ValueSymbolExtensionsPollValues(IValueSymbol, TimeSpan, Boolean) Method

C#

public static IObservable<Object?> PollValues(
    this IValueSymbol symbol,
    TimeSpan period,
    bool ignoreErrors
)

Parameters

Return Value

IObservable Object
IObservable<System.Object>.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IValueSymbol. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

Remarks

If ignoreErrors is not set and ReadRequest errors occur, the observable will be closed with error (AdsException)./> If errors are ignored, the observable will return NULL values on erroneous requests.

Example

Here, the values are polled in a specific time period and sequential Reads are triggered (in opposite to ADS Notification in the latter example)

Observe changing ADS Symbols (Read Polling)

// To Test the Observer run a project on the local PLC System (Port 851)
using (AdsClient client = new AdsClient())
{
    // Connect to target
    client.Connect(new AmsAddress(AmsNetId.Local, 851));

    // Create Symbol information
    var symbolLoader = SymbolLoaderFactory.Create(client, SymbolLoaderSettings.Default);
    IValueSymbol cycleCount = (IValueSymbol)symbolLoader.Symbols["TwinCAT_SystemInfoVarList._TaskInfo[1].CycleCount"];

    // Reactive Notification Handler
    var valueObserver = Observer.Create<object>(val =>
    {
    Console.WriteLine(string.Format("Instance: {0}, Value: {1}", cycleCount.InstancePath, val.ToString()));
    }
    );

    // Take 20 Values in an Interval of 500ms
    IDisposable subscription = cycleCount.PollValues(TimeSpan.FromMilliseconds(500)).Take(20).Subscribe(valueObserver);

    Console.ReadKey(); // Wait for Key press
    subscription.Dispose(); // Dispose the Subscription
}

Reference

ValueSymbolExtensions Class PollValues Overload TwinCAT.Ads.Reactive Namespace PollValues(IValueSymbol, IObservableUnit, Boolean) PollValues(IValueSymbol, TimeSpan)

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