监听音量的按键

- (void)addVolumeObserver
{
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    NSError *error = nil;
    [audioSession setActive:YES error:&error];
    if (error) {
        NSLog(@"%@", error);
    }
    [audioSession addObserver:self forKeyPath:@"outputVolume" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    if (![keyPath isEqualToString:@"outputVolume"]) {
        return;
    }
    
    if (self.start == nil) {
       // 时间1
        NSDate *date1 = [NSDate date];
        NSTimeZone *zone1 = [NSTimeZone systemTimeZone];
        NSInteger interval1 = [zone1 secondsFromGMTForDate:date1];
        self.start = [date1 dateByAddingTimeInterval:interval1];
    }
    
    self.timeCount ++;
    NSKeyValueChangeKey newValue = change[@"new"];
    NSKeyValueChangeKey oldValue = change[@"old"];
    NSLog(@"oldValue=%@ newValue=%@", oldValue, newValue);
    
    // 时间2
    NSDate *date2 = [NSDate date];
    NSTimeZone *zone2 = [NSTimeZone systemTimeZone];
    NSInteger interval2 = [zone2 secondsFromGMTForDate:date2];
    self.end = [date2 dateByAddingTimeInterval:interval2];
    
    double intervalTime = [self.end timeIntervalSinceReferenceDate] - [self.start timeIntervalSinceReferenceDate];
    NSLog(@"时间差 = %f", intervalTime);
    if (intervalTime > 5.0) {
        [self resetCount];
        return;
    }
    
    if (self.timeCount == 3) {
        NSLog(@"AlertShow");
        [self resetCount];
        [self showAlertView];
    }
}