Create<TValue>(String,String,String,Int32) Method

Creates a new item change observable for OPC item, specifying machine name, server class, item ID, requested update rate, and percent deadband.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<NotNullAttribute()>
Public Overloads Shared Function Create(Of TValue)( _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String, _
   ByVal requestedUpdateRate As Integer _
) As DAItemChangedObservable(Of TValue)

'Usage
 
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim requestedUpdateRate As Integer
Dim value As DAItemChangedObservable(Of TValue)
 
value = DAItemChangedObservable.Create(Of TValue)(machineName, serverClass, itemId, requestedUpdateRate)

[NotNull()]
public static DAItemChangedObservable<TValue> Create<TValue>( 
   string machineName,
   string serverClass,
   string itemId,
   int requestedUpdateRate
)

[NotNull()]
public:
static DAItemChangedObservable<TValue^>^ Creategeneric<typename TValue>
( 
   String^ machineName,
   String^ serverClass,
   String^ itemId,
   int requestedUpdateRate
)

Parameters

machineName

Name of the machine (empty string for local computer).

The value represents a UNC or DNS computer name. Any string can be passed to this parameter (i.e. will not cause System.ArgumentException), but not all values make sense and will work when an operation using them is attempted. IPv6 addresses are normally enclosed between '[' and ']'.

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

serverClass

Contains ProgID of the OPC server.

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

itemId

ID of the item that will be subscribed to.

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

requestedUpdateRate

How often should the updates be received (number of milliseconds)

Valid values of this parameter are in the range from -1 to 2147483647 (Int32.MaxValue).

Type Parameters

TValue

Return Value

Returns an observable for changes in the given OPC item.

This method never returns null (Nothing in Visual Basic).

Remarks

The DAReactive.DefaultClientSelector selector will be used for OPC Data Access operations.

Example

CSharp

// Shows how to create an observable for OPC-DA item changes, and subscribe to it.
//
// 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.Threading;
using OpcLabs.EasyOpc.DataAccess.Reactive;

namespace ReactiveDocExamples
{
    namespace _DAItemChangedObservable
    {
        partial class Subscribe
        {
            public static void Main1()
            {
                Console.WriteLine("Creating observable...");
                DAItemChangedObservable<double> ramp = 
                    DAItemChangedObservable.Create<double>("", "OPCLabs.KitServer.2", "Demo.Ramp", 1000);

                Console.WriteLine("Subscribing...");
                using (ramp.Subscribe(e => Console.WriteLine(
                    (e.Exception is null) ? e.Vtq.ToString() : e.Exception.GetBaseException().ToString())))
                {
                    Console.WriteLine("Waiting for 10 seconds...");
                    Thread.Sleep(10*1000);

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

                Console.WriteLine("Waiting for 2 seconds...");
                Thread.Sleep(2 * 1000);
            }
        }
    }
}

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

DAItemChangedObservable Class
DAItemChangedObservable Members
Overload List

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