OPC Studio User's Guide and Reference
ReadMultipleItems Method (IEasyDAClient)
Example 



OpcLabs.EasyOpcClassicCore Assembly > OpcLabs.EasyOpc.DataAccess Namespace > IEasyDAClient Interface : ReadMultipleItems Method
Array of arguments, one element per each OPC item involved in the operation.
Reads multiple named items from an OPC server or OPC servers, using array of argument objects as an input. Values, qualities and timestamps are returned.
Syntax
'Declaration
 
<ElementsNotNullAttribute()>
<NotNullAttribute()>
Function ReadMultipleItems( _
   ByVal argumentsArray() As DAReadItemArguments _
) As DAVtqResult()
'Usage
 
Dim instance As IEasyDAClient
Dim argumentsArray() As DAReadItemArguments
Dim value() As DAVtqResult
 
value = instance.ReadMultipleItems(argumentsArray)
[ElementsNotNull()]
[NotNull()]
DAVtqResult[] ReadMultipleItems( 
   DAReadItemArguments[] argumentsArray
)
[ElementsNotNull()]
[NotNull()]
array<DAVtqResult^>^ ReadMultipleItems( 
   array<DAReadItemArguments^>^ argumentsArray
) 

Parameters

argumentsArray
Array of arguments, one element per each OPC item involved in the operation.

Return Value

The function returns an array of OpcLabs.EasyOpc.DataAccess.OperationModel.DAVtqResult objects. The indices of elements in the output array are the same as those in the input array, argumentsArray.
Exceptions
ExceptionDescription

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

Remarks

The servers can be local or can be remotely accessed via DCOM. Optionally, an access path can be specified or a specific data type can be requested.

The ReadMultipleItems method only waits for the first update from the server (or until the timeout elapses) for each item; it does not wait until the quality becomes "uncertain" or "good". The function performs all individual operations in parallel, but only returns after all individual operations are completed (or their timeouts elapse).

This method does not throw an exception in case of OPC operation failures. Instead, the eventual exception related to each item is returned in Exception property of each returned OpcLabs.EasyOpc.DataAccess.OperationModel.DAVtqResult element.

The size of the input array will become the size of the output array. The element positions (indices) in the output array are the same as in the input array.

 

This is a multiple-operation method. In a properly written program, it does not throw any exceptions. You should therefore not put try/catch statements or similar constructs around calls to this method. The only exceptions thrown by this method are for usage errors, i.e. when your code violates the usage contract of the method, such as passing in invalid arguments or calling the method when the state of the object does not allow it. Any operation-related errors (i.e. errors that depend on external conditions that your code cannot reliably check) are indicated in the result objects returned by the method. For more information, see Multiple-operation Methods and Do not catch any exceptions with asynchronous or multiple-operation methods.
Example

.NET

COM

.NET

.NET

.NET

// This example shows how to read 4 items at once, and display their values, timestamps and qualities.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

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

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        public static void Main1()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            DAVtqResult[] vtqResults = client.ReadMultipleItems("OPCLabs.KitServer.2",
                new DAItemDescriptor[]
                    {
                        "Simulation.Random", "Trends.Ramp (1 min)", "Trends.Sine (1 min)", "Simulation.Register_I4"
                    });

            for (int i = 0; i < vtqResults.Length; i++)
            {
                Debug.Assert(vtqResults[i] != null);

                if (vtqResults[i].Succeeded)
                    Console.WriteLine("vtqResults[{0}].Vtq: {1}", i, vtqResults[i].Vtq);
                else
                    Console.WriteLine("vtqResults[{0}] *** Failure: {1}", i, vtqResults[i].ErrorMessageBrief);
            }
        }
    }
}
# This example shows how to read 4 items at once, and display their values, timestamps and qualities.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.DataAccess

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"

# Instantiate the client object.
$client = New-Object EasyDAClient

$vtqResults = [IEasyDAClientExtension]::ReadMultipleItems($client, "OPCLabs.KitServer.2", @(
    (New-Object DAItemDescriptor("Simulation.Random")),
    (New-Object DAItemDescriptor("Trends.Ramp (1 min)")),
    (New-Object DAItemDescriptor("Trends.Sine (1 min)")),
    (New-Object DAItemDescriptor("Simulation.Register_I4"))
    ))

for ($i = 0; $i -lt $vtqResults.Length; $i++) {
    $vtqResult = $vtqResults[$i]
    if ($vtqResult.Succeeded) {
        Write-Host "vtqResults[$($i)].Vtq: $($vtqResult.Vtq)"
    }
    else {
        Write-Host "vtqResults[$($i)] *** Failure: $($vtqResult.ErrorMessageBrief)"
    }
}
# This example shows how to read 4 items at once, and display their values, timestamps and qualities.
#
# 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 .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

#
vtqResultArray = client.ReadMultipleItems([
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Random')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Ramp (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Sine (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Register_I4')),
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')
' This example shows how to read 4 items at once, and display their values, timestamps and qualities.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class ReadMultipleItems
        Public Shared Sub Main1()
            Dim client = New EasyDAClient()

            Dim vtqResults() As DAVtqResult = client.ReadMultipleItems(
                "OPCLabs.KitServer.2",
                New DAItemDescriptor() {"Simulation.Random", "Trends.Ramp (1 min)", "Trends.Sine (1 min)", "Simulation.Register_I4"})

            For i = 0 To vtqResults.Length - 1
                Debug.Assert(vtqResults(i) IsNot Nothing)

                If vtqResults(i).Succeeded Then
                    Console.WriteLine("vtqResult[{0}].Vtq: {1}", i, vtqResults(i).Vtq)
                Else
                    Console.WriteLine("vtqResult[{0}] *** Failure: {1}", i, vtqResults(i).ErrorMessageBrief)
                End If
            Next i
        End Sub
    End Class
End Namespace
// This example shows how to read 4 items at once, and display their values, timestamps and qualities.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

$ReadItemArguments1 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments1->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments1->ItemDescriptor->ItemID = "Simulation.Random";

$ReadItemArguments2 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments2->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments2->ItemDescriptor->ItemID = "Trends.Ramp (1 min)";

$ReadItemArguments3 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments3->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments3->ItemDescriptor->ItemID = "Trends.Sine (1 min)";

$ReadItemArguments4 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments4->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments4->ItemDescriptor->ItemID = "Simulation.Register_I4";

$arguments[0] = $ReadItemArguments1;
$arguments[1] = $ReadItemArguments2;
$arguments[2] = $ReadItemArguments3;
$arguments[3] = $ReadItemArguments4;

$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");

$results = $Client->ReadMultipleItems($arguments);

for ($i = 0; $i < count($results); $i++)
{
    $VtqResult = $results[$i];
    if ($VtqResult->Succeeded)
        printf("results[d].Vtq.ToString()s\n", $i, $VtqResult->Vtq->ToString);
    else
        printf("results[d]: *** Failures\n", $i, $VtqResult->ErrorMessageBrief);
}
// This example shows how to read 4 items from an OPC XML-DA server at once, and display their values, timestamps 
// and qualities.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

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

namespace DocExamples.DataAccess.Xml
{
    partial class ReadMultipleItems
    {
        public static void Main1Xml()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            DAVtqResult[] vtqResults = client.ReadMultipleItems(
                new ServerDescriptor { UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx" },
                new DAItemDescriptor[]
                    {
                        "Dynamic/Analog Types/Double", 
                        "Dynamic/Analog Types/Double[]", 
                        "Dynamic/Analog Types/Int", 
                        "SomeUnknownItem"
                    });

            for (int i = 0; i < vtqResults.Length; i++)
            {
                Debug.Assert(vtqResults[i] != null);

                if (!(vtqResults[i].Exception is null))
                {
                    Console.WriteLine($"vtqResults[{i}] *** Failure: {vtqResults[i].ErrorMessageBrief}");
                    continue;
                }
                Console.WriteLine($"vtqResults[{i}].Vtq: {vtqResults[i].Vtq}");
            }
        }
    }
}
# This example shows how to read 4 items from an OPC XML-DA server at once, and display their values, timestamps 
# and qualities.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc
using namespace OpcLabs.EasyOpc.DataAccess

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicCore.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassic.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcClassicComponents.dll"

# Instantiate the client object.
$client = New-Object EasyDAClient

$serverDescriptor = New-Object ServerDescriptor -Property @{
    UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx"
}

$vtqResults = [IEasyDAClientExtension]::ReadMultipleItems($client, 
    $serverDescriptor, 
    @(
        (New-Object DAItemDescriptor("Dynamic/Analog Types/Double")),
        (New-Object DAItemDescriptor("Dynamic/Analog Types/Double[]")),
        (New-Object DAItemDescriptor("Dynamic/Analog Types/Int")),
        (New-Object DAItemDescriptor("SomeUnknownItem"))
        ))

for ($i = 0; $i -lt $vtqResults.Length; $i++) {
    $vtqResult = $vtqResults[$i]
    if ($vtqResult.Succeeded) {
        Write-Host "vtqResults[$($i)].Vtq: $($vtqResult.Vtq)"
    }
    else {
        Write-Host "vtqResults[$($i)] *** Failure: $($vtqResult.ErrorMessageBrief)"
    }
}
# This example shows how to read 4 items from an OPC XML-DA server at once, and display their values, timestamps
# and qualities.
#
# 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 .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

#
vtqResultArray = IEasyDAClientExtension.ReadMultipleItems(client,
    ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'),
    [
        DAItemDescriptor('Dynamic/Analog Types/Double'),
        DAItemDescriptor('Dynamic/Analog Types/Double[]'),
        DAItemDescriptor('Dynamic/Analog Types/Int'),
        DAItemDescriptor('SomeUnknownItem')
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')
' This example shows how to read 4 items from an OPC XML-DA server at once, and display their values, timestamps 
' and qualities.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess.Xml
    Partial Friend Class ReadMultipleItems
        Public Shared Sub Main1Xml()
            Dim client = New EasyDAClient()

            Dim vtqResults() As DAVtqResult = client.ReadMultipleItems(
                    New ServerDescriptor() With {.UrlString = "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx"},
                    New DAItemDescriptor() _
                    { _
                        "Dynamic/Analog Types/Double",
                        "Dynamic/Analog Types/Double[]",
                        "Dynamic/Analog Types/Int",
                        "SomeUnknownItem"
                    })

            For i = 0 To vtqResults.Length - 1
                Debug.Assert(vtqResults(i) IsNot Nothing)

                If vtqResults(i).Exception IsNot Nothing Then
                    Console.WriteLine("vtqResult[{0}] *** Failure: {1}", i, vtqResults(i).ErrorMessageBrief)
                    Continue For
                End If
                Console.WriteLine("vtqResult[{0}].Vtq: {1}", i, vtqResults(i).Vtq)
            Next i
        End Sub
    End Class
End Namespace
// This example repeatedly reads a large number of items.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

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

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        private const int RepeatCount = 10;
        private const int NumberOfItems = 1000;

        public static void ManyRepeat()
        {
            Console.WriteLine("Creating array of arguments...");
            var arguments = new DAReadItemArguments[NumberOfItems];
            for (int i = 0; i < NumberOfItems; i++)
            {
                int copy = (i / 100) + 1;
                int phase = i % 100;
                string itemId = FormattableString.Invariant($"Simulation.Incrementing.Copy_{copy}.Phase_{phase}");
                Console.WriteLine(itemId);

                var readItemArguments = new DAReadItemArguments("OPCLabs.KitServer.2", itemId);
                arguments[i] = readItemArguments;
            }

            // Instantiate the client object.
            var client = new EasyDAClient();

            for (int iRepeat = 1; iRepeat <= RepeatCount; iRepeat++)
            {
                Console.WriteLine("Reading items...");
                DAVtqResult[] vtqResults = client.ReadMultipleItems(arguments);

                int successCount = 0;
                foreach (DAVtqResult vtqResult in vtqResults)
                    if (vtqResult.Succeeded)
                        successCount++;
                Console.WriteLine($"Success count: {successCount}");
            }
        }
    }
}
' This example repeatedly reads a large number of items.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class ReadMultipleItems

        Private Const RepeatCount As Integer = 10
        Private Const NumberOfItems As Integer = 1000

        Public Shared Sub ManyRepeat()
            Console.WriteLine("Creating array of arguments...")
            Dim arguments = New DAReadItemArguments(NumberOfItems - 1) {}
            For i As Integer = 0 To NumberOfItems - 1
                Dim copy As Integer = (i \ 100) + 1
                Dim phase As Integer = (i Mod 100)
                Dim itemId As String = String.Format($"Simulation.Incrementing.Copy_{copy}.Phase_{phase}")
                Console.WriteLine(itemId)

                Dim readItemArguments As DAReadItemArguments = New DAReadItemArguments("OPCLabs.KitServer.2", itemId)
                arguments(i) = readItemArguments
            Next i

            ' Instantiate the client object.
            Dim client = New EasyDAClient()

            For iRepeat = 1 To RepeatCount
                Console.WriteLine("Reading items...")
                Dim vtqResults() As DAVtqResult = client.ReadMultipleItems(arguments)

                Dim successCount As Integer = 0
                For Each vtqResult In vtqResults
                    If vtqResult.Succeeded Then
                        successCount += 1
                    End If
                Next vtqResult

                Console.WriteLine($"Success count: {successCount}")
            Next iRepeat
        End Sub
    End Class
End Namespace
// This example shows how to read items while subscribed.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

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

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

                Console.WriteLine("Subscribing item changes...");
                client.SubscribeMultipleItems(
                    new[] {
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, null), 
                            new DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, null),  
                        });

                Console.WriteLine("Waiting for 10 seconds...");
                Thread.Sleep(10 * 1000);

                Console.WriteLine("Reading items...");
                DAVtqResult[] vtqResults = client.ReadMultipleItems("OPCLabs.KitServer.2",
                    new DAItemDescriptor[]
                    {
                        "Trends.Ramp (1 min)", "Trends.Sine (1 min)"
                    });

                for (int i = 0; i < vtqResults.Length; i++)
                {
                    Debug.Assert(vtqResults[i] != null);

                    if (vtqResults[i].Succeeded)
                        Console.WriteLine("vtqResults[{0}].Vtq: {1}", i, vtqResults[i].Vtq);
                    else
                        Console.WriteLine("vtqResults[{0}] *** Failure: {1}", i, vtqResults[i].ErrorMessageBrief);
                }

                Console.WriteLine("Waiting for 10 seconds...");
                Thread.Sleep(10 * 1000);

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

            Console.WriteLine("Finished.");
        }

        // Item changed event handler
        static void client_Read_ItemChanged(object sender, EasyDAItemChangedEventArgs e)
        {
            if (e.Succeeded)
                Console.WriteLine($"< {e.Arguments.ItemDescriptor.ItemId}: {e.Vtq}");
            else
                Console.WriteLine($"< {e.Arguments.ItemDescriptor.ItemId} *** Failure: {e.ErrorMessageBrief}");
        }
    }
}
# This example shows how to read items while subscribed.
#
# 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 .
# 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 *


# Item changed event handler.
def itemChanged(sender, e):
    if e.Succeeded:
        print('< ', e.Arguments.ItemDescriptor.ItemId, ': ', e.Vtq, sep='')
    else:
        print('< ', e.Arguments.ItemDescriptor.ItemId, ' *** Failure: ', e.ErrorMessageBrief, sep='')


# Instantiate the client object.
client = EasyDAClient()

client.ItemChanged += itemChanged

print('Subscribing item changes...')
client.SubscribeMultipleItems([
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Simulation.Random', 1000, None),
    EasyDAItemSubscriptionArguments('', 'OPCLabs.KitServer.2', 'Trends.Sine (1 min)', 1000, None),
    ])

print('Processing item change notifications for 10 seconds...')
time.sleep(10)

print('Reading items...')
vtqResultArray = client.ReadMultipleItems([
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Ramp (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Sine (1 min)')),
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')

print('Processing item change notifications for 10 seconds...')
time.sleep(10)

print('Unsubscribing all items...')
client.UnsubscribeAllItems()

client.ItemChanged -= itemChanged

print('Finished.')
' This example shows how to read items while subscribed.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports System.Threading
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class SubscribeMultipleItems
        Public Shared Sub WithRead()
            ' Instantiate the client object.
            Using client = New EasyDAClient()
                AddHandler client.ItemChanged, AddressOf client_Read_ItemChanged

                Console.WriteLine("Subscribing item changes...")
                Dim handleArray() As Integer = client.SubscribeMultipleItems(New DAItemGroupArguments() {
                    New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Simulation.Random", 1000, Nothing),
                    New DAItemGroupArguments("", "OPCLabs.KitServer.2", "Trends.Sine (1 min)", 1000, Nothing)
                })

                Console.WriteLine("Waiting for 10 seconds...")
                Thread.Sleep(10 * 1000)

                Console.WriteLine("Reading items...")
                Dim vtqResults() As DAVtqResult = client.ReadMultipleItems("OPCLabs.KitServer.2",
                    New DAItemDescriptor() {"Trends.Ramp (1 min)", "Trends.Sine (1 min)"})

                For i = 0 To vtqResults.Length - 1
                    Debug.Assert(vtqResults(i) IsNot Nothing)

                    If vtqResults(i).Succeeded Then
                        Console.WriteLine("vtqResult[{0}].Vtq: {1}", i, vtqResults(i).Vtq)
                    Else
                        Console.WriteLine("vtqResult[{0}] *** Failure: {1}", i, vtqResults(i).ErrorMessageBrief)
                    End If
                Next i

                Console.WriteLine("Waiting for 10 seconds...")
                Thread.Sleep(10 * 1000)

                Console.WriteLine("Unsubscribing item changes...")
            End Using

            Console.WriteLine("Finished.")
        End Sub

        ' Item changed event handler
        Private Shared Sub client_Read_ItemChanged(ByVal sender As Object, ByVal e As EasyDAItemChangedEventArgs)
            If e.Succeeded Then
                Console.WriteLine($"< {e.Arguments.ItemDescriptor.ItemId}: {e.Vtq}")
            Else
                Console.WriteLine($"< {e.Arguments.ItemDescriptor.ItemId} *** Failure: {e.ErrorMessageBrief}")
            End If
        End Sub
    End Class
End Namespace
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