ofxAddons
Bringing te power of lambda to ofEvent
README
ofxLambdaEvent
Bringing te power of lambda to ofEventCredits
The core lambda logic is handled by the internal ``ofxLiquidEvent` class, which is grabbed directly from https://github.com/elliotwoods/ofxLiquidEvent so all those credits go to elliotwoods (I just added the locking and modification queueing). The reason I copied his class instead of using his addon, is to keep the dependency list clean, and adding another addon dependency for a single file seems like an unnecessary pain in the ass.
Explanation
This addon provides a `LambdaEvent` class which is basically nothing more than ofEvent and ofxLiquidEvent merged into one, with some logic to tie the two together and some extra convenience methods.
Note also that the `LambdaEvent` class has no smart logic to trigger the listeners in the proper order when both ofEvent-style listeners and ofxLiquidEvent-style lambdas are used. Mixing both types on the same event is possible but simply not recommended; use your preferred method consistently.
Usage - lambda only
_You can use a LambdaEvent like an ofxLiquidEvent_
`c++ // create an event instance LambdaEvent<SomeCustomObjectType> customEvent; // register a listener; // arg1 is the lambda that will be called when the event is triggered // arg2 (this) is linked to the lambda so you can later unregister the lambda customEvent.addListener([](SomeCustomObjectType obj){ doSomethingWith(obj); }, this); // trigger the event customEvent.notifyListeners(instanceOfSomeCustomObjectType); // unregister lambda; this will remove ALL lambdas which were registered with 'this' as second argument customEvent.removeListeners(this);
Usage - like an ofEvent
_You can use LambdaEvent like an ofEvent_
c++ // create an event instance LambdaEvent<SomeCustomObjectType> customEvent; // register listener, like you would do with ofEvent ofAddListener(customEvent, this, &ThisClass::listenerMethod); // trigger event ofNotifyListeners(customEvent, instanceOfSomeCustomObjectType); // unregister listener ofRemoveListener(customEvent, this, &ThisClass::listenerMethod);
Usage - using lambdas on an existing ofEvent
If you're using 3rd-party libraries (of core-openFrameworks events) you might have to deal with an existing ofEvent. The
LambdaEvent` class has a convenience method forward that provides an easy work-around to "add lambda support" to an existing ofEvent;
`c++ // create your own LambdaEvent with the same template-type as the existing ofEvent LambdaEvent<ofKeyEventArgs> lambdafierEvent; // let your lambda event "forward" all notifications from the original event lambdafierEvent.forward(ofEvents().keyPressed); // register your own lambda like on the LambdaEvent lambdafierEvent.addListener([](ofKeyEventArgs args){ ofLog() << "I'm never using ofAddListener again!"; }, this);
Note that, obviously, LambdaEvent's destructor cleans up after itself nicely, so it will stop forwarding when de-allocated. If for some reason you want to disconnect from the original ofEvent before that, this is also possible:
lambdafierEvent.stopForward(ofEvents().keyPressed);
Extra - Middleware
The Middleware class has exactly the same API as ofxLiquidEvent (.addListener, .notifyListeners, .removeListeners), but takes lambdas that return a boolean value. If any of the listeners returns false, the notifications immediately end and remaining listeners are not invoked. The notifyListeners function also returns wether all lambdas returned true or not; this way the Middleware class can be used to have listeners inform the notifier about wether to perform a certain process or not.
c++ Middleware<string> uploadMiddleware;
uploadMiddleware.addListener([](string& url) -> bool { return url.substring(0, 8) == "https://"; )}, this);
if(uploadMiddleware.notifyListeners(uploadUrlString)){ // perform upload logic } ``