FindLocalApplications Method (

Discovers available OPC-UA applications, specifying the discovery URI strings, and application types.

Discovers available OPC-UA applications, using the specified discovery URI strings.

This method discovers available OPC-UA applications and returns information about them, using the specified discovery URI strings and filtering by specified application types. It uses the discovery services on specified discovery endpoints.

Invokes the FindServers service.

The discovery may be attempted in parallel on the specified endpoints, depending on component settings.

See also in Knowledge Base: Technical note-OPC UA Discovery in QuickOPC.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<NotNullAttribute()>
Function FindLocalApplications( _
   ByVal discoveryUriStringArray As Object, _
   ByVal applicationTypes As UAApplicationTypes _
) As UADiscoveryElementCollection

'Usage
 
Dim instance As _EasyUAClient
Dim discoveryUriStringArray As Object
Dim applicationTypes As UAApplicationTypes
Dim value As UADiscoveryElementCollection
 
value = instance.FindLocalApplications(discoveryUriStringArray, applicationTypes)

[NotNull()]
UADiscoveryElementCollection FindLocalApplications( 
   object discoveryUriStringArray,
   UAApplicationTypes applicationTypes
)

[NotNull()]
UADiscoveryElementCollection^ FindLocalApplications( 
   Object^ discoveryUriStringArray,
   UAApplicationTypes applicationTypes
)

Parameters

discoveryUriStringArray: The value of this parameter cannot be null (Nothing in Visual Basic).
applicationTypes: Application types to be discovered.

Return Value

Returns a collection of application elements (servers, OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement).

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

The individual elements of the returned value are never 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

This member or type is for use from COM. It is not meant to be used from .NET or Python. Refer to the corresponding .NET member or type instead, if you are developing in .NET or Python.

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.

Invokes the FindServers service.

The discovery may be attempted in parallel on the specified endpoints, depending on component settings.

See also in Knowledge Base: Technical note-OPC UA Discovery in QuickOPC.

Example

// This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in Object Pascal (Delphi) on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-OP .
// 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.

class procedure FindLocalApplications.Main;
const
  UAApplicationTypes_Server = 1;
var
  Client: OpcLabs_EasyOpcUA_TLB._EasyUAClient;
  Count: Cardinal;
  Element: OleVariant;
  DiscoveryElement: _UADiscoveryElement;
  DiscoveryElementEnumerator: IEnumVariant;
  DiscoveryElements: _UADiscoveryElementCollection;
  DiscoveryUriStrings: OleVariant;
begin
  DiscoveryUriStrings := VarArrayCreate([0, 2], varVariant);
  DiscoveryUriStrings[0] := 'opc.tcp://opcua.demo-this.com:4840/UADiscovery';
  DiscoveryUriStrings[1] := 'http://opcua.demo-this.com/UADiscovery/Default.svc';
  DiscoveryUriStrings[2] := 'http://opcua.demo-this.com:52601/UADiscovery';

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

  // Obtain collection of application elements
  try
    DiscoveryElements := Client.FindLocalApplications(DiscoveryUriStrings, UAApplicationTypes_Server);
  except
    on E: EOleException do
    begin
      WriteLn(Format('*** Failure: %s', [E.GetBaseException.Message]));
      Exit;
    end;
  end;

  // Display results
  DiscoveryElementEnumerator := DiscoveryElements.GetEnumerator;
  while (DiscoveryElementEnumerator.Next(1, Element, Count) = S_OK) do
  begin
    DiscoveryElement := IUnknown(Element) as _UADiscoveryElement;
    WriteLn(
      'DiscoveryElements["',
      DiscoveryElement.DiscoveryUriString,
      '".ApplicationUriString: ',
      DiscoveryElement.ApplicationUriString);
  end;

  VarClear(DiscoveryUriStrings);
end;

REM This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
REM
REM Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
REM OPC client and subscriber examples in Visual Basic on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VB .
REM Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
REM a commercial license in order to use Online Forums, and we reply to every post.

Public Sub FindLocalApplications_Main_Command_Click()
    OutputText = ""
    
    Dim DiscoveryUriStrings(2)
    DiscoveryUriStrings(0) = "opc.tcp://opcua.demo-this.com:4840/UADiscovery"
    DiscoveryUriStrings(1) = "http://opcua.demo-this.com/UADiscovery/Default.svc"
    DiscoveryUriStrings(2) = "http://opcua.demo-this.com:52601/UADiscovery"

    ' Instantiate the client object
    Dim Client As New EasyUAClient

    ' Obtain collection of application elements
    On Error Resume Next
    Dim DiscoveryElementCollection As UADiscoveryElementCollection
    Set DiscoveryElementCollection = Client.FindLocalApplications(DiscoveryUriStrings, UAApplicationTypes_Server)
    If Err.Number <> 0 Then
        OutputText = OutputText & "*** Failure: " & Err.Source & ": " & Err.Description & vbCrLf
        Exit Sub
    End If
    On Error GoTo 0
    
    ' Display results
    Dim DiscoveryElement As UADiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
        OutputText = OutputText & "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
            DiscoveryElement.applicationUriString & vbCrLf
    Next
End Sub

Rem This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Const UAApplicationTypes_Server = 1

Dim discoveryUriStrings(2)
discoveryUriStrings(0) = "opc.tcp://opcua.demo-this.com:4840/UADiscovery"
discoveryUriStrings(1) = "http://opcua.demo-this.com/UADiscovery/Default.svc"
discoveryUriStrings(2) = "http://opcua.demo-this.com:52601/UADiscovery"

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

' Obtain collection of application elements
On Error Resume Next
Dim DiscoveryElementCollection: Set DiscoveryElementCollection = Client.FindLocalApplications(discoveryUriStrings, UAApplicationTypes_Server)
If Err.Number <> 0 Then
    WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
    WScript.Quit
End If
On Error Goto 0

' Display results
Dim DiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
    WScript.Echo "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
        DiscoveryElement.ApplicationUriString
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

_EasyUAClient Interface
_EasyUAClient Members

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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.