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POSimple Metronome
 

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    <p>I'm trying to write a simple metronome, by playing a system sound every 0.25 seconds. I use GCD to play the clicks on a separate thread but the playing is uneven with the clicks coming sometimes as two quick beats followed by a slower beat. I Logged the time when the if statement in the loop is executed and its right on 0.25 seconds. I'm hoping I don't have to use Audio Queue Services. Any suggestions?</p> <pre><code>- (IBAction)start:(id)sender { dispatch_queue_t clickQueue; // the queue to run the metronome clicker dispatch_queue_t mainQueue; // I access the main queue to demonstrate how to change UIKit items //clickQueue = dispatch_queue_create("clickQueue", NULL); clickQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0); mainQueue = dispatch_get_main_queue(); dispatch_async(clickQueue, ^{ double timeWas = [NSDate timeIntervalSinceReferenceDate]; //delay by a 1/10 of a second so the first few clicks don't bunch up. double timeIs = [NSDate timeIntervalSinceReferenceDate] - 0.1; // playing starts out as NO because it gets switched at the end of the loop // and the PlaySystemSound block isn't off the queue yet. There is probably a // better way to do this. while (playing) { timeIs = [NSDate timeIntervalSinceReferenceDate] ; if ((timeIs - timeWas) &gt; (60.0/240)) { AudioServicesPlaySystemSound(sound); timeWas = timeIs; // I want to flast the 200 label between orange and black but I have to access // user interface objects from the queue that they are running in, usually the // main queue. dispatch_async(mainQueue, ^{ if (flash) [bpm setTextColor:[UIColor orangeColor]]; else [bpm setTextColor:[UIColor blackColor]]; flash = !flash; }); } } }); playing = !playing; if (playing) [startButton setTitle:@"Stop" forState:UIControlStateNormal]; else [startButton setTitle:@"Start" forState:UIControlStateNormal]; } </code></pre>
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