Re: Best pattern to follow for scheduling an event
Re: Best pattern to follow for scheduling an event
- Subject: Re: Best pattern to follow for scheduling an event
- From: Jean-Daniel Dupas <email@hidden>
- Date: Thu, 8 Nov 2007 19:22:26 +0100
Le 8 nov. 07 à 19:05, John Stiles a écrit :
I have a method that needs to schedule a "cleanup pass" to occur in
the near future. The method might be called once, ten times, or a
hundred times in a row, but I only need to clean up one time. To
implement this, I used the following pattern, and I'm wondering if
it was the best way to go.
First, when the object is first created, I create a timer. I
scheduled its fire date to be in the distant, distant future:
m_deferredFixupTimer = [[NSTimer
scheduledTimerWithTimeInterval:DBL_MAX
target:myObject
selector:@selector(doFixUp:)
userInfo:NULL
repeats:YES] retain];
(I considered using INFINITY instead of DBL_MAX, but sometimes
library code isn't prepared to deal with infinite values, so I
figured DBL_MAX is safer and already more than large enough.)
Then, when my method is called, I schedule the timer to fire
immediately:
[m_deferredFixupTimer setFireDate:[NSDate date]];
This defers the fire to the next run-through of the event loop,
which for my purposes is sufficient. It only fires one time.
So is this the right way to do it? It seems to work in practice, it
just seemed a little quirky to me for some reason. I guess it would
make more sense if I could make a timer that's scheduled to never
fire, instead of a timer that's scheduled to repeat and fire once
every trillion years. But in practice it seems to be equivalent.
You can maybe do something like this.
@interface Foo : NSObject {
BOOL shouldClean;
}
@end
- (void)cleanup:(id)arg {
shouldClean = NO;
/* clean */
}
- (void)doSomethingThatRequireCleanup {
if (!shouldClean) {
shouldClean = YES;
/* The aSelector message is sent to target with argument anArgument
at the start of the next run loop iteration */
[[NSRunLoop currentRunLoop] performSelector:@selector(cleanup:)
target:self argument:something order:0 modes:[NSArray
arrayWithObject:NSDefaultRunLoopMode]];
}
/* perform work */
}
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