How to add a Listener that is a static class function

beginners
#1

Every time update events happen I want to callback a static class function. Any ideas on how to do this. ofAddListener seems to want to take a pointer to an object. But I dont have one? I tried passing NULL as the pointer but it did not work.

#2

right now i’m creating a new class just for update listening. Them making an instance from that class, which is a static class member. Anyone know a better way?

#3

openFrameworks doesn’t provide directly a way of making a static function or a non member function a listener but you can use Poco syntax (the library in which OF events are based):

ofEvents().update += Poco::priorityDelegate(&updateFunction,OF_EVENT_ORDER_APP);

where updateFunction, is a static or c function with signature:

void updateFunction(ofEventArgs & args)
#4

Thanks Arturo!

#5

does using -= remove listeners? How do I remove listeners?

#6

yeah, just use the same syntax with -=

#7

I have a problem when I do something like

ofEvents().update += Poco::priorityDelegate(&updateFunction,OF_EVENT_ORDER_APP);
ofEvents().update += Poco::priorityDelegate(&updateFunction,OF_EVENT_ORDER_APP);

It seems to be adding the listener twice? Is there any way check whether the function has been added already?

#8

no but you can just remove it before adding it, remove will just do nothing if it wasn’t added before

#9

cool trick thanks!