QuickOPC User's Guide and Reference
ItemChanged Event (IEasyDAClient)
Example 



OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.DataAccess Namespace > IEasyDAClient Interface : ItemChanged Event
Raised for every significant change in an OPC item subscribed to by the SubscribeItem method.
Syntax
'Declaration
 
Event ItemChanged As EasyDAItemChangedEventHandler
'Usage
 
Dim instance As IEasyDAClient
Dim handler As EasyDAItemChangedEventHandler
 
AddHandler instance.ItemChanged, handler
event EasyDAItemChangedEventHandler ItemChanged
event EasyDAItemChangedEventHandler^ ItemChanged
Event Data

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

PropertyDescription
Holds arguments that were used to subscribe to an item in an OPC-DA server.  
Diagnostics information (such as warnings) assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Count of diagnostic information elements assembled during the operation. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Textual summary of diagnostics information, one message per line. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets or sets the error ID of the error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets or sets a message that describes the current exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
The first line of the error message. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets the current exception. Contains null reference when no exception. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
A normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Diagnostics collection. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
A normalized OpcLabs.BaseLib.OperationModel.OperationEventArgs.Exception object, or null if there was no error. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Status information corresponding to the contents of the event arguments.  
Gets indication whether the operation has succeeded. (Inherited from OpcLabs.BaseLib.OperationModel.OperationEventArgs)
Gets the current (new) OpcLabs.EasyOpc.DataAccess.DAVtq (value, timestamp and quality) of the OPC item. Null reference when System.Exception is not null.  
Example
// This example shows how subscribe to changes of multiple items and display each change, identifying the different
// subscriptions by an integer.

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

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class SubscribeMultipleItems
    {
        public static void StateAsInteger()
        {
            // Instantiate the client object.
            using (var client = new EasyDAClient())
            {
                // Hook events
                client.ItemChanged += client_StateAsInteger_ItemChanged;

                Console.WriteLine("Subscribing...");
                int[] handleArray = client.SubscribeMultipleItems(new[]
                {
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000,
                        state: 1), // An integer we have chosen to identify the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000,
                        state: 2), // An integer we have chosen to identify the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000,
                        state: 3), // An integer we have chosen to identify the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 1000,
                        state: 4) // 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 item changed events for 10 seconds...");
                Thread.Sleep(10 * 1000);

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

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

            Console.WriteLine("Finished.");
        }

        // Item changed event handler
        static void client_StateAsInteger_ItemChanged(object sender, EasyDAItemChangedEventArgs eventArgs)
        {
            // Obtain the integer state we have passed in.
            var stateAsInteger = (int)eventArgs.Arguments.State;

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

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

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class SubscribeMultipleItems
    {
        class CustomObject
        {
            public CustomObject(string name)
            {
                Name = name;
            }

            public string Name { get; }
        }


        public static void StateAsObject()
        {
            // Instantiate the client object.
            using (var client = new EasyDAClient())
            {
                // Hook events
                client.ItemChanged += client_StateAsObject_ItemChanged;

                Console.WriteLine("Subscribing...");
                int[] handleArray = client.SubscribeMultipleItems(new[]
                {
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000,
                        new CustomObject("First")), // A custom object that corresponds to the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Ramp (1 min)", 1000,
                        new CustomObject("Second")), // A custom object that corresponds to the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000,
                        new CustomObject("Third")), // A custom object that corresponds to the subscription
                    new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 1000,
                        new CustomObject("Fourth")) // 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 item changed events for 10 seconds...");
                Thread.Sleep(10 * 1000);

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

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

            Console.WriteLine("Finished.");
        }

        // Item changed event handler
        static void client_StateAsObject_ItemChanged(object sender, EasyDAItemChangedEventArgs eventArgs)
        {
            // Obtain the custom object we have passed in.
            var stateAsObject = (CustomObject)eventArgs.Arguments.State;

            // Display the data
            if (eventArgs.Succeeded)
                Console.WriteLine($"{stateAsObject.Name}: {eventArgs.Vtq}");
            else
                Console.WriteLine($"{stateAsObject.Name} *** Failure: {eventArgs.ErrorMessageBrief}");
        }
    }
}
Requirements

Target Platforms: .NET Framework: Windows 10, Windows Server 2012, Windows Server 2016; .NET Core, .NET 5: Linux, macOS, Microsoft Windows

See Also