stuck with simple custom event

jalmince · January 2014

Hi there! Hope somebody can help, or explain.

I stripped down my code to the basic following and still can' t understand what is wrong:

object 1 ( class Gun) sends a custom event ("shoot"), object 2 ( class target ) never gets it ( at least the way I am coding it..)

---------------------( gun.lua ) -------
Gun = gideros.class(Sprite)

function Gun:init()
print( "gun created" )
function Gun:onMouseDown()
self:dispatchEvent(Event.new("shoot"), self)
print( " shoot dispatched ")
end
self:addEventListener( Event.MOUSE_DOWN, self.onMouseDown, self)
end

-------------------------( target.lua )------------
Target = gideros.class(Sprite)

function Target:init()
self:addEventListener( "shoot", function() print("got it") end)
print( " Target created, listening to shoots")
end

-------------------(main.lua) -------------
target = Target.new()
gun = Gun.new()

stage:addChild( gun)
stage:addChild( target)
--------------------------------------

In the output window, I get:

Uploading finished.
Target created, listening to shoots
Gun created
shoot dispatched
shoot dispatched
shoot dispatched
....
but never see "got it" from the event listener ??

thanks in advance if somebody can sort me out !

JP

OZApps · January 2014

@jalmince, could it be that you have the listener on Target but are dispatching the events to Gun, so Target never receives the events.

ar2rsawseen · January 2014

@jalmince yes the objects need to have something in common, for example the scene they are on

Gun = Core.class(Sprite)
 
function Gun:init(scene) 
	print( "gun created" )
	scene:dispatchEvent(Event.new("shoot"), self) 
end
 
Target = Core.class(Sprite)
 
function Target:init(scene)
	scene:addEventListener( "shoot", function() print("got it") end)
	print( " Target created, listening to shoots")
end
 
Scene = Core.class(Sprite)
 
function Scene:init()
	target = Target.new(self)
	gun = Gun.new(self)
 
	self:addChild(gun)
	self:addChild(target)
end
 
stage:addChild(Scene.new())

oor you can always hack your way out of it, like this:

allEventListeners = setmetatable({}, {__mode = "v"})
 
function broadcastEvent(event)
	for k in pairs(allEventListeners) do
		k:dispatchEvent(event)
	end
end
 
 
Gun = Core.class(Sprite)
 
function Gun:init() 
	print( "gun created" )
	broadcastEvent(Event.new("shoot")) 
end
 
Target = Core.class(Sprite)
 
function Target:init()
	allEventListeners[self] = true
	self:addEventListener( "shoot", function() print("got it") end)
	print( " Target created, listening to shoots")
end
 
 
target = Target.new()
gun = Gun.new()

jalmince · January 2014

@ar2rsawseen : many thanks. Think I get your point: when an object 1 wants to send an event to an object2, the event has to be dispatched to higher up in the hierarchy containing object2 right ?

Many thanks again for your efficiency !!

OZApps · January 2014

@jalmince,

---------------------( gun.lua ) -------
Gun = gideros.class(Sprite)
 
function Gun:init()
  print( "gun created" )
 
  function Gun:onMouseDown()
    self:dispatchEvent(Event.new("shoot"), self)
    print( " shoot dispatched ")
  end
 
  self:addEventListener( Event.MOUSE_DOWN, self.onMouseDown, self)
end
 
-------------------------( target.lua )------------
Target = gideros.class(Sprite)
 
function Target:init()
  self:addEventListener( "shoot", function() print("got it") end)
  print( " Target created, listening to shoots")
end

If you are looking for a detailed understanding, then look at the

gun.lua

the function

Gun:init

works as follows

first it prints the sentence "gun created"

then the function

Gun:onMouseDown()

dispatches an event called shoot and prints "shoot dispatched". This is where you need to look carefully. Dispatch is used as

self:dispatchEvent(Event.new("shoot"), self)

The self in this function is the same as Gun, so essentially what you are using is,

Gun:dispatchEvent(Event.new("shoot"), Gun)

therefore the event is send to the Gun object where as you are expecting the same to be captured by another object.

Now with the Target object, when it is created, it sets the event listener to listen for the custom event "shoot"

What happens as I suggested earlier is that Target never gets the event shoot as the custom event shoot is dispatched to the Gun object not Target.

You can as suggested by @ar2sawseen have a common object that captures and dispatches custom events. One way would be to use the stage object or the Scene as suggested by @ar2rsawseen.

jalmince · January 2014

Many thanks, I got it now ..
by the way how do you post nicely formatted and syntax colored text ?
thanks again,
Jp

ar2rsawseen · January 2014

http://members.giderosmobile.com/knowledgebase.php?action=displayarticle&id=41

Howdy, Stranger!

Categories

In this Discussion

Top Posters

stuck with simple custom event

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

stuck with simple custom event

Comments