OPC Studio User's Guide and Reference
BrowseNodes Method (EasyDAClientCore)
Example 



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OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.DataAccess Namespace > EasyDAClientCore Class : BrowseNodes Method
The OPC server involved in the operation.

Because the OpcLabs.EasyOpc.ServerDescriptor has an implicit conversion from System.Guid, System.String and OpcLabs.EasyOpc.ServerElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a GUID (representing the CLSID of the server), a string (representing the so-called OPC server descriptor string, such as a ProgID or the URL of the server), or a OpcLabs.EasyOpc.ServerElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC server descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.ServerDescriptor.FromGuid, OpcLabs.EasyOpc.ServerDescriptor.FromString or OpcLabs.EasyOpc.ServerDescriptor.FromServerElement static method instead.

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

Descriptor for the parent branch to be browsed (can be the root).

Because the DANodeDescriptor has an implicit conversion from System.String and OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the qualified name of the node), or a OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC DA node descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the DANodeDescriptor.FromString or DANodeDescriptor.FromDANodeElement static method instead.

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

Contains filtering conditions.

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

Browses the specified branch (or root) in OPC server's address space, and returns information about child nodes (both branches and leaves) found. Specify server descriptor, parent item ID, and node filter.
Syntax
'Declaration
 
Public Function BrowseNodes( _
   ByVal serverDescriptor As ServerDescriptor, _
   ByVal parentNodeDescriptor As DANodeDescriptor, _
   ByVal browseParameters As DABrowseParameters _
) As DANodeElementCollection
 
'Usage
 
Dim instance As EasyDAClientCore
Dim serverDescriptor As ServerDescriptor
Dim parentNodeDescriptor As DANodeDescriptor
Dim browseParameters As DABrowseParameters
Dim value As DANodeElementCollection
 
value = instance.BrowseNodes(serverDescriptor, parentNodeDescriptor, browseParameters)

Parameters

serverDescriptor
The OPC server involved in the operation.

Because the OpcLabs.EasyOpc.ServerDescriptor has an implicit conversion from System.Guid, System.String and OpcLabs.EasyOpc.ServerElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a GUID (representing the CLSID of the server), a string (representing the so-called OPC server descriptor string, such as a ProgID or the URL of the server), or a OpcLabs.EasyOpc.ServerElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC server descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.ServerDescriptor.FromGuid, OpcLabs.EasyOpc.ServerDescriptor.FromString or OpcLabs.EasyOpc.ServerDescriptor.FromServerElement static method instead.

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

parentNodeDescriptor
Descriptor for the parent branch to be browsed (can be the root).

Because the DANodeDescriptor has an implicit conversion from System.String and OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the qualified name of the node), or a OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC DA node descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the DANodeDescriptor.FromString or DANodeDescriptor.FromDANodeElement static method instead.

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

browseParameters
Contains filtering conditions.

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

Return Value

The method returns a keyed collection of OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement values, each containing information about a particular node found. The keys of the keyed collection are the names of the nodes.

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

The individual elements of the returned value are never null (Nothing in Visual Basic).

This return value of this method should not be ignored.

Exceptions
ExceptionDescription

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.

An operation was performed on a disposed object.

The OPC "Classic" (or OPC XML-DA) 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 server(s) can be local or can be remotely accessed via DCOM.

Example
// This example shows how to obtain all nodes under the "Simulation" branch of the address space. For each node, it displays
// whether the node is a branch or a leaf.
//
// 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.DataAccess;
using OpcLabs.EasyOpc.DataAccess.AddressSpace;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class BrowseNodes
    {
        public static void Main1()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            DANodeElementCollection nodeElements;
            try
            {
                nodeElements = client.BrowseNodes("", "OPCLabs.KitServer.2", "Greenhouse", DABrowseParameters.Default);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine($"*** Failure: {opcException.GetBaseException().Message}");
                return;
            }

            foreach (DANodeElement nodeElement in nodeElements)
            {
                Console.WriteLine($"NodeElements(\"{nodeElement.Name}\"):");
                Console.WriteLine($"    .IsBranch: {nodeElement.IsBranch}");
                Console.WriteLine($"    .IsLeaf: {nodeElement.IsLeaf}");
            }
        }
    }
}
// This example shows how to obtain data types of leaves in the OPC-DA address 
// space by browsing and filtering, i.e. without the use of OPC properties. 
// This technique allows determining the data types with servers that only 
// support OPC-DA 1.0. It can also be more effective than the use of 
// GetMultiplePropertyValues, if there is large number of leaves, and 
// relatively small number of data types to be checked.
//
// 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.Collections.Generic;
using OpcLabs.BaseLib.ComInterop;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.AddressSpace;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class BrowseNodes
    {
        public static void DataTypes()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            // Define the list of data types we will be checking for. 
            // Change as needed for your application.
            // This technique is only usable if there is a known list of 
            // data types you are interested in. If you are interested in 
            // all leaves, even those that are of data types not explicitly 
            // listed, always include VarTypes.Empty as the first data type. 
            // The leaves of "unlisted" data types will have VarTypes.Empty 
            // associated with them.
            var dataTypes = new VarType[] { VarTypes.Empty, VarTypes.I2, VarTypes.R4 };

            // For each leaf found, this dictionary wil hold its associated data type.
            var dataTypeDictionary = new Dictionary<DANodeElement, VarType>();

            // For each data type, browse for leaves of this data type.
            foreach (VarType dataType in dataTypes)
            {
                var browseParameters = new DABrowseParameters(DABrowseFilter.Leaves, "", "", dataType);
                DANodeElementCollection nodeElements;
                try
                {
                    nodeElements = client.BrowseNodes("", "OPCLabs.KitServer.2", "Greenhouse", browseParameters);
                }
                catch (OpcException opcException)
                {
                    Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                    return;
                }

                // Store the leaf information into the dictionary, and 
                // associate the current data type with it.
                foreach (var nodeElement in nodeElements)
                    dataTypeDictionary[nodeElement] = dataType;
            }

            // Display each leaf found, and its associated data type.
            foreach (KeyValuePair<DANodeElement, VarType> pair in dataTypeDictionary)
            {
                DANodeElement nodeElement = pair.Key;
                VarType dataType = pair.Value;
                Console.WriteLine("{0}: {1}", nodeElement, dataType);
            }
        }
    }
}
// This example shows how to recursively browse the nodes in the OPC address space.
//
// 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.Diagnostics;
using OpcLabs.EasyOpc;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.AddressSpace;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class BrowseNodes
    {
        public static void Recursive()
        {
            var stopwatch = new Stopwatch();
            stopwatch.Start();

            // Instantiate the client object.
            var client = new EasyDAClient();
            _branchCount = 0;
            _leafCount = 0;

            try
            {
                BrowseFromNode(client, "OPCLabs.KitServer.2", "");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            stopwatch.Stop();
            Console.WriteLine("Browsing has taken (milliseconds): {0}", stopwatch.ElapsedMilliseconds);
            Console.WriteLine("Branch count: {0}", _branchCount);
            Console.WriteLine("Leaf count: {0}", _leafCount);
        }

        private static void BrowseFromNode(
            EasyDAClient client,
            ServerDescriptor serverDescriptor,
            DANodeDescriptor parentNodeDescriptor)
        {
            Debug.Assert(client != null);
            Debug.Assert(serverDescriptor != null);
            Debug.Assert(parentNodeDescriptor != null);

            // Obtain all node elements under parentNodeDescriptor
            var browseParameters = new DABrowseParameters();    // no filtering whatsoever
            DANodeElementCollection nodeElementCollection =
                client.BrowseNodes(serverDescriptor, parentNodeDescriptor, browseParameters);
            // Remark: that BrowseNodes(...) may also throw OpcException; a production code should contain handling for 
            // it, here omitted for brevity.

            foreach (DANodeElement nodeElement in nodeElementCollection)
            {
                Debug.Assert(nodeElement != null);

                Console.WriteLine(nodeElement);

                // If the node is a branch, browse recursively into it.
                if (nodeElement.IsBranch)
                {
                    _branchCount++;
                    BrowseFromNode(client, serverDescriptor, nodeElement);
                }
                else
                {
                    _leafCount++;
                }
            }
        }

        private static int _branchCount;
        private static int _leafCount;
    }
}
// Recursively browses and displays the nodes in the OPC address space, and attempts to read and display values of all OPC 
// items it finds.
//
// 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.Diagnostics;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.AddressSpace;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class BrowseNodes
    {
        const string ServerClass = "OPCLabs.KitServer.2";

        // Instantiate the client object.
        static readonly EasyDAClient Client = new EasyDAClient();

        static void BrowseAndReadFromNode(string parentItemId)
        {
            // Obtain all node elements under parentItemId
            var browseParameters = new DABrowseParameters(); // no filtering whatsoever
            DANodeElementCollection nodeElementCollection = Client.BrowseNodes("", ServerClass, parentItemId,
                browseParameters);
            // Remark: that BrowseNodes(...) may also throw OpcException; a production code should contain handling for it, here 
            // omitted for brevity.

            foreach (DANodeElement nodeElement in nodeElementCollection)
            {
                Debug.Assert(nodeElement != null);

                // If the node is a leaf, it might be possible to read from it
                if (nodeElement.IsLeaf)
                {
                    // Determine what the display - either the value read, or exception message in case of failure.
                    string display;
                    try
                    {
                        object value = Client.ReadItemValue("", ServerClass, nodeElement);
                        display = $"{value}";
                    }
                    catch (OpcException exception)
                    {
                        display = $"** {exception.GetBaseException().Message} **";
                    }

                    Console.WriteLine("{0} -> {1}", nodeElement.ItemId, display);
                }
                // If the node is not a leaf, just display its itemId
                else
                    Console.WriteLine("{0}", nodeElement.ItemId);

                // If the node is a branch, browse recursively into it.
                if (nodeElement.IsBranch &&
                    (nodeElement.ItemId != "SimulateEvents")
                    /* this branch is too big for the purpose of this example */)
                    BrowseAndReadFromNode(nodeElement);
            }
        }

        public static void RecursiveWithRead()
        {
            Console.WriteLine("Browsing and reading values...");
            // Set timeout to only wait 1 second - default would be 1 minute to wait for good quality that may never come.
            Client.InstanceParameters.Timeouts.ReadItem = 1000;

            // Do the actual browsing and reading, starting from root of OPC address space (denoted by empty string for itemId)
            try
            {
                BrowseAndReadFromNode("");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
            }
        }
    }
}
// This example shows how to recursively browse the nodes in the OPC XML-DA address space.
//
// 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.Diagnostics;
using OpcLabs.EasyOpc;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.AddressSpace;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess.Xml
{
    class BrowseNodes
    {
        public static void RecursiveXml()
        {
            var stopwatch = new Stopwatch();
            stopwatch.Start();

            // Instantiate the client object.
            var client = new EasyDAClient();

            _branchCount = 0;
            _leafCount = 0;

            try
            {
                BrowseFromNode(client, "http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx", "");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            stopwatch.Stop();
            Console.WriteLine("Browsing has taken (milliseconds): {0}", stopwatch.ElapsedMilliseconds);
            Console.WriteLine("Branch count: {0}", _branchCount);
            Console.WriteLine("Leaf count: {0}", _leafCount);
        }

        private static void BrowseFromNode(
            EasyDAClient client,
            ServerDescriptor serverDescriptor,
            DANodeDescriptor parentNodeDescriptor)
        {
            Debug.Assert(client != null);
            Debug.Assert(serverDescriptor != null);
            Debug.Assert(parentNodeDescriptor != null);

            // Obtain all node elements under parentNodeDescriptor
            var browseParameters = new DABrowseParameters();    // no filtering whatsoever
            DANodeElementCollection nodeElementCollection =
                client.BrowseNodes(serverDescriptor, parentNodeDescriptor, browseParameters);
            // Remark: that BrowseNodes(...) may also throw OpcException; a production code should contain handling for 
            // it, here omitted for brevity.

            foreach (DANodeElement nodeElement in nodeElementCollection)
            {
                Debug.Assert(nodeElement != null);

                Console.WriteLine(nodeElement);

                // If the node is a branch, browse recursively into it.
                if (nodeElement.IsBranch)
                {
                    _branchCount++;
                    BrowseFromNode(client, serverDescriptor, nodeElement);
                }
                else
                {
                    _leafCount++;
                }
            }
        }

        private static int _branchCount;
        private static int _leafCount;
    }
}
Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

See Also