WriteItemValue(IEasyDAClient,String,String,String,Object,VarType) Method

Writes a value into a named item in an OPC server. Only the item value is written (quality and timestamp are not written). Writes a value into a named item using individual parameters specifying its location, and a specific data type.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
Public Overloads Shared Sub WriteItemValue( _
   ByVal client As IEasyDAClient, _
   ByVal machineName As String, _
   ByVal serverClass As String, _
   ByVal itemId As String, _
   ByVal value As Object, _
   ByVal dataType As VarType _
)

'Usage
 
Dim client As IEasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim value As Object
Dim dataType As VarType
 
IEasyDAClientExtension.WriteItemValue(client, machineName, serverClass, itemId, value, dataType)

[Extension()]
public static void WriteItemValue( 
   IEasyDAClient client,
   string machineName,
   string serverClass,
   string itemId,
   object value,
   VarType dataType
)

[Extension()]
public:
static void WriteItemValue( 
   IEasyDAClient^ client,
   String^ machineName,
   String^ serverClass,
   String^ itemId,
   Object^ value,
   VarType^ dataType
)

Parameters

client: The client object that will perform the operation.
machineName: Name of the machine. Determines the computer on which the OPC server is located. May be an empty string, in which case the OPC server is assumed to exist on the local computer or at the computer specified for it by DCOM configuration.
serverClass: Contains ProgID of the OPC server to write into.
itemId: Contains OPC item identifier.
value: The value to be written.
dataType: Specifies the data type. Passing OpcLabs.BaseLib.ComInterop.VarTypes.Empty will cause the value be written using server's canonical data type.

Exceptions

Exception Description

Exception	Description
System.ArgumentException	One of the arguments provided to a method is not valid. 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.
OpcLabs.EasyOpc.OperationModel.OpcException	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.

System.ArgumentException

One of the arguments provided to a method is not valid.

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.

OpcLabs.EasyOpc.OperationModel.OpcException

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 can be local or can be remotely accessed via DCOM. Optionally, an access path can be specified or a specific data type can be requested.

Example

// This example shows how to write a value into a single item, specifying its requested data type.

using System;
using OpcLabs.BaseLib.ComInterop;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.OperationModel;

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

            try
            {
                client.WriteItemValue("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 12345,
                    VarTypes.I4);   // <-- the requested data type
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
            }
        }
    }
}

# This example shows how to write a value into a single item, specifying its requested data type.

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.BaseLib.ComInterop import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

# Perform the operation
try:
    IEasyDAClientExtension.WriteItemValue(client, '', 'OPCLabs.KitServer.2', 'Simulation.Register_I4', 12345,
                                          VarType(VarTypes.I4)) # <-- the requested data type
except OpcException as opcException:
    print('*** Failure: ' + opcException.GetBaseException().Message)
    exit()

print('Finished.')

' This example shows how to write a value into a single item, specifying its requested data type.

Imports OpcLabs.BaseLib.ComInterop
Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class WriteItemValue
        Public Shared Sub RequestedDataType()
            Dim client = New EasyDAClient()

            Try
                client.WriteItemValue("", "OPCLabs.KitServer.2", "Simulation.Register_I4", 12345,
                                      VarTypes.I4) ' <-- the requested data type
            Catch opcException As OpcException
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
                Exit Sub
            End Try
        End Sub
    End Class
End Namespace

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

IEasyDAClientExtension Class
IEasyDAClientExtension Members
Overload List

Send Documentation Feedback. Resources: Knowledge Base. Technical support: Online Forums, FAQ.