Back to General and Gameplay Programming

[C++] Looking for feedback on my event system

Shadeirou · 2011-09-26T11:24:45

I've been trying to decide how to format my event messaging system for a while now, but could never settle on a way to do it. My goals for this system were to make it fast, intuitive, and easily expandable (meaning I can easily add listeners for whatever event type I want). I ended up settling on the observer pattern to handle the way in which objects get informed of an event because it seems fast, but more so because it conforms to the design pattern of the rest of my engine. So here is what I have. To me, it still seems like a strange way of doing it, as it seems template heavy, but it has performed well in my tests and is pretty easy to use. I would appreciate any suggestions, criticisms, improvements, other designs, etc. Event classes: // Description: All events derive from this base class. This can be used to // store events of different types together. // // Inheritance: None // // Example Usage: // std::vector<EventBase*> events; // events.push_back(new KeyDownEvent()); // events.push_back(new KeyUpEvent()); class EventBase { public: // ctors/dtor: ============================================================= EventBase() : handled_(false) {} virtual ~EventBase() {} // public functions: ======================================================= void SetHandled(bool handled) { handled_ = handled; } bool IsHandled() const { return handled_; } protected: // protected static functions: ============================================= static unsigned int GenerateUniqueID(); private: // vars: =================================================================== bool handled_; }; unsigned int EventBase::GenerateUniqueID() { static unsigned int id = 0; ++id; return id; } // Description: Generates a unique integer ID for an event that derives from // this class. All concrete events should derive from this class. // // Inheritance: EventBase -> Event<EventT> // // Example Usage: // class SomeEvent : public Event<SomeEvent> { // public: // SomeEvent(int data) : data_(data) {} // // void SetData(int data) { data_ = data; } // int GetData() const { return data_; } // // private: // int data_; // }; template<typename EventT> class Event : public EventBase { public: // public static constants: ================================================ static const unsigned int kID; }; template<typename EventT> const unsigned int Event<EventT>::kID = Event<EventT>::GenerateUniqueID(); Listener classes: // Description: All event listeners derive from this base class. This can be // used to store listeners of different types together. // // Inheritance: None // // Example Usage: // std::vector<EventListenerBase_Interface*> listeners; // listeners.push_back(new KeyDownListener()); // listeners.push_back(new KeyUpListener()); class EventListenerBase_Interface { public: // ctors/dtor: ============================================================= virtual ~EventListenerBase_Interface() {} }; // Description: Generates a unique OnEvent method for each event input for // EventT. All event listeners should derived from this class. // // Inheritance: EventListenerBase_Interface -> EventListener_Interface<EventT> // // Example Usage: // class SomeEventListener // : public EventListener_Interface<KeyDownEvent>, // public EventListener_Interface<KeyUpEvent> { // public: // SomeEventListener() {} // // void OnEvent(KeyDownEvent* event) { // // do something // } // // void OnEvent(KeyUpEvent* event) { // // do something // } // }; template<typename EventT> class EventListener_Interface : public EventListenerBase_Interface { public: // dtors: ================================================================== virtual ~EventListener_Interface() {} // public functions: ======================================================= virtual void OnEvent(EventT* event) = 0; }; EventDispatcher: // Description: Used to register events listeners and dispatch events. // // Inheritance: None // // Example Usage: // EventDispatcher dispatcher; // SomeListener listener; // // dispatcher.Register<SomeEvent>(SomeEvent::kID, &listener); // dispatcher.Dispatch(SomeEvent::kID, new SomeEvent()); class EventDispatcher { public: // typedefs: =============================================================== typedef std::vector<EventListenerBase_Interface*> ListenerVector; typedef std::map<int, ListenerVector> ListenerMap; // ctors/dtor: ============================================================= EventDispatcher() {} // public functions: ======================================================= // - dispatch event template<typename EventT> void Dispatch(int type, EventT* event); // - register listeners template<typename EventT> void Register(int type, EventListener_Interface<EventT>* listener); private: // vars: =================================================================== ListenerMap listeners_; }; template<typename EventT> void EventDispatcher::Dispatch(int type, EventT* event) { if (event == NULL) { return; } // disallow a NULL event ListenerMap::iterator itr = listeners_.find(type); if (itr == listeners_.end()) { return; } // event type not found // dispatch event to the listeners for (unsigned int x = 0; x < itr->second.size(); ++x) { static_cast<EventListener_Interface<EventT>*>( itr->second.at(x))->OnEvent(event); } } template<typename EventT> void EventDispatcher::Register(int type, EventListener_Interface<EventT>* listener) { if (listener == NULL) { return; } // disallow a NULL listener listeners_[type].push_back(listener); } Again, feedback would be greatly appreciated. I would prefer not to use RTTI, but I'm open to suggests. Thanks. EDIT: De-virtualized SetHandled and IsHandled in EventBase and removed the ctor and dtor for Event at Ftn's suggestion. EDIT: Altered Register in EventDispatcher in the way __sprite suggested.

General and Gameplay Programming Programming

Started by Shadeirou September 07, 2011 02:32 AM

44 comments, last by _the_phantom_ 12 years, 6 months ago

Zipster

2,420

September 19, 2011 06:46 PM

You could always create a wrapper object that allows you do uniquely identify the callbacks:



struct EventCallback

{

   int id;

   std::function callback;

};

However then you'd probably use a handle pattern, where the dispatcher allocates a unique ID that gets returned on registration, and the user holds on to that ID and uses it later for unregistration.Not necessarily ideal, but it does work without adding too much complexity to the implementation.

popsoftheyear

2,195

September 19, 2011 07:04 PM

I'm now switched over to a design very similar to the one posted by phantom, with my own modifications here and there, but have run into a problem: unregistering listeners. Before it was as simple as iterating through a vector of listeners and removing the object that was the same as the one passed into the function. Now that is not possible because std::functions aren't comparable. I've a few ideas on how to solve this, but they add some annoying layer of complexity that I really don't want. Any ideas?

http://www.codeproject.com/KB/cpp/FastDelegate.aspx

Those are comparable if that's of any help... I've always had great success with them.

Shadeirou

105

Author

September 20, 2011 06:48 AM

[font="arial, verdana, tahoma, sans-serif"] [/font]
[font="arial, verdana, tahoma, sans-serif"]You could always create a wrapper object that allows you do uniquely identify the callbacks:[/font]
[font=arial, verdana, tahoma, sans-serif]
[/font] [font=arial, verdana, tahoma, sans-serif]struct EventCallback[/font] [font=arial, verdana, tahoma, sans-serif] {[/font] int id; std::function callback; };

However then you'd probably use a handle pattern, where the dispatcher allocates a unique ID that gets returned on registration, and the user holds on to that ID and uses it later for unregistration.Not necessarily ideal, but it does work without adding too much complexity to the implementation.

Yeah, I thought of something similar and it is definitely not ideal. I think this is where the observer pattern using interfaces has the upper hand; It's nice to be able to just pass the object in to unregister.

http://www.codeproje...stDelegate.aspx

Those are comparable if that's of any help... I've always had great success with them.

I've seen this, but only because I saw this first and it is a response to that. I would probably use the "Impossibly Fast Delegates" if I were going to forgo std::function.

popsoftheyear

2,195

September 20, 2011 02:14 PM

Well, those aren't comparable

You may be surprised how well it works!

Shadeirou

105

Author

September 26, 2011 09:30 AM

Thanks for all the input everyone. I think my event system is at a good place now. It is integrating smoothly into my applications. This is a result of messing around with my currently implemented event system.

_the_phantom_

11,263

September 26, 2011 11:24 AM

No worries; was an intresting discussion and gave me some stuff to think about/test with regards to my own Awesome Plans™ in this area

Intresting sidenote; I was watching a recent //Build presentation on C++ and WinRT and it seems that MS have come up with the same 'solution' as I did when it comes to binding events in C++. When they add a C++ delegate to an WinRT event you get given back a token and you use that token to unregister your delegate later. Much the same as I proposed both here and the other thread on Event systems

[C++] Looking for feedback on my event system

`[/font] [font=arial, verdana, tahoma, sans-serif]struct EventCallback[/font] [font=arial, verdana, tahoma, sans-serif] {[/font] int id; std::function callback; };`

struct EventCallback[/font]
[font=arial, verdana, tahoma, sans-serif]

{[/font]
int id;
std::function callback;
};

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

[C++] Looking for feedback on my event system

[/font] [font=arial, verdana, tahoma, sans-serif]struct EventCallback[/font] [font=arial, verdana, tahoma, sans-serif]{[/font] int id; std::function callback; };

struct EventCallback[/font] [font=arial, verdana, tahoma, sans-serif]

{[/font] int id; std::function callback; };

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines

`[/font] [font=arial, verdana, tahoma, sans-serif]struct EventCallback[/font] [font=arial, verdana, tahoma, sans-serif] {[/font] int id; std::function callback; };`

struct EventCallback[/font]
[font=arial, verdana, tahoma, sans-serif]

{[/font]
int id;
std::function callback;
};