ValueSymbolExtensions.WhenValueChanged Method (IAdsConnection, IEnumerable.ISymbol.)

C#

public static IObservable<Object> WhenValueChanged(
    this IAdsConnection connection,
    IEnumerable<ISymbol> symbols
)

Parameters

Return Value

Type: IObservable.Object.
IObservable<ValueChangedArgs>.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IAdsConnection. 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).

Examples

The same for more than one IValueSymbol.

Observe changing ADS Symbols (ADS Notifications)

// 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.CycleCount"]; // UShort Type
    IValueSymbol lastExecTime = (IValueSymbol)symbolLoader.Symbols["TwinCAT_SystemInfoVarList._TaskInfo.LastExecTime"]; // UInt Type

    SymbolCollection symbols = new SymbolCollection();
    symbols.Add(cycleCount);
    symbols.Add(lastExecTime);

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

    cycleCount.NotificationSettings = new NotificationSettings(AdsTransMode.OnChange,500,5000); // optional: Change NotificationSettings on Symbol

    // Turning ADS Notifications into sequences of Value Objects (Taking 20 Values)
    // and subscribe to them.
    IDisposable subscription = client.WhenValueChanged(symbols).Take(20).Subscribe(valueObserver);

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

Examples

The following sample shows how to observe Value changed Notifications with the reactive ValueSymbolExtensions from an DynamicSymbol.

Observe a single changing ADS Symbol (ADS Notifications) with the dynamic language runtime (.NET DLR)

// 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()));
    }
    );

    cycleCount.NotificationSettings = new NotificationSettings(AdsTransMode.OnChange, 500, 5000); // optional: Change NotificationSettings on Symbol

    // Turning ADS Notifications into sequences of Value Objects (Taking 20 Values)
    // and subscribe to them.
    IDisposable subscription = cycleCount.WhenValueChanged().Take(20).Subscribe(valueObserver);

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

Reference

ValueSymbolExtensions Class

WhenValueChanged Overload

TwinCAT.Ads.Reactive Namespace

Observable