Re: Event dispatcher, hooks and Interceptor pattern for C++?
Lothar Behrens wrote:
Are there any documents available about the interceptor pattern?
I have a class that registers an event handler to be called on a given
event. The interceptor pattern then should be used to add restrictions
or other things to the function.
I could implement that in my dispatcher class (like an event
dispatcher pattern), but I think there are patterns also usable for
this issue in C++.
I have cases where I register event handlers per class and others per
instance (by adding the pointer to the event name). Thus when I have
an event handler per instance, but a interceptor
per class I have to strip the pointer from the event name (after
resolving it from the number) to locate the handler correctly.
Any help out there?
Thanks
Lothar
RTTI in C++ is not sophisticated enough to get you a static function if
you have a typeid or another "runtime id" of the event class.
You could probably construct your own metadata ("Runtime Class") so you
could refer to an instance of "RunTime class" from a virtual method of
your event or from "dispatchEvent" or similar method of your event
dispatcher, based on the result of some virtual method of the event
returning some form of its class id (maybe even typeid).
Alternatively, with somewhat lesser flexibility, you could put your
intercepting logic into the method of the event itself, something along
these lines:
class Event;
class EventHandler {
public:
virtual void handle(Event *)=0;
};
class Event {
public:
void process() {
if (!intercept())
handler_.handle(this);
} // I assume that's what you meant by "adding pointer to the event name"
virtual bool intercept(Event *) = 0;
private:
EventHandler handler_;
};
class ConcreteEvent : public Event {
public:
bool intercept() {
// one algorithm per event class here
// so no need to register
}
};
I am not sure I captured your problem fully; it would help if you posted
some source code to illustrate the issue.
-Pavel