Observables Usage

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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.
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(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 void WatchPing(maxon::Int count)
{
DiagnosticOutput("Count: @", count);
}

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().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().AddObserver(
[](maxon::Int count)
{
DiagnosticOutput("Count: @", count);

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