Console.WriteLine($"{stateAsInteger} *** Failure: {eventArgs.ErrorMessageBrief}");
        }
    }
}
Rem This example shows how to subscribe to changes of multiple monitored items
Rem and display each change, identifying the different subscriptions by an
Rem integer.

' The client object, with events
'Public WithEvents Client6 As EasyUAClient

Public Sub SubscribeMultipleMonitoredItems_StateAsInteger_Command_Click()
    OutputText = ""

    Set Client6 = New EasyUAClient

    OutputText = OutputText & "Subscribing..." & vbCrLf
    Dim MonitoringParameters As New UAMonitoringParameters
    MonitoringParameters.SamplingInterval = 1000
    
    Dim MonitoredItemArguments1 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments1.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments1.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10845"
    Set MonitoredItemArguments1.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments1.SetState 1 ' An integer we have chosen to identify the subscription
    
    Dim MonitoredItemArguments2 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments2.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments2.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10853"
    Set MonitoredItemArguments2.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments2.SetState 2 ' An integer we have chosen to identify the subscription
    
    Dim MonitoredItemArguments3 As New EasyUAMonitoredItemArguments
    MonitoredItemArguments3.endpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
    MonitoredItemArguments3.nodeDescriptor.NodeId.expandedText = "nsu=http://test.org/UA/Data/ ;i=10855"
    Set MonitoredItemArguments3.MonitoringParameters = MonitoringParameters
    MonitoredItemArguments3.SetState 3 ' An integer we have chosen to identify the subscription
    
    Dim arguments(2) As Variant
    Set arguments(0) = MonitoredItemArguments1
    Set arguments(1) = MonitoredItemArguments2
    Set arguments(2) = MonitoredItemArguments3
    Dim handleArray As Variant
    handleArray = Client6.SubscribeMultipleMonitoredItems(arguments)

    Dim i As Long: For i = LBound(handleArray) To UBound(handleArray)
        OutputText = OutputText & "handleArray(" & i & "): " & handleArray(i) & vbCrLf
    Next

    OutputText = OutputText & "Processing monitored item changed events for 10 seconds..." & vbCrLf
    Pause 10000

    OutputText = OutputText & "Unsubscribing..." & vbCrLf
    Call Client6.UnsubscribeAllMonitoredItems

    OutputText = OutputText & "Waiting for 5 seconds..." & vbCrLf
    Pause 5000

    Set Client2 = Nothing
    OutputText = OutputText & "Finished." & vbCrLf
End Sub

Public Sub Client6_DataChangeNotification(ByVal sender As Variant, ByVal eventArgs As EasyUADataChangeNotificationEventArgs)
    ' Obtain the integer state we have passed in.
    Dim stateAsInteger As Integer: stateAsInteger = eventArgs.arguments.State
    If eventArgs.Succeeded Then
        OutputText = OutputText & stateAsInteger & ": " & eventArgs.AttributeData & vbCrLf
    Else
        OutputText = OutputText & stateAsInteger & " *** Failure: " & eventArgs.ErrorMessageBrief & vbCrLf
    End If
End Sub
// This example shows how to subscribe to changes of multiple monitored items
// and display each change, identifying the different subscriptions by an
// object.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeMultipleMonitoredItems
    {
        class CustomObject
        {
            public CustomObject(string name)
            {
                Name = name;
            }

            public string Name { get; }
        }
        

        public static void StateAsObject()
        {
            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 and hook events
            var client = new EasyUAClient();
            client.DataChangeNotification += ClientOnDataChangeNotification_StateAsObject;

            Console.WriteLine("Subscribing...");
            int[] handleArray = client.SubscribeMultipleMonitoredItems(new[]
                {
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10845", 1000)
                        {State = new CustomObject("First")},    // A custom object that corresponds to the subscription
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10853", 1000)
                        {State = new CustomObject("Second")},    // A custom object that corresponds to the subscription
                    new EasyUAMonitoredItemArguments(null, endpointDescriptor, 
                        "nsu=http://test.org/UA/Data/ ;i=10855", 1000)
                        {State = new CustomObject("Third")},    // A custom object that corresponds to the subscription
                });

            for (int i = 0; i < handleArray.Length; i++)
                Console.WriteLine($"handleArray[{i}]: {handleArray[i]}");

            Console.WriteLine("Processing monitored item changed events for 10 seconds...");
            Thread.Sleep(10 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void ClientOnDataChangeNotification_StateAsObject(object sender, EasyUADataChangeNotificationEventArgs eventArgs)
        {
            // Obtain the custom object we have passed in.
            var stateAsObject = (CustomObject) eventArgs.Arguments.State;

            // Display the data
            if (eventArgs.Succeeded)
                Console.WriteLine($"{stateAsObject.Name}: {eventArgs.AttributeData}");
            else
                Console.WriteLine($"{stateAsObject.Name} *** Failure: {eventArgs.ErrorMessageBrief}");
        }
    }
}
// This example shows how to subscribe to changes of all data variables under a specified object in OPC UA address space.

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

namespace UADocExamples._EasyUAClient
{
    partial class SubscribeMultipleMonitoredItems
    {
        public static void AllInObject()
        {
            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 and hook events
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification_AllInObject;

            // Obtain variables under "Scalar" node
            Console.WriteLine("Browsing...");
            UANodeElementCollection nodeElementCollection;
            try
            {
                nodeElementCollection = client.BrowseDataVariables(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;ns=2;i=10787");
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Create array with monitored item arguments
            EasyUAMonitoredItemArguments[] monitoredItemArgumentsArray = nodeElementCollection
                .Select(element => new EasyUAMonitoredItemArguments(null, endpointDescriptor, element))
                .ToArray();

            Console.WriteLine("Subscribing...");
            client.SubscribeMultipleMonitoredItems(monitoredItemArgumentsArray);

            Console.WriteLine("Processing monitored item changed events for 20 seconds...");
            System.Threading.Thread.Sleep(20 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);
        }

        static void client_DataChangeNotification_AllInObject(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value
            if (e.Succeeded)
                Console.WriteLine("{0}: {1}", e.Arguments.NodeDescriptor, e.AttributeData.Value);
            else
                Console.WriteLine("{0} *** Failure: {1}", e.Arguments.NodeDescriptor, e.ErrorMessageBrief);
        }
    }
}
// Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

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

namespace UADocExamples.ComplexData._EasyUAClient
{
    class SubscribeDataChange
    {
        public static void Main1()
        {
            // Define which server and node we will work with.
            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/"
            UANodeDescriptor nodeDescriptor =
                "nsu=http://test.org/UA/Data/ ;i=10867"; // [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

            // Instantiate the client object and hook the event handler.
            var client = new EasyUAClient();
            client.DataChangeNotification += client_DataChangeNotification;

            // Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just 
            // the data returned is different.
            Console.WriteLine("Subscribing...");
            client.SubscribeDataChange(endpointDescriptor, nodeDescriptor, samplingInterval:1000);

            Console.WriteLine("Processing data change events for 20 seconds...");
            System.Threading.Thread.Sleep(20 * 1000);

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

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            // Unhook the event handler.
            client.DataChangeNotification -= client_DataChangeNotification;


            // Example output:
            //
            //Subscribing...
            //Processing data change events for 20 seconds...
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ArrayValueDataType) structured
            //(ArrayValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //(ScalarValueDataType) structured
            //Unsubscribing...
            //Waiting for 5 seconds...
        }

        static void client_DataChangeNotification(object sender, EasyUADataChangeNotificationEventArgs e)
        {
            // Display value
            if (e.Succeeded)
                Console.WriteLine("Value: {0}", e.AttributeData.Value);
            else
                Console.WriteLine("*** Failure: {0}", e.ErrorMessageBrief);

            // For processing the internals of the data, refer to examples for GenericData and DataType classes.
        }
    }
}
// Shows how to subscribe to complex data with OPC UA Complex Data plug-in.

type
  TClientEventHandlers33 = class
    procedure OnDataChangeNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUADataChangeNotificationEventArgs);
  end;

procedure TClientEventHandlers33.OnDataChangeNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUADataChangeNotificationEventArgs);
begin
  // Display value
  if eventArgs.Succeeded then
      WriteLn('Value: ', eventArgs.AttributeData.Value.ToString)
  else
      WriteLn('*** Failure: ', eventArgs.ErrorMessageBrief);

  // For processing the internals of the data, refer to examples for GenericData and DataType classes.
end;

class procedure SubscribeDataChange.Main;
var
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers33;
  EndpointDescriptor: string;
  NodeDescriptor: string;
begin
  // Define which server and node we will work with.
  EndpointDescriptor := 
    //'http://opcua.demo-this.com:51211/UA/SampleServer';
    //'https://opcua.demo-this.com:51212/UA/SampleServer/';
    'opc.tcp://opcua.demo-this.com:51210/UA/SampleServer';
  NodeDescriptor := 'nsu=http://test.org/UA/Data/ ;i=10867';  // [ObjectsFolder]/Data.Dynamic.Scalar.StructureValue

  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers33.Create;
  Client.OnDataChangeNotification := ClientEventHandlers.OnDataChangeNotification;

  // Subscribe to a node which returns complex data. This is done in the same way as regular subscribes - just
  // the data returned is different.
  WriteLn('Subscribing...');
  Client.SubscribeDataChange(EndpointDescriptor, NodeDescriptor, 1000);

  WriteLn('Processing data change events for 20 seconds...');
  PumpSleep(20*1000);

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

  WriteLn('Waiting for 5 seconds...');
  PumpSleep(5*1000);

  WriteLn('Finished.');
  FreeAndNil(Client);
  FreeAndNil(ClientEventHandlers);

  // Example output:
  //
  //Subscribing...
  //Processing data change events for 20 seconds...
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ArrayValueDataType) structured
  //(ArrayValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //(ScalarValueDataType) structured
  //Unsubscribing...
  //Waiting for 5 seconds...
end;
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

Reference

EasyUAClientCore Class
EasyUAClientCore Members

 

 

Copyright © 2004-2023 CODE Consulting and Development, s.r.o., Plzen. All rights reserved. Web page: www.opclabs.com

Send Documentation Feedback. Resources: Knowledge Base. Technical support: Online Forums, FAQ.