Examples - OPC Data Access - Get a value of single property

Basic example

.NET

// This example shows how to get a value of a single OPC property.
//
// Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
// case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
// IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
// also subscribe to the item in order to assure that it remains active.

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

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

            object value;
            try
            {
                value = client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random",
                    DAPropertyIds.Timestamp);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            Console.WriteLine(value);
        }
    }
}

# This example shows how to get a value of a single OPC property.
#
# Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
# case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
# IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
# also subscribe to the item in order to assure that it remains active.

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

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


# Instantiate the client object
client = EasyDAClient()

# Perform the operation
try:
    value = IEasyDAClientExtension.GetPropertyValue(client,
        '', 'OPCLabs.KitServer.2', 'Simulation.Random', DAPropertyId(DAPropertyIds.Timestamp))
except OpcException as opcException:
    print('*** Failure: ' + opcException.GetBaseException().Message)
    exit()

# Display results
print('value: ', value, sep='')

' This example shows how to get a value of a single OPC property.
'
' Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
' case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
' IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
' also subscribe to the item in order to assure that it remains active.

Imports OpcLabs.EasyOpc.DataAccess
Imports OpcLabs.EasyOpc.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class GetPropertyValue
        Public Shared Sub Main1()
            Dim client = New EasyDAClient()

            Dim value As Object
            Try
                value = client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random", DAPropertyIds.Timestamp)
            Catch opcException As OpcException
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
                Exit Sub
            End Try

            Console.WriteLine(value)
        End Sub
    End Class
End Namespace

COM

// This example shows how to get a value of a single OPC property.
//
// Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
// case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
// IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
// also subscribe to the item in order to assure that it remains active.

const Timestamp = 4;

$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");

try
{
    $value = $Client->GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random", Timestamp);
}
catch (com_exception $e)
{
    printf("*** Failure: %s\n", $e->getMessage());
    Exit();
}

printf("%s\n", $value);

# This example shows how to get a value of a single OPC property.
#
# Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
# case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
# IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
# also subscribe to the item in order to assure that it remains active.

# The Python for Windows (pywin32) extensions package is needed. Install it using "pip install pypiwin32".
# CAUTION: We now recommend using Python.NET package instead. Full set of examples with Python.NET is available!
import win32com.client
from pywintypes import com_error

TIMESTAMP = 4

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient') 

# Perform the operation
try:
    value = client.GetPropertyValue('', 'OPCLabs.KitServer.2', 'Simulation.Random', TIMESTAMP)
except com_error as e:
    print('*** Failure: ' + e.args[2][1] + ': ' + e.args[2][2])
    exit()

# Display results
print('value: ', value)

Rem This example shows how to get a value of a single OPC property.
Rem
Rem Note that some properties may not have a useful value initially (e.g. until the item is activated in a group), which also the
Rem case with Timestamp property as implemented by the demo server. This behavior is server-dependent, and normal. You can run 
Rem IEasyDAClient.ReadItemValue.Main.vbs shortly before this example, in order to obtain better property values. Your code may 
Rem also subscribe to the item in order to assure that it remains active.

Option Explicit

Const Timestamp = 4

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")

On Error Resume Next
Dim value: value = Client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random", Timestamp)
If Err.Number <> 0 Then
    WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
    WScript.Quit
End If
On Error Goto 0

WScript.Echo value

Example with time measurement

VBScript

Rem This example measures the time needed to get values of all OPC properties of a single OPC item "one by one".

Option Explicit

Dim ServerDescriptor: Set ServerDescriptor = CreateObject("OpcLabs.EasyOpc.ServerDescriptor")
ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"

Dim NodeDescriptor: Set NodeDescriptor = CreateObject("OpcLabs.EasyOpc.DataAccess.DANodeDescriptor")
NodeDescriptor.ItemID = "Simulation.ReadValue_I4"

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")

Dim PropertyElementCollection
On Error Resume Next
Set PropertyElementCollection = Client.BrowseProperties(ServerDescriptor, NodeDescriptor)
If Err.Number <> 0 Then
    WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
    WScript.Quit
End If
On Error Goto 0

'EasyDAClient.ReadItemValue "", "OPCLabs.KitServer.2", "Simulation.ReadValue_I4"
Dim startTime: startTime = Timer
Dim PropertyElement: For Each PropertyElement In PropertyElementCollection
    Dim propertyID: Set propertyID = PropertyElement.PropertyID
    On Error Resume Next
    Dim value: value = Client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.ReadValue_I4", propertyID.NumericalValue)
    If Err.Number <> 0 Then
        WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
        WScript.Quit
    End If
    On Error Goto 0
    'WScript.Echo value
Next
WScript.Echo "Time taken (milliseconds): " & (Timer - startTime)*1000

Example with type casting

The GetPropertyValue Method returns a generic object, regardless of the property involved. You may therefore need to cast the returned value to the expected type, and possibly do further processing on the value, as in the the example below.

// This example shows how to obtain a data type of an OPC item.

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

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

            // Get the value of DataType property; it is a 16-bit signed integer
            short dataType;
            try
            {
                dataType = (short)client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random",
                    DAPropertyIds.DataType);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }
            // Convert the data type to VarType
            var varType = (VarType)dataType;

            // Display the obtained data type
            Console.WriteLine("DataType: {0}", dataType);   // Display data type as numerical value
            Console.WriteLine("VarType: {0}", varType);     // Display data type symbolically

            // Code below illustrates how decisions can be made based on type
            switch (varType.InternalValue)
            {
                case VarTypes.R8:
                    Console.WriteLine("The data type is VarTypes.R8, as we expected.");
                    break;

                // other cases may come here ...

                default:
                    Console.WriteLine("The data type is not as we expected!");
                    break;
            }
        }
    }
}

# This example shows how to obtain a data type of an OPC item.

# 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()

# Get the value of DataType property; it is a 16-bit signed integer.
try:
    dataType = IEasyDAClientExtension.GetPropertyValue(client,
        '', 'OPCLabs.KitServer.2', 'Simulation.Random', DAPropertyId(DAPropertyIds.DataType))
except OpcException as opcException:
    print('*** Failure: ' + opcException.GetBaseException().Message)
    exit()
# Convert the data type to VarType.
varType = VarType(dataType)

# Display the obtained data type.
print('DataType: ', dataType, sep='')   # Display data type as numerical value
print('VarType: ', varType, sep='')     # Display data type symbolically

# Code below illustrates how decisions can be made based on type
if varType.InternalValue == VarTypes.R8:
    print('The data type is VarTypes.R8, as we expected.')
# other cases may come here ...
else:
    print('The data type is not as we expected!')

' This example shows how to obtain a data type of an OPC item.

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

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

            ' Get the value of DataType property; it is a 16-bit signed integer
            Dim aDataType As Short
            Try
                aDataType = CShort(Fix(client.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random", DAPropertyIds.DataType)))
            Catch opcException As OpcException
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
                Exit Sub
            End Try

            ' Convert the data type to VarType
            Dim varType = CType(aDataType, VarType)

            ' Display the obtained data type
            Console.WriteLine("DataType: {0}", aDataType) ' Display data type as numerical value
            Console.WriteLine("VarType: {0}", varType) ' Display data type symbolically

            ' Code below illustrates how decisions can be made based on type
            Select Case varType
                Case VarTypes.R8
                    Console.WriteLine("The data type is VarTypes.R8, as we expected.")

                    ' other cases may come here ...

                Case Else
                    Console.WriteLine("The data type is not as we expected!")
            End Select
        End Sub
    End Class
End Namespace

Examples - OPC DA Layered Extensions

Examples - OPC DA Layered Extensions - Get a record with property values

Examples - OPC DA Layered Extensions - Get data type of an item

Examples - OPC DA Layered Extensions - Get dictionary of property values

Conceptual

Getting OPC Classic Property Values