Observables Usage

Table of Contents

• About
• Usage
• Further Reading

About

An interface can declare an observable object. This observable will notify observers (callback functions) when a certain event occurs.

Usage

This interface declares the observable "ObservablePing" that will notify observers when the function "Ping" is called:

// This example shows an interface declaring an observable.
namespace maxon
{
 
class ObserveMeInterface : MAXON_INTERFACE_BASES(maxon::ObserverObjectInterface)
{
  MAXON_INTERFACE(ObserveMeInterface, MAXON_REFERENCE_NORMAL, "net.maxonexample.interfaces.observeme");
 
public:
  //----------------------------------------------------------------------------------------
  // Function makes "Ping".
  //----------------------------------------------------------------------------------------
  MAXON_METHOD void Ping();
 
  //----------------------------------------------------------------------------------------
  // Signal fired when Ping() is called.
  //----------------------------------------------------------------------------------------
  MAXON_OBSERVABLE(Result<void>, ObservablePing, (maxon::Int32 count), maxon::ObservableCombinerRunAllComponent);
};
}

Such a callback function must have the same return value and argument list as defined in the observable declaration:

// This example shows a function that can be used as an observer.
 
static maxon::Result<void> WatchPing(maxon::Int count)
{
  DiagnosticOutput("Count: @", count);
  return maxon::OK;
}

The observable is accessible by the function of its name. An observer is added with maxon::ObservableBaseInterface::AddObserver():

  // This example adds an observer to the "ObservablePing" observable.
 
  g_observeMe.ObservablePing(true).AddObserver(WatchPing) iferr_return;

It is also possible to add lambdas to the observable.

  // This example adds a lambda to the "ObservablePing" observable.
 
  g_observeMe.ObservablePing(true).AddObserver(
    [](maxon::Int count)
    {
      DiagnosticOutput("Count: @", count);
      return maxon::OK;
    }) iferr_return;

The observer functions are called when the specific event is triggered.

    // This example calls the Ping() function which will notify all registered observers.
 
    g_observeMe.Ping();

Further Reading

• Observables
• Observables Declaration
• Observables Implementation