WaitForValue(IEasyUAClient,UAAttributeArguments) Method

Waits until the specified attribute becomes "good". Specify attribute arguments object, use default wait monitoring parameters.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<CanBeNullAttribute()>
Public Overloads Shared Function WaitForValue( _
   ByVal client As IEasyUAClient, _
   ByVal attributeArguments As UAAttributeArguments _
) As Object

'Usage
 
Dim client As IEasyUAClient
Dim attributeArguments As UAAttributeArguments
Dim value As Object
 
value = IEasyUAClientExtension2.WaitForValue(client, attributeArguments)

[Extension()]
[CanBeNull()]
public static object WaitForValue( 
   IEasyUAClient client,
   UAAttributeArguments attributeArguments
)

[Extension()]
[CanBeNull()]
public:
static Object^ WaitForValue( 
   IEasyUAClient^ client,
   UAAttributeArguments^ attributeArguments
)

Parameters

client

The client object that will perform the operation.

This is typically the OpcLabs.EasyOpc.UA.EasyUAClient object.

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

attributeArguments

Holds all arguments needed to specify a node together with its attribute in an OPC-UA server.

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

Return Value

If successful, the function returns the actual value of node&attribute requested.

This method can return 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.
OpcLabs.EasyOpc.UA.OperationModel.UAException	The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause. This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

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.

OpcLabs.EasyOpc.UA.OperationModel.UAException

The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause.

This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

Remarks

The WaitForValue methods subscribe to the specified node&attribute, and monitor its data until it has "good" status severity, an error occurs, or the alloted time elapses.

This is an extension method (info: C#, VB.NET). In languages that have support for extensions methods (such as C# and VB.NET), you can use the extension method as if it were a regular method on the object that is its first parameter. In other languages (such as with Python.NET), you will call the extension as a static method, and pass it the object on which it acts as its first parameter.

Example

CSharp
VB.NET
Python

// This example shows how to wait on an item until a value with "good" status severity becomes available.
//
// 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 OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.Extensions;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClientExtension
{
    class WaitForValue
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object
            var client = new EasyUAClient();

            Console.WriteLine("Waiting until an item value with \"good\" status severity becomes available...");
            object value;
            try
            {
                value = client.WaitForValue(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10221",
                    monitoringParameters: 100,  // this is the sampling rate
                    millisecondsTimeout: 60*1000);
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Display the obtained value.
            Console.WriteLine("value: {0}", value);
        }
    }
}

' This example shows how to wait on an item until a value with "good" status severity becomes available.
'
' 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 Opc.Ua
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.Extensions
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _EasyUAClientExtension
    Friend Class WaitForValue
        Public Shared Sub Main1()

            ' Define which server we will work with.
            Dim endpointDescriptor As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object
            Dim client = New EasyUAClient()

            Console.WriteLine("Waiting until an item value with ""good"" status severity becomes available...")
            Dim value As Object
            Try
                value = client.WaitForValue(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10221",
                    monitoringParameters:=100,  ' this is the sampling rate
                    millisecondsTimeout:=60 * 1000)
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display the obtained value.
            Console.WriteLine("value: {0}", value)
        End Sub
    End Class
End Namespace

# This example shows how to wait on an item until a value with "good" status severity becomes available.
#
# 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.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.Extensions import *
from OpcLabs.EasyOpc.UA.OperationModel import *


endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'

# Instantiate the client object.
client = EasyUAClient()

print('Waiting until an item value with "good" status severity becomes available...')
try:
    value = IEasyUAClientExtension2.WaitForValue(client,
                                                 endpointDescriptor,
                                                 UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10221'),
                                                 UAMonitoringParameters(100),   # this is the sampling rate
                                                 60*1000)   # millisecondsTimeout
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display the obtained value.
print('value: ', value, sep='')

print()
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

IEasyUAClientExtension2 Class
IEasyUAClientExtension2 Members
Overload List

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Missing some example? Ask us for it on our Online Forums! You do not have to own a commercial license in order to use Online Forums, and we reply to every post.