Custom Broadcast Events

moopf · October 2012

I've seen this mentioned before and found a thread from last December about it (here: http://www.giderosmobile.com/forum/discussion/287/suggestion-for-custom-events#Item_1 ) but are custom broadcast events possible yet? By that I mean an event that goes to all objects that have a listener for it, rather than just a specific object?

I think I've got a way around it by getting my sub-objects to register a listener on the main parent that receives the event. I've done this by something like the following in the constructor for my objects:

<pre>
function Blah:init()
	function stageAdded(event)
		gamespace:addEventListener("game_paused", pauseGame) 
		gamespace:addEventListener("game_resumed", resumeGame) 
	end
 
	function stageRemoved(event)
		gamespace:removeEventListener("game_paused", pauseGame)
		gamespace:removeEventListener("game_resumed", resumeGame)
	end
 
	self:addEventListener(Event.ADDED_TO_STAGE, stageAdded) 
	self:addEventListener(Event.REMOVED_FROM_STAGE, stageRemoved) 
end

This appears to work (although I haven't tested it fully) but it's a bit of a hack really because gamespace (in this example) is global.

Mells · October 2012

Hi @moopf,

I don't have much time to answer but there were a couple of suggestions that people made on that thread :
Broadcast messages for custom events : how to?.

That's the result I got : Broadcast messages - result

I hope you will find some things that will help you there.

moopf · October 2012

Hi @Mells, thank for that. I did see your thread as well about messages but I'm looking for something where the receivers are more arbitrary, and trying to avoid lots of loops to achieve it.

I think there's a problem with my solution though as I'm getting periodic crashes caused by the event dispatcher dispatching an event to an object that's no longer a child. Going to debug that this morning to see what's going on. As I'm removing all children from the scene before destroying them, first place to check is that Event.REMOVED_FROM_STAGE is actually triggering 100% of the time.

atilim · October 2012

Using weak tables can be another option:

allEventDispatchers = setmetatable({}, {__mode = "v"})
 
function broadcastEvent(event)
	for k in pairs(allEventDispatchers) do
		k:dispatchEvent(event)
	end
end
 
-- usage example
 
MySprite = Core.class(Sprite)
 
function MySprite:init()
	allEventDispatchers[self] = true
	-- init continues from here
	self:addEventListener("foo", function() print("foo") end)
end
 
MySprite = MySprite.new()
 
broadcastEvent(Event.new("foo"))

moopf · October 2012

Hi @atilim, that's a really good idea actually. I think I'll take your idea here and change my code this morning as this should automatically resolve calls to objects that no longer exist which is apparently what I'm currently getting with my quick and dirty solution at the moment

Mells · October 2012

@atilim
I learned something new today.

For those who want to have a better understanding of the solution provided by atilim :
Weak Tables Tutorial - at lua-users.org

moopf · October 2012

@Mells Weak tables are very useful, I just hadn't thought of using it in this situation but it's a good solution to the problem.

atilim · October 2012

Also after reading your post, I've decided to test Event.ADDED_TO_STAGE and Event.REMOVED_FROM_STAGE again and couldn't catch any bugs. For the people who are interested, here is my test code:

local spritesOnStage = {}
 
MySprite = Core.class(Sprite)
 
function MySprite:init()
	self:addEventListener(Event.ADDED_TO_STAGE, self.onAddedToStage, self)
	self:addEventListener(Event.REMOVED_FROM_STAGE, self.onRemovedFromStage, self)
end
 
function MySprite:onAddedToStage()
	if spritesOnStage[self] == true then
		print("error! onAddedToStage")
	end
	spritesOnStage[self] = true
end
 
function MySprite:onRemovedFromStage()
	if spritesOnStage[self] == nil then
		print("error! onRemovedFromStage")
	end
	spritesOnStage[self] = nil
end
 
local function populate(sprite, sprites)
	for i=1,sprite:getNumChildren() do
		local child = sprite:getChildAt(i)
		sprites[child] = true
		populate(child, sprites)
	end
	return sprites
end
 
local function check()
	local spritesOnStage2 = populate(stage, {})
 
	for k,v in pairs(spritesOnStage) do
		if spritesOnStage2[k] == nil then
			print("error! check1")
		end
	end
 
	for k,v in pairs(spritesOnStage2) do
		if spritesOnStage[k] == nil then
			print("error! check2")
		end
	end
end
 
local sprites = {}
for i=1,20 do
	sprites[i] = MySprite.new()
	stage:addChild(sprites[i])
end
sprites[#sprites + 1] = stage
 
local n = 0
 
local function onEnterFrame()
	if math.random(1, 4) == 1 then
		local sprite = sprites[math.random(1, #sprites - 1)]
		sprite:removeFromParent()
	else
		local sprite1 = sprites[math.random(1, #sprites)]       
		local sprite2 = sprites[math.random(1, #sprites - 1)]       
		pcall(function() sprite1:addChild(sprite2) end)
	end
	check()
	n = n + 1
	if n % 100 == 0 then
		print("tested "..n.." tree mutations...")
	end
end
 
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)

moopf · October 2012

Hi @atilim, yes it was my own stupidity causing the crash. Took me a while to track down what was going on but got there in the end (it was unrelated to by ADDED_TO_STAGE, REMOVED_FROM_STAGE listeners but I've changed that implementation to yours which is definitely better). It was all to do with registering on the wrong object rather than self.

atilim · October 2012

@moopf, when somebody mentions a possibility of a bug, I can't wait to test it

moopf · October 2012

haha, yes I know that feeling all too well @atilim - that's why I won't call something a bug here unless I'm pretty sure it is. I hate investigating something that isn't actually broken even though sometimes it can be a useful exercise.

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