OOP Question - Passing an object method as a function parameter?

Solar2D Lua Language
#1

I’m trying to pass an object method as a parameter, essentially as a callback function for a network request in another class.

[lua]

function ItemManager:loadData()
    --print(tostring(self:getItemData))

    --cant pass with the : sytax
    Parse.getItems(self.getItemData)
end

[/lua]

This in turn should call the following function/method when the network request is finished.

[lua]

function ItemManager:getItemData(data)
    print("ItemManager: data - "…data.response)
    self.data = data.response
end

[/lua]

The problem is that I can’t pass the function as a method with the : syntax, and if I attempt to pass it with a .  it doesn’t fire the call.

I need getItemData to be a method because it needs to access the object’s properties.

Does anybody know how to handle this situation; or perhaps an alternative way of dealing with this?

Many thanks…

#2

Solution is simple, just wrap your function using colon with anonymous function. Then call this wrapper function which will execute your code.

#3

Thanks for your input, however I still can’t get this to work. I changed it to an anonymous function, like so:

[lua]

function ItemManager:loadData()
    --print(tostring(self:getItemData))
    Parse.getItems(
    function()
        self:getItemData()
    end)
end

[/lua]

However it’s not firing. The only way I’ve managed to get the callback to work is by having a local function like so:

[lua]

local function getItemData(data)
    print("ItemManager: data - "…data.response)
    self:populateData(data.response) 
end

function ItemManager:loadData()
    --print(tostring(self:getItemData))
    Parse.getItems(getItemData)
end

[/lua]

However I need getItemData to be a method as the call to self:populateData won’t work otherwise?!?

#4

Looking further it seems as the anonymous function is being called immediately, perhaps due to the asynchronous nature of network.request.

#5

You put it in wrong place as I see… it’s hard to say because I dont know what your functions do and cannot see data structure.

#6

ItemManager is a basic class - it’s interacting with Parse.com to download a bunch of objects in a Parse.com class. The only real thing that is happening here is passing a callback to a function that makes a query to Parse.com via a network.request() call.

I’m a little confused by what you mean “… wrong place”; all I’m trying to do is pass a callback that refers to a method of ItemManager; however the anonymous function approach doesn’t work (well it seems to fire immediately with event == nil). The only approach that works so far is to have the callback as the local/private function.

Can I just ask where the anonymous call should go? Many thanks for your help.

#7

But shouldn’t function you pass to Parse take an argument?
In your not-working example you made anonymous function but it never takes argument!

I do not know what structure Parse returns but you never pass data from it to your function.
If so it should be

local function func(dataFromParse) self:getItemData(dataFromParse) end Parse.getItems(func)
#8

Thank you Piotrz - the noob problem was that I hadn’t specified the arguments in the anonymous callback function, once I changed that everything is working as expected.

Many thanks…

#9

Solution is simple, just wrap your function using colon with anonymous function. Then call this wrapper function which will execute your code.

#10

Thanks for your input, however I still can’t get this to work. I changed it to an anonymous function, like so:

[lua]

function ItemManager:loadData()
    --print(tostring(self:getItemData))
    Parse.getItems(
    function()
        self:getItemData()
    end)
end

[/lua]

However it’s not firing. The only way I’ve managed to get the callback to work is by having a local function like so:

[lua]

local function getItemData(data)
    print("ItemManager: data - "…data.response)
    self:populateData(data.response) 
end

function ItemManager:loadData()
    --print(tostring(self:getItemData))
    Parse.getItems(getItemData)
end

[/lua]

However I need getItemData to be a method as the call to self:populateData won’t work otherwise?!?

#11

Looking further it seems as the anonymous function is being called immediately, perhaps due to the asynchronous nature of network.request.

#12

You put it in wrong place as I see… it’s hard to say because I dont know what your functions do and cannot see data structure.

#13

ItemManager is a basic class - it’s interacting with Parse.com to download a bunch of objects in a Parse.com class. The only real thing that is happening here is passing a callback to a function that makes a query to Parse.com via a network.request() call.

I’m a little confused by what you mean “… wrong place”; all I’m trying to do is pass a callback that refers to a method of ItemManager; however the anonymous function approach doesn’t work (well it seems to fire immediately with event == nil). The only approach that works so far is to have the callback as the local/private function.

Can I just ask where the anonymous call should go? Many thanks for your help.

#14

But shouldn’t function you pass to Parse take an argument?
In your not-working example you made anonymous function but it never takes argument!

I do not know what structure Parse returns but you never pass data from it to your function.
If so it should be

local function func(dataFromParse) self:getItemData(dataFromParse) end Parse.getItems(func)
#15

Thank you Piotrz - the noob problem was that I hadn’t specified the arguments in the anonymous callback function, once I changed that everything is working as expected.

Many thanks…