ItemDescriptor Property (DAItemArguments)

Gets or sets the OPC item descriptor that is an argument to the operation.

Syntax

[DataMember()]
public DAItemDescriptor ItemDescriptor {get; set;}

[DataMember()]
public:
property DAItemDescriptor^ ItemDescriptor {
   DAItemDescriptor^ get();
   void set (    DAItemDescriptor^ value);
}

'Declaration
 
<DataMemberAttribute()>
Public Property ItemDescriptor As DAItemDescriptor

'Usage
 
Dim instance As DAItemArguments
Dim value As DAItemDescriptor
 
instance.ItemDescriptor = value
 
value = instance.ItemDescriptor

Property Value

The value of this property cannot be null (Nothing in Visual Basic).

Exceptions

Exception Description

Exception	Description
System.ArgumentNullException	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.

System.ArgumentNullException

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

Because the OpcLabs.EasyOpc.DataAccess.DAItemDescriptor has an implicit conversion from System.String and OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the qualified name of the node), or a OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement object (result from OPC browsing), in place of OpcLabs.EasyOpc.DataAccess.DAItemDescriptor value when setting this property, and the corresponding OPC DA item descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the FromString or FromDANodeElement static method instead.

Example

// Shows how to write into multiple OPC items using a single method call, specifying their requested data types.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

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

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

            Console.WriteLine("Writing multiple item values...");
            OperationResult[] resultArray = client.WriteMultipleItemValues(new[] { 
                    new DAItemValueArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I2", 12345) 
                        { ItemDescriptor = { RequestedDataType = VarTypes.I2}}, // <-- the requested data type
                    new DAItemValueArguments("", "OPCLabs.KitServer.2", "Simulation.Register_R4", 234.56)
                        { ItemDescriptor = { RequestedDataType = VarTypes.R4}}  // <-- the requested data type 
                });


            for (int i = 0; i < resultArray.Length; i++)
            {
                Debug.Assert(resultArray[i] != null);
                if (resultArray[i].Succeeded)
                    Console.WriteLine("Result {0}: success", i);
                else
                {
                    Debug.Assert(!(resultArray[i].Exception is null));
                    Console.WriteLine("Result {0} *** Failure: {1}", i, resultArray[i].ErrorMessageBrief);
                }
            }

            Console.WriteLine("Reading multiple item values...");
            ValueResult[] valueResultArray = client.ReadMultipleItemValues("OPCLabs.KitServer.2",
                new DAItemDescriptor[] { "Simulation.Register_I2", "Simulation.Register_R4" });

            for (int i = 0; i < valueResultArray.Length; i++)
            {
                Debug.Assert(valueResultArray[i] != null);
                Console.WriteLine("valueResultArray[{0}]: {1}", i, valueResultArray[i]);
            }
        }
    }
}

' Shows how to write into multiple OPC items using a single method call, specifying their requested data types.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.

Imports OpcLabs.BaseLib.ComInterop
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.DataAccess.OperationModel

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

            Console.WriteLine("Writing multiple item values...")
            Dim resultArray = client.WriteMultipleItemValues(New DAItemValueArguments() { _
                New DAItemValueArguments("", "OPCLabs.KitServer.2", "Simulation.Register_I2", 12345) With _
                {.ItemDescriptor = New DAItemDescriptor() With {.RequestedDataType = VarTypes.I2}}, _
                New DAItemValueArguments("", "OPCLabs.KitServer.2", "Simulation.Register_R4", 234.56) With _
                {.ItemDescriptor = New DAItemDescriptor() With {.RequestedDataType = VarTypes.R4}} _
            })

            For i = 0 To resultArray.Length - 1
                Debug.Assert(resultArray(i) IsNot Nothing)
                If resultArray(i).Succeeded Then
                    Console.WriteLine("Result {0}: success", i)
                Else
                    Debug.Assert(resultArray(i).Exception IsNot Nothing)
                    Console.WriteLine("Result {0} *** Failure: {1}", i, resultArray(i).ErrorMessageBrief)
                End If
            Next i

            Console.WriteLine("Reading multiple item values...")
            Dim valueResultArray = client.ReadMultipleItemValues("OPCLabs.KitServer.2",
                    New DAItemDescriptor() {"Simulation.Register_I2", "Simulation.Register_R4"})

            For i = 0 To valueResultArray.Length - 1
                Debug.Assert(valueResultArray(i) IsNot Nothing)
                Console.WriteLine("valueResultArray[{0}]: {1}", i, valueResultArray(i))
            Next i
        End Sub
    End Class
End Namespace

# Shows how to write into multiple OPC items using a single method call, specifying their requested data types.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.BaseLib.ComInterop import *
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()

print('Writing multiple item values...')
arguments1 = DAItemValueArguments(ServerDescriptor('OPCLabs.KitServer.2'),
                                  DAItemDescriptor('Simulation.Register_I2'),
                                  12345)
arguments1.ItemDescriptor.RequestedDataType = VarType(VarTypes.I2)  # <-- the requested data type
arguments2 = DAItemValueArguments(ServerDescriptor('OPCLabs.KitServer.2'),
                                  DAItemDescriptor('Simulation.Register_R4'),
                                  234.56)
arguments2.ItemDescriptor.RequestedDataType = VarType(VarTypes.R4)  # <-- the requested data type
operationResultArray = client.WriteMultipleItemValues([arguments1, arguments2])

for i, operationResult in enumerate(operationResultArray):
    assert operationResult is not None
    if operationResult.Succeeded:
        print('operationResultArray[', i, ']: success', sep='')
    else:
        assert operationResult.Exception is not None
        print('operationResultArray[', i, '] *** Failure: ', operationResult.ErrorMessageBrief, sep='')

print('Reading multiple item values...')
try:
    valueResultArray = IEasyDAClientExtension.ReadMultipleItemValues(client, ServerDescriptor('OPCLabs.KitServer.2'), [
        DAItemDescriptor('Simulation.Register_I2'),
        DAItemDescriptor('Simulation.Register_R4'),
    ])
except OpcException as opcException:
    print('*** Failure: ' + opcException.GetBaseException().Message, sep='')
    exit()

for i, valueResult in enumerate(valueResultArray):
    assert valueResult is not None
    if valueResult.Succeeded:
        print('valueResultArray[', i, '].Value: ', valueResult.Value, sep='')
    else:
        assert valueResult.Exception is not None
        print('valueResultArray[', i, '] *** Failure: ', valueResult.ErrorMessageBrief, sep='')

print('Finished.')

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

Reference

DAItemArguments Class
DAItemArguments Members

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