Need to :remove a running timer before setting it again with .new?

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1

Back when I was new to Lua and Playdate I was having some kind of problem with re-using a running timer, having the original callback AND the new one both trigger. I don't recall the exact symptoms anymore.

What I wanted was to re-assign the same timer variable and have the old instance—IF ANY—just be gone: never to complete, never to execute the old callback.

So I ended up with this kind of structure ALL over my code: testing for a timer's existence every time I try to use it, and removing it before re-assigning:

local eventTimer = nil

function setEventTimer()
	if eventTimer ~= nil then 
		eventTimer:remove() -- (NEEDED?)
	end
	
	eventTimer = pd.timer.new(2000, doEvent)
end

Is that extra step really necessary? Or should I be OK (and responsible with RAM) just re-assigning eventTimer = pd.timer.new without removing the already-running timer?

(Removing it means also first checking if it exists every time... since :remove throws an error if it doesn't.)

Thanks in advance! I have a ton of timers in Outside Parties, and skipping that would clean up the code nicely!

3

Yes, it is necessary, as there would be no way for the original timer to know you had reassigned your variable to a newly-created timer.

You could create a convenience function to make the removal logic a bit less verbose. Something like

local function replaceTimer(oldTimer, duration, callback)
	oldTimer:remove()
	oldTimer = playdate.timer.new(duration, callback)
end

However, I wonder if it would make more sense to call playdate.timer:reset() and adjust the duration and timerEndedCallback properties, rather than re-assigning your variable to a new timer?

You could create a function for that too:

function playdate.timer:resetWithDurationAndCallback(duration, callback)
	self:reset()
	self.duration = duration
	self.timerEndedCallback = callback
end

That way other aspects of the timer would be preserved (for instance, if you had set repeats to true) if that's desirable.

(just to note: you can call :remove() again on an already-removed timer, just not on nil, because you can't call a method on nil)

2 Likes
5

Thanks! Yeah—that check for nil seems to be needed just for the moment that FIRST creates a given timer.