WaitForValue(IEasyUAClient,UAAttributeArguments,UAMonitoringParameters,Int32) Method

Subscribes to the specified node&attribute, and monitors its data until it has "good" status severity, an error occurs, or the alloted time elapses.

Syntax

Visual Basic
C#
C++/CLI

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

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

[Extension()]
[CanBeNull()]
public static object WaitForValue( 
   IEasyUAClient client,
   UAAttributeArguments attributeArguments,
   UAMonitoringParameters monitoringParameters,
   int millisecondsTimeout
)

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

Parameters

client: The client object that will perform the operation.
attributeArguments: Holds all arguments needed to specify a node together with its attribute in an OPC-UA server.
monitoringParameters: Contains monitoring parameters (such as the sampling interval, and optional data change or event filter).
millisecondsTimeout: The number of milliseconds to wait, or System.Threading.Timeout.Infinite to wait indefinitely.

Return Value

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

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.ArgumentOutOfRangeException	The value of an argument is outside the allowable range of values as defined by the invoked method. 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.

System.ArgumentOutOfRangeException

The value of an argument is outside the allowable range of values as defined by the invoked method.

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.

Example

// This example shows how to wait on an item until a value with "good" status severity becomes available.

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.

# 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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