How to access properties of factory instances

Questions
1

Hi there. Firstly, as this is my first post, greetings! Nice to meet you all.

I’ve just started out with a small practice project to get the hang of Defold as I’m working through some tutorials, but I’ve come up against my first problem.

I want to create some moving asteroids on my screen, so I’ve created a factory and I’m writing the factory script. I want each asteroid to have a velocity property so that later on in my update loop I can move each asteroid instance at a different speed. I figured it would also be a good idea to store the id of each factory instance in an array so I can access them later.

Here’s what I’ve got so far:

function init(self)
    self.idArray = {}
    for n = 1, 20 do
        local id = factory.create('/asteroids#factory', position, rotation, {velocity = math.random() * 5}, scale)
       table.insert(self.idArray, id) 
    end
end

Now, in the update function, how do I access the velocity property of each instance? I can get the ID’s from my array, but it seems that to get a property from a game object I need its url rather than just its ID.

This is what I have so far in my update function:

function update(self, dt)
    for n = 1, 20 do
        id = self.idArray[n]

        local velocity = go.get(what goes here? , 'velocity')
    end
end

Many thanks in advance!

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2

There might be a simpler way, but I think this should work as your “what goes here?”:

msg.url(nil, self.idArray[n], "name_of_the_script_attached_to_it")

What you need is the url pointing to the script, rather than just the game object.

More can be found here.

3

Thanks for your response Klear.

When you say ‘name of script attached to it’, do you mean the id of the script I’m currently writing - ie. the script that’s creating the factory instances?

If so, then using your example, I’m writing this:

local url = msg.url(nil, self.idArray[n], "asteroidScript")
local velocity = go.get(url , 'velocity')

I think I understand the principle, but it’s giving me this error, pointing to the second line of the above code:

could not find component 'asteroidScript' when resolving '(null)'

So I’m still confused. What exactly is ‘null’ here?

4

Not sure about the null there, but you need to address it to the script attached to the asteroid that’s spawned by the factory rather than your current script.

5

Hmmm, the asteroid spawned by the factory doesn’t have a script attached to it. Should it have? And what should go in it?

Ah … I think I’m beginning to grasp the idea here, so if I add a prototype script to the prototype asteroid, then I can set the velocity property and update its position there, rather than in the factory script. Yep, that works! Thanks for your help!

6

And here: Factory component manual

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