PullServerConditionChanged Method (_EasyUAClientConnectionMonitoring)

Attempts to pull an OPC server condition changed event.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<CanBeNullAttribute()>
Function PullServerConditionChanged( _
   ByVal millisecondsTimeout As Integer _
) As EasyUAServerConditionChangedEventArgs

'Usage
 
Dim instance As _EasyUAClientConnectionMonitoring
Dim millisecondsTimeout As Integer
Dim value As EasyUAServerConditionChangedEventArgs
 
value = instance.PullServerConditionChanged(millisecondsTimeout)

[CanBeNull()]
EasyUAServerConditionChangedEventArgs PullServerConditionChanged( 
   int millisecondsTimeout
)

[CanBeNull()]
EasyUAServerConditionChangedEventArgs^ PullServerConditionChanged( 
   int millisecondsTimeout
)

Parameters

millisecondsTimeout: The number of milliseconds to wait, or System.Threading.Timeout.Infinite (-1) to wait indefinitely.

Return Value

The event arguments, or null if no event is available within the specified time.

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.

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.

Example

COM

VBScript

Rem This example shows how to monitor connections to and disconnections from the OPC UA server with event pull mechanism.

Option Explicit

' Instantiate the client object.
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")

' Obtain the client connection monitoring service.
Dim ClientConnectionMonitoring: Set ClientConnectionMonitoring = Client.GetServiceByName("OpcLabs.EasyOpc.UA.Services.IEasyUAClientConnectionMonitoring, OpcLabs.EasyOpcUA")
If ClientConnectionMonitoring Is Nothing Then
    WScript.Echo "The client connection monitoring service is not available."
    WScript.Quit
End If

' In order to use event pull, you must set a non-zero queue capacity upfront.
ClientConnectionMonitoring.PullServerConditionChangedQueueCapacity = 1000

WScript.Echo "Reading (1)"
' The first read will cause a connection to the server.
Dim AttributeData1: Set AttributeData1 = Client.Read("opc.tcp://opcua.demo-this.com:51210/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853")
WScript.Echo AttributeData1

WScript.Echo "Reading (2)"
' The second read, because it closely follows the first one, will reuse the connection that is already open.
Dim AttributeData2: Set AttributeData2 = Client.Read("opc.tcp://opcua.demo-this.com:51210/UA/SampleServer", "nsu=http://test.org/UA/Data/ ;i=10853")
WScript.Echo AttributeData2

WScript.Echo "Processing server condition changed events for 10 seconds..."
' Because we only started the processing after we have made the reads, there are now events related to opening the 
' connection already in the queue, and they will be consumed first.
' Since the connection is now not used for some time, it will be closed.
Dim endTime: endTime = Now() + 10*(1/24/60/60)
Do
    Dim EventArgs: Set EventArgs = ClientConnectionMonitoring.PullServerConditionChanged(2*1000)
    If Not (EventArgs Is Nothing) Then
        ' Handle the server condition changed event.
        WScript.Echo EventArgs
    End If    
Loop While Now() < endTime

WScript.Echo "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

_EasyUAClientConnectionMonitoring Interface
_EasyUAClientConnectionMonitoring Members

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