Cooked up a basic event listener manager

eezing

*My second update. Previous posts were overly complicated and impractical.

Some simple code to add/remove listeners. Nothing special going on here, I basically wanted the ability to remove all listeners pertaining to a specific sprite in one line.

You'll notice in the 'addListener' function, there is a 'target' parameter. This should be used when the event you're listening for is not dispatched to the sprite handling the listener function.

No additional closures are created so performance of a dispatched event is normal.

MySprite = Core.class(Sprite)   function MySprite:addListener(type, listener, data, target)   local store = self.myEventStore or {} local target = target or self   if not store[type] then   store[type] = { listener = listener, data = data, target = target }   target:addEventListener(type, listener, data) end     self.myEventStore = store end   function MySprite:removeListener(type)   local store = self.myEventStore local event = store[type]   if store and event then   event.target:removeEventListener(type, event.listener, event.data)   store[type] = nil   self.myEventStore = store end end   function MySprite:removeAllListeners()   local store = self.myEventStore   if store then   for type, event in pairs(store) do   event.target:removeEventListener(type, event.listener, event.data) end   self.myEventStore = nil end end

Use like so:

------- Make listener --------   -- Make sprite local sprite = MySprite.new()   -- Listener function local function onEvent(sprite, event)   print(event:getType()) end     -------- Example A ----------   -- Add a Listener sprite:addListener("goat", onEvent, sprite)   -- Dispatch Event: Good! sprite:dispatchEvent(Event.new("goat"))     -- Remove Listener sprite:removeListener("goat")   -- Dispatch Event: Nothing! sprite:dispatchEvent(Event.new("goat"))     -------- Example B ------------   -- Add a couple Listeners sprite:addListener("beast", onEvent, sprite) sprite:addListener("cheese", onEvent, sprite)   -- Dispatch those events: Good! sprite:dispatchEvent(Event.new("beast")) sprite:dispatchEvent(Event.new("cheese"))     -- Remove all Listeners sprite:removeAllListeners()   -- Dispatch those events: Nothing! sprite:dispatchEvent(Event.new("beast")) sprite:dispatchEvent(Event.new("cheese"))     ------ Example C ---------------   -- Make another sprite ( note: doesn't have to be MySprtie class ) local otherSprite = Sprite.new()   -- Add a Listener to target otherSprite sprite:addListener("chicken", onEvent, sprite, otherSprite)   -- Dispatch event: good! otherSprite:dispatchEvent(Event.new("chicken"))   -- Remove listener for other sprite sprite:removeListener("chicken")   -- Dispatch event: Nothing! otherSprite:dispatchEvent(Event.new("chicken"))

john26

pretty impressive! I can see being able to remove all listeners is useful. Not so sure why you would need to have listeners that only fire once? The "manually remove" option seems to be identical to the existing functionality of addEventListener.

Of course, I'm sure you know, it is not necessary to remove listeners before removing a sprite. Just remove/nil out the sprite and all its listeners die with it. (unless I'm completely wrong...)

eezing

@ john26

You're reply got me wondering, so I did some testing and here's what I came up with...

Yes, if a sprite doesn't exist, then events attached to it will die... but only upon garbage collection. From my experience, garbage collection by default doesn't happen too frequently in cases where memory consumption is low.

Now... a sprite that doesn't exist means that:

- It can't be a parent
- It can't be a child
- it can't be referenced in a living table or variable

Here's a sample of what would be required to remove an event listener without manually doing so:

-- Make Sprite & reference elsewhere --------------------------------   local sprite = Sprite.new() stage:addChild(sprite)   local someTable = {[1] = sprite}   -- Sprite is now a child of stage and -- is referenced in some table       -- Event Listener --------------------------------   -- A local on frame function local function onFrame(self)   print(os.clock()) end   -- Add on frame event listener sprite:addEventListener(Event.ENTER_FRAME, onFrame, sprite)       -- Destroy sprite so event listener will go away automatically -------------------------------   -- First, remove table reference someTable[1] = nil   -- Second, remove from parent (stage) sprite:removeFromParent()   -- Third, nil out sprite sprite = nil   -- Fourth, garbage collect! collectgarbage("collect")     -- Note: If any of the four steps above is -- not done, listener will live on.

john26

I see your point now. Indeed, I think Gideros dispatches ENTER_FRAME events to all sprites even those not on the display tree. So even if you remove a sprite it may still get and act on events. So you need to kill the event listener. However, I think this does not apply to touch events (i.e. touch events are only dispatched to sprites on the display tree). I've never quite understood why it was designed in this way as it means (if I understood correctly) that sprites that are waiting for garbage collection can still do things which is a bit weird...

BTW, Longford does not pass any events to sprites which have been removed from the display tree.

http://www.giderosmobile.com/forum/discussion/4469/introducing-longford-a-partly-gideros-compatible-open-source-game-engine

eezing

@john26

Thanks for posting that link. That engine you have there has a lot of nice features. I need to check it out further.

Btw, can longford export to windows 8 app (windows store)?

john26

Well, it can export a stand-alone windows executable which will run on Intel Windows (will not run on Win RT or Windows Phone 8). Basically its written using standard Win32 API which goes back many years and is still supported (at least in the Desktop mode). However, to get the app in the actual Windows Store may need to add some "Metro style" APIs. But since Longford is open source it's possible to add all these things. If you are knowledgeable about Windows 8 (and Win Phone 8) perhaps you could help to do the port? That's the beauty of having an open source project. And Longford should be very portable, most source code files are completely OS agnostic.