Re: Adding 30 minutes to an NSDate
Re: Adding 30 minutes to an NSDate
- Subject: Re: Adding 30 minutes to an NSDate
- From: Nicko van Someren <email@hidden>
- Date: Wed, 20 Jul 2005 10:11:46 +0100
On 20 Jul 2005, at 10:02, j o a r wrote:
On 20 jul 2005, at 10.54, Nicko van Someren wrote:
You don't want to just fire after 60 mins from when your last
timer function was triggered. NSTimers can fire late, especially
if the machine is asleep at the time that the timer was supposed
to fire, so firing at Now+60mins will tend to drift; if you want
the timer to go off on the hour where possible this will be bad.
You would of course re-schedule your timers whenever you wake up
from sleep. That's something you always need to do when you use
NSTimer to fire at an absolute time, and not really particular to
how you choose to tackle this problem.
Agreed, but firing at Now + constant will inevitably drift even if
you're not sleeping, so I can see why Uli wanted to add the constant
to the last firing time rather than just wait for an hour from now.
As I recall the docs even comment on this and point out that
repeating timers fire at an offset from the scheduled time rather
than the actual time, to avoid this problem.
Cheers,
Nicko
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