Closure Help Needed

Solar2D Lua Language
#1

I’m attempting to use Lua’s closures in the following bit of code:

[lua]

for k,v in pairs(tiles) do
            for key, value in pairs(v) do
                position.xPos = value[1]
                position.yPos = value[2]
               
                if self.inventoryData[itemId].Type == “Seed” then
                    item = SeedClass.new(itemData, self._game, position) –
                    self.items[item.id] = item
                   
                    TaskManager:addTask({id=item.id, desc="Plant “…item.name, duration=15000, repeated=false,
                    callback = function()
                        print(”* x: “…item.mainImage.x) --always referring to last item created in the for loop
                        print(”* Y: "…item.mainImage.y) --always referring to last item created in the for loop
                        return item:action({x=item.mainImage.x, y=item.mainImage.y}) --always referring to last item created in the for loop
                    end})
                end
            end
        end

[/lua]

Many thanks…

The idea being that a task is added to create the object, once the task’s duration has passed the object is displayed on screen in the item:action() call via a call to the task.callback() method.

Although this code works fine it comes across a problem when I’m trying to spawn multiple objects; the callback function only refers to the last item created up above - so the call to item:action is always being made on the last created item object. I’m pretty sure there’s a way to do this via the corretc use of closures, but can’t seem to get it right yet…

Any 

#2

OK… so no sooner do I post then I find a solution…

[lua]

item = SeedClass.new(itemData, self._game, position) –
                    self.items[item.id] = item
                   
                    local function createTask(item)
                        return TaskManager:addTask({id=item.id, desc="Plant “…item.name, duration=15000, repeated=false,
                        callback = function()
                            print(”* x: “…item.mainImage.x)
                            print(”* Y: "…item.mainImage.y)
                            item:action({x=item.mainImage.x, y=item.mainImage.y})
                        end})
                    end
                   
                    createTask(item)

[/lua]

I’ve changed the code to this, it gets around the problem of ensuring the correct instance data is passed - however it’s far from an elegant solution, so be interested to know whether anybody has any better alternatives.

Many thanks…

#3

You did not post where you call the callback function and where is the callback variable declared it looks like it’s global thus will change for ever new instance.

#4

Hi Primoz…

The callback function is called in the TaskManager class.  Essentially there is a method in that class that calls the callback when the task duration is finished:

[lua]

function TaskManager:isTaskReady(id)
    if self.mTasks[id].taskDuration <= 0 then
        self.mTasks[id].callback()
        if self.mTasks[id].repeated == false then
            self:removeTask(id)
        end
        return true
    end
end

[/lua]

The callback variable is part of a table that is passed through in the code above to TaskManager:addTask(), as so:

[lua]

TaskManager:addTask({id=item.id, desc="Plant "…item.name, duration=15000, repeated=false,

callback = function()

  print("* x: “…item.mainImage.x) --always referring to last item created in the for loop
  print(”* Y: "…item.mainImage.y) --always referring to last item created in the for loop
  return item:action({x=item.mainImage.x, y=item.mainImage.y}) --always referring to last item created in the for loop

end})

[/lua]

The technique in my second post works, I just thought there might be a more elegant solution then encapsulating the call within a function.

Thanks for checking over it for me…

#5

Ah sorry I missed that it was a parameter.

What I like to do in a case like this is to add just the reference to the function that needs to be called and a table of parameters that it needs like so:

params = { 1, “something” }

task = {call = func1, params = params }

TaskManager.addTask(task)

and when task manager calls it just do this:

task.call(unpack(task.params))

#6

OK… so no sooner do I post then I find a solution…

[lua]

item = SeedClass.new(itemData, self._game, position) –
                    self.items[item.id] = item
                   
                    local function createTask(item)
                        return TaskManager:addTask({id=item.id, desc="Plant “…item.name, duration=15000, repeated=false,
                        callback = function()
                            print(”* x: “…item.mainImage.x)
                            print(”* Y: "…item.mainImage.y)
                            item:action({x=item.mainImage.x, y=item.mainImage.y})
                        end})
                    end
                   
                    createTask(item)

[/lua]

I’ve changed the code to this, it gets around the problem of ensuring the correct instance data is passed - however it’s far from an elegant solution, so be interested to know whether anybody has any better alternatives.

Many thanks…

#7

You did not post where you call the callback function and where is the callback variable declared it looks like it’s global thus will change for ever new instance.

#8

Hi Primoz…

The callback function is called in the TaskManager class.  Essentially there is a method in that class that calls the callback when the task duration is finished:

[lua]

function TaskManager:isTaskReady(id)
    if self.mTasks[id].taskDuration <= 0 then
        self.mTasks[id].callback()
        if self.mTasks[id].repeated == false then
            self:removeTask(id)
        end
        return true
    end
end

[/lua]

The callback variable is part of a table that is passed through in the code above to TaskManager:addTask(), as so:

[lua]

TaskManager:addTask({id=item.id, desc="Plant "…item.name, duration=15000, repeated=false,

callback = function()

  print("* x: “…item.mainImage.x) --always referring to last item created in the for loop
  print(”* Y: "…item.mainImage.y) --always referring to last item created in the for loop
  return item:action({x=item.mainImage.x, y=item.mainImage.y}) --always referring to last item created in the for loop

end})

[/lua]

The technique in my second post works, I just thought there might be a more elegant solution then encapsulating the call within a function.

Thanks for checking over it for me…

#9

Ah sorry I missed that it was a parameter.

What I like to do in a case like this is to add just the reference to the function that needs to be called and a table of parameters that it needs like so:

params = { 1, “something” }

task = {call = func1, params = params }

TaskManager.addTask(task)

and when task manager calls it just do this:

task.call(unpack(task.params))