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



OpcLabs.EasyOpcClassic Assembly > OpcLabs.EasyOpc.DataAccess.Extensions Namespace > IEasyDAClientExtension2 Class > WaitForItemValue Method : WaitForItemValue(IEasyDAClient,DAItemArguments) Method
The client object that will perform the operation.
Holds an OPC server and item descriptor.
Subscribes to the specified OPC-DA item, and monitors its data until it has "good" quality, an error occurs, or the alloted time elapses.
Syntax
'Declaration
 
<ExtensionAttribute()>
<CanBeNullAttribute()>
Public Overloads Shared Function WaitForItemValue( _
   ByVal client As IEasyDAClient, _
   ByVal itemArguments As DAItemArguments _
) As Object
'Usage
 
Dim client As IEasyDAClient
Dim itemArguments As DAItemArguments
Dim value As Object
 
value = IEasyDAClientExtension2.WaitForItemValue(client, itemArguments)
[Extension()]
[CanBeNull()]
public static object WaitForItemValue( 
   IEasyDAClient client,
   DAItemArguments itemArguments
)
[Extension()]
[CanBeNull()]
public:
static Object^ WaitForItemValue( 
   IEasyDAClient^ client,
   DAItemArguments^ itemArguments
) 

Parameters

client
The client object that will perform the operation.
itemArguments
Holds an OPC server and item descriptor.

Return Value

If successful, the function returns the actual value of OPC item requested.
Exceptions
ExceptionDescription
The OPC "Classic" (or OPC XML-DA) operation has failed.
A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.
Example
// This example shows how to wait on an item until a value with "good" quality becomes available.

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

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

            Console.WriteLine("Waiting until an item value with \"good\" quality becomes available...");
            object value;
            try
            {
                value = client.WaitForItemValue("", "OPCLabs.KitServer.2", "Demo.Unreliable", 
                    groupParameters: 100,   // this is the requested update rate
                    millisecondsTimeout: 60*1000);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            // Display the obtained item value.
            Console.WriteLine($"value: {value}");
        }
    }
}
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

IEasyDAClientExtension2 Class
IEasyDAClientExtension2 Members
Overload List