iPhone dev -- performSelector:withObject:afterDelay or NSTimer?

Question

To repeat a method call (or message send, I guess the appropriate term is) every x seconds, is it better to use an NSTimer (NSTimer's scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:) or to have the method recursively call itself at the end (using performSelector:withObject:afterDelay)? The latter doesn't use an object, but maybe its less clear/readable? Also, just to give you an idea of what I'm doing, its just a view with a label which counts down to 12:00 midnight, and when it gets to 0, it will blink the time (00:00:00) and play a beep sound forever.

Thanks.

Edit: also, what would be the best way to repeatedly play a SystemSoundID (forever) ? Edit: I ended up using this to play the SystemSoundID forever:

// Utilities.h
#import <Foundation/Foundation.h>
#import <AudioToolbox/AudioServices.h>


static void soundCompleted(SystemSoundID soundID, void *myself);

@interface Utilities : NSObject {

}

+ (SystemSoundID)createSystemSoundIDFromFile:(NSString *)fileName ofType:(NSString *)type;
+ (void)playAndRepeatSystemSoundID:(SystemSoundID)soundID;
+ (void)stopPlayingAndDisposeSystemSoundID;

@end


// Utilities.m
#import "Utilities.h"


static BOOL play;

static void soundCompleted(SystemSoundID soundID, void *interval) {
    if(play) {
        [NSThread sleepForTimeInterval:(NSTimeInterval)interval];
        AudioServicesPlaySystemSound(soundID);
    } else {
        AudioServicesRemoveSystemSoundCompletion(soundID);
        AudioServicesDisposeSystemSoundID(soundID);
    }

}

@implementation Utilities

+ (SystemSoundID)createSystemSoundIDFromFile:(NSString *)fileName ofType:(NSString *)type {
    NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:type];
    SystemSoundID soundID;

    NSURL *filePath = [NSURL fileURLWithPath:path isDirectory:NO];

    AudioServicesCreateSystemSoundID((CFURLRef)filePath, &soundID);
    return soundID;
}

+ (void)playAndRepeatSystemSoundID:(SystemSoundID)soundID interval:(NSTimeInterval)interval {
    play = YES
    AudioServicesAddSystemSoundCompletion(soundID, NULL, NULL,
                                          soundCompleted, (void *)interval);
    AudioServicesPlaySystemSound(soundID);
}

+ (void)stopPlayingAndDisposeSystemSoundID {
    play = NO
}

@end

Seems to work fine.. And for the label blinking I'll use an NSTimer I guess.

Answer 1

A timer is more suited to a strictly defined interval. You will lose accuracy if you have your function call itself with a delay because its not really synced to a time interval. There's always the time taken to run the actual method itself as well which puts the interval out.

Stick with an NSTimer, I'd say.