Accessing children from parent class

ar2rsawseen

Is this a bug, or this wasn't meant to be used this way? Basically I create my own class derived from Sprite and inside constructor I add eventlistener to mouse down, to iterate through all children of this custom sprite.
Then I extend this custom class, and add method for adding children. And when I start it and click it, it simply dies without any error message

Here's an example code:

MyClass = Core.class(Sprite)   function MyClass:init() self:addEventListener(Event.MOUSE_DOWN, self.handler, self) end   function MyClass:handler() local children = self:getNumChildren() for i = 1, children do local sprite = self:getChildAt(i) print(sprite) end end   MyExtendedClass = Core.class(MyClass)   function MyExtendedClass:add(elem) self:addChild(elem) end   local container = MyExtendedClass.new() stage:addChild(container) container:add(Bitmap.new(Texture.new("crate.png"))) container:add(Bitmap.new(Texture.new("crate.png"))) container:add(Bitmap.new(Texture.new("crate.png"))) container:add(Bitmap.new(Texture.new("crate.png")))

If I do the same for each extended class it works great, problem is only if I iterate in parent class. It retrieves getNumChildren() correclty but dies on local sprite = self:getChildAt(i)

If it's not meant to be used this way, is there any other way I can reuse my code, so I won't have to write the same functions on all extended classes?

Nascode

@ar2rsawseen i tried your code, and it really crashed the simulator or the iphone gideros player. Is it a bug?

zvardin

When I click, the handler fires twice as well. I wonder if this might be related to how the parent class is stored.

zvardin

It still crashes when I do this, but if I add a blank declaration for MyExtendedClass:init the event handler only fires once.

ar2rsawseen

hmm, that's interesting, so there is a purpose for constructors.

But let's wait and see what @atilim has to say. I'm not saying it is a bug, maybe it was not suppose to work that way, I just want to know if it so, I would simply stop wasting my time and look for other solution
Like static methods and retrieving event target, or something similar

atilim

ohhh... lovely bug

This is because of there are two different selfs when you inherit multiple times. @ar2rsawseen, most probably you remember this thread: http://www.giderosmobile.com/forum/discussion/834/possible-bug-self-in-base-class-init-function-is-not-equal-to-self-in-the-derived-class-init

The exact solution is dropping the deep copying and always make sure that there is always one self. And in your specific example, the solution is moving the line

self:addEventListener(Event.MOUSE_DOWN, self.handler, self)

to MyExtendedClass's constructor. So that you register the event with the correct self.

@ndoss said that two different selfs can cause subtle & difficult to find problems and this is a great example of it.

Similar to your example, this code also crashes exactly with the same reason:

local sprite = Sprite.new()   sprite:addChild(Sprite.new()) sprite:addChild(Sprite.new()) sprite:addChild(Sprite.new()) sprite:addChild(Sprite.new())   sprite.__children = nil -- mess with internal data   sprite:getChildAt(1)

This is not a bug because I always assume that users don't mess with internal data therefore I don't check consistency to be more efficient.

thank you

ar2rsawseen

I knew I've read somewhere about it. Just could not remember.
Ok thanks, moving addEventListener helps and everything works as expected

joelghill

Wait.... we can inherit from custom classes that we create? Or extend them? I thought I read that didn't work. I guess I'll have to try something like that.

Mells

@atilim what is the future for this : "there are two different selfs when you inherit multiple times"?

Let me change deep copy to shallow copy and test extensively.
(And honestly I don't remember why I preferred deep copy instead of shallow )

Any updates, or is the solution that you suggested the definitive one to remember, use now and in the future?

ndoss

Wait.... we can inherit from custom classes that we create? Or extend them? I thought I read that didn't work. I guess I'll have to try something like that.

Yes, you can inherit from your own classes. Wasn't always that way...you probably read older documentation

joelghill

@ndoss Oh that's awesome, I'm glad that was added!

atilim

yay! I'm back..

here is the old Core.class function:

Core.class = function(b) local c = {} c.__index = c setmetatable(c, b)   if b == nil then c.new = function(...) local s1 = {}   setmetatable(s1, c)   if s1.init ~= nil and type(s1.init) == "function" then s1:init(...) end   return s1 end else c.new = function(...) local b = getmetatable(c)   local s0 = b.new(...) local s1 = {}   for k,v in pairs(s0) do s1[k] = v end   setmetatable(s1, c)   if s1.init ~= nil and type(s1.init) == "function" then s1:init(...) end   return s1 end end   return c end

and here is the new one:

Core.class = function (b) local c = {} c.__index = c setmetatable(c, b)   if b == nil then c.new = function(...) local s1 = {}   setmetatable(s1, c)   local init = rawget(c, "init") if type(init) == "function" then init(s1, ...) end   return s1 end else c.new = function(...) local b = getmetatable(c)   local s1 = b.new(...)   setmetatable(s1, c)   local init = rawget(c, "init") if type(init) == "function" then init(s1, ...) end   return s1 end end   return c end

@Mells if you want, you can create an init.lua file and copy the new Core.class function into it to override the old one.

techdojo

@Atilim - will this fix be in the next update?

gorkem

@techdojo fixed due next release