ReadMultipleItemValues Method (

Reads named items from an OPC server or OPC servers. Only the item values are returned (qualities and timestamps are not returned). Reads multiple named item values from a single OPC server, using array of argument objects as an input.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ElementsNotNullAttribute()>
<NotNullAttribute()>
Function ReadMultipleItemValues( _
   ByVal argumentsArray As Object _
) As Object()

'Usage
 
Dim instance As _EasyDAClient
Dim argumentsArray As Object
Dim value() As Object
 
value = instance.ReadMultipleItemValues(argumentsArray)

[ElementsNotNull()]
[NotNull()]
object[] ReadMultipleItemValues( 
   object argumentsArray
)

[ElementsNotNull()]
[NotNull()]
array<Object^>^ ReadMultipleItemValues( 
   Object^ 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.BaseLib.OperationModel.ValueResult objects. The indices of elements in the output array are the same as those in the input array, .

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

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 ReadMultipleItemValues method requires that the quality is "good" for each item. 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.

Example

.NET

// This example shows how to read values of 4 items at once, and display them.

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

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

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

            for (int i = 0; i < valueResults.Length; i++)
            {
                ValueResult valueResult = valueResults[i];
                Debug.Assert(!(valueResult is null));

                if (valueResult.Succeeded)
                    Console.WriteLine($"valueResults({i}).Value: {valueResult.Value}");
                else
                    Console.WriteLine($"valueResults({i}) *** Failure: {valueResult.ErrorMessageBrief}");
            }
        }


        // Example output:
        //
        //valueResults(0).Value: 0.00125125888851588
        //valueResults(1).Value: 0.732510924339294
        //valueResults(2).Value: -0.993968485238202
        //valueResults(3).Value: 0
    }
}

# This example shows how to read values of 4 items at once, and display them.

# 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()

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

# This example shows how to read values of 4 items at once, and display them.

#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

$valueResults = [IEasyDAClientExtension]::ReadMultipleItemValues($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 $valueResults.Length; $i++) {
    $valueResult = $valueResults[$i]
    if ($valueResult.Succeeded) {
        Write-Host "valueResults($($i)).Value: $($valueResult.Value)"
    }
    else {
        Write-Host "valueResults($($i)) *** Failure: $($valueResult.ErrorMessageBrief)"
    }
}


# Example output:
#
#valueResults(0).Value: 0.00125125888851588
#valueResults(1).Value: 0.732510924339294
#valueResults(2).Value: -0.993968485238202
#valueResults(3).Value: 0

Object Pascal
Visual Basic (VB 6.0)
VBScript

// This example shows how to read values of 4 items at once, and display them.

class procedure ReadMultipleItemValues.Main;
var
  Arguments: OleVariant;
  Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
  I: Cardinal;
  ReadItemArguments1: _DAReadItemArguments;
  ReadItemArguments2: _DAReadItemArguments;
  ReadItemArguments3: _DAReadItemArguments;
  ReadItemArguments4: _DAReadItemArguments;
  ValueResult: _ValueResult;
  Results: OleVariant;
begin
  ReadItemArguments1 := CoDAReadItemArguments.Create;
  ReadItemArguments1.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ReadItemArguments1.ItemDescriptor.ItemID := 'Simulation.Random';

  ReadItemArguments2 := CoDAReadItemArguments.Create;
  ReadItemArguments2.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ReadItemArguments2.ItemDescriptor.ItemID := 'Trends.Ramp (1 min)';

  ReadItemArguments3 := CoDAReadItemArguments.Create;
  ReadItemArguments3.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ReadItemArguments3.ItemDescriptor.ItemID := 'Trends.Sine (1 min)';

  ReadItemArguments4 := CoDAReadItemArguments.Create;
  ReadItemArguments4.ServerDescriptor.ServerClass := 'OPCLabs.KitServer.2';
  ReadItemArguments4.ItemDescriptor.ItemID := 'Simulation.Register_I4';

  Arguments := VarArrayCreate([0, 3], varVariant);
  Arguments[0] := ReadItemArguments1;
  Arguments[1] := ReadItemArguments2;
  Arguments[2] := ReadItemArguments3;
  Arguments[3] := ReadItemArguments4;

  // Instantiate the client object
  Client := CoEasyDAClient.Create;

  TVarData(Results).VType := varArray or varVariant;
  TVarData(Results).VArray := PVarArray(
    Client.ReadMultipleItemValues(Arguments));

  // Display results
  for I := VarArrayLowBound(Results, 1) to VarArrayHighBound(Results, 1) do
  begin
      ValueResult := IInterface(Results[I]) as _ValueResult;

      if ValueResult.Succeeded then
        WriteLn('results(', i, ').Value: ', ValueResult.Value)
      else
        WriteLn('results(', i, ') *** Failure: ', ValueResult.ErrorMessageBrief);
  end;

  VarClear(Results);
  VarClear(Arguments);
end;

Rem This example shows how to read values of 4 items at once, and display them.

Private Sub ReadMultipleItemValues_Main_Command_Click()
    OutputText = ""
    
    Dim readArguments1 As New DAReadItemArguments
    readArguments1.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    readArguments1.ItemDescriptor.itemId = "Simulation.Random"
    
    Dim readArguments2 As New DAReadItemArguments
    readArguments2.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    readArguments2.ItemDescriptor.itemId = "Trends.Ramp (1 min)"
    
    Dim readArguments3 As New DAReadItemArguments
    readArguments3.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    readArguments3.ItemDescriptor.itemId = "Trends.Sine (1 min)"
    
    Dim readArguments4 As New DAReadItemArguments
    readArguments4.serverDescriptor.ServerClass = "OPCLabs.KitServer.2"
    readArguments4.ItemDescriptor.itemId = "Simulation.Register_I4"
    
    Dim arguments(3) As Variant
    Set arguments(0) = readArguments1
    Set arguments(1) = readArguments2
    Set arguments(2) = readArguments3
    Set arguments(3) = readArguments4

    ' Instantiate the client object
    Dim client As New EasyDAClient

    Dim results() As Variant
    results = client.ReadMultipleItemValues(arguments)

    ' Display results
    Dim i: For i = LBound(results) To UBound(results)
        Dim valueResult As valueResult: Set valueResult = results(i)
        If valueResult.Succeeded Then
            OutputText = OutputText & "results(" & i & ").Value: " & valueResult.value & vbCrLf
        Else
            OutputText = OutputText & "results(" & i & ") *** Failure: " & valueResult.ErrorMessageBrief & vbCrLf
        End If
    Next
End Sub

Rem This example shows how to read values of 4 items at once, and display them.

Option Explicit

Dim ReadItemArguments1: Set ReadItemArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments1.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments1.ItemDescriptor.ItemID = "Simulation.Random"

Dim ReadItemArguments2: Set ReadItemArguments2 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments2.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments2.ItemDescriptor.ItemID = "Trends.Ramp (1 min)"

Dim ReadItemArguments3: Set ReadItemArguments3 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments3.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments3.ItemDescriptor.ItemID = "Trends.Sine (1 min)"

Dim ReadItemArguments4: Set ReadItemArguments4 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments4.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments4.ItemDescriptor.ItemID = "Simulation.Register_I4"

Dim arguments(3)
Set arguments(0) = ReadItemArguments1
Set arguments(1) = ReadItemArguments2
Set arguments(2) = ReadItemArguments3
Set arguments(3) = ReadItemArguments4

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
Dim results: results = Client.ReadMultipleItemValues(arguments)

Dim i: For i = LBound(results) To UBound(results)
    Dim ValueResult: Set ValueResult = results(i)
    If ValueResult.Succeeded Then
        WScript.Echo "results(" & i & ").Value: " & ValueResult.Value
    Else
        WScript.Echo "results(" & i & ") *** Failure: " & ValueResult.ErrorMessageBrief
    End If
Next

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

_EasyDAClient Interface
_EasyDAClient Members

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