QuickOPC User's Guide and Reference
ReadItem(IEasyDAClient,DAItemArguments,DAReadParameters) Method
Example 



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OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.DataAccess Namespace > IEasyDAClientExtension Class > ReadItem Method : ReadItem(IEasyDAClient,DAItemArguments,DAReadParameters) Method
The client object that will perform the operation.
Holds an OPC server and item descriptor.
The read parameters (such as data source or value age).
Reads a named item from an OPC server. Value, quality and timestamp are returned. Reads a named item using an item arguments objects, and read parameters.
Syntax
'Declaration
 

<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadItem( _
   ByVal client As IEasyDAClient, _
   ByVal itemArguments As DAItemArguments, _
   ByVal readParameters As DAReadParameters _
) As DAVtq
 
'Usage
 

Dim client As IEasyDAClient
Dim itemArguments As DAItemArguments
Dim readParameters As DAReadParameters
Dim value As DAVtq
 
value = IEasyDAClientExtension.ReadItem(client, itemArguments, readParameters)

Parameters

client
The client object that will perform the operation.
itemArguments
Holds an OPC server and item descriptor.
readParameters
The read parameters (such as data source or value age).

Return Value

If successful, the function returns a DAVtq object. The object contains the value, timestamp and quality of the OPC item requested.
Exceptions
ExceptionDescription
OpcLabs.EasyOpc.OperationModel.OpcExceptionThrown when the OPC operation fails.
System.ArgumentNullExceptionA null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.
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.

The ReadItem method only waits for the first update from the server (or until the timeout elapses); it does not wait until the quality becomes "uncertain" or "good".

Example
// This example shows how to read a single item, and display its value, timestamp and quality.

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

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

            DAVtq vtq;
            try
            {
                vtq = client.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random");
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            Console.WriteLine("Vtq: {0}", vtq);
        }
    }
}
// Shows how different data types can be read, including rare types and arrays of values.

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

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadItem
    {
        // Instantiate the client object.
        static readonly EasyDAClient Client = new EasyDAClient();

        static void ReadAndDisplay(string itemId)
        {
            Console.WriteLine();
            Console.WriteLine("Reading \"{0}\"...", itemId);

            DAVtq vtq;
            try
            {
                vtq = Client.ReadItem("OPCLabs.KitServer.2", itemId);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }
            Console.WriteLine("Vtq: {0}", vtq);
        }

        public static void DataTypes()
        {
            ReadAndDisplay("Simulation.Register_EMPTY");
            ReadAndDisplay("Simulation.Register_NULL");
            ReadAndDisplay("Simulation.Register_DISPATCH");

            ReadAndDisplay("Simulation.ReadValue_I2");
            ReadAndDisplay("Simulation.ReadValue_I4");
            ReadAndDisplay("Simulation.ReadValue_R4");
            ReadAndDisplay("Simulation.ReadValue_R8");
            ReadAndDisplay("Simulation.ReadValue_CY");
            ReadAndDisplay("Simulation.ReadValue_DATE");
            ReadAndDisplay("Simulation.ReadValue_BSTR");
            ReadAndDisplay("Simulation.ReadValue_BOOL");
            ReadAndDisplay("Simulation.ReadValue_DECIMAL");
            ReadAndDisplay("Simulation.ReadValue_I1");
            ReadAndDisplay("Simulation.ReadValue_UI1");
            ReadAndDisplay("Simulation.ReadValue_UI2");
            ReadAndDisplay("Simulation.ReadValue_UI4");
            ReadAndDisplay("Simulation.ReadValue_INT");
            ReadAndDisplay("Simulation.ReadValue_UINT");

            ReadAndDisplay("Simulation.ReadValue_ArrayOfI2");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfI4");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfR4");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfR8");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfCY");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfDATE");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfBSTR");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfBOOL");
            //ReadAndDisplay("Simulation.ReadValue_ArrayOfDECIMAL");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfI1");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfUI1");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfUI2");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfUI4");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfINT");
            ReadAndDisplay("Simulation.ReadValue_ArrayOfUINT");
        }
    }
}
Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2012, Windows Server 2016; .NET Core, .NET 5, .NET 6: Linux, macOS, Microsoft Windows

See Also

Reference

IEasyDAClientExtension Class
IEasyDAClientExtension Members
Overload List

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