我試圖寫一個簡單的節拍器,每0.25秒播放一次系統聲音。我使用GCD在單獨的線程上播放點擊,但播放不均勻,點擊有時會以兩個快速節拍跟着慢速節拍播放。我記錄了循環中if語句執行的時間以及0.25秒時的右邊。我希望我不必使用音頻隊列服務。有什麼建議麼?簡單的節拍器
- (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) > (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];
}
即使你得到的NSTimer儘可能精確,你就需要火,AVFoundation引入的滯後將會拖延你的時間。它可能足夠接近以便在某些情況下可以接受,但對於節拍器,您將需要更精確的時間。 –