Calculating intervals between events

What is a good way to record time between user events on iPhon开发者_开发知识库e? ie. time between pressing Button_A and Button_B.

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A more accurate way than using [NSDate date] is to use the timestamp property of the UIEvent. To get the UIEvent, make sure you use the two-argument form for the target-action method.

- (IBAction)buttonPressed:(UIButton *)sender event:(UIEvent *)event
{
    NSTimeInterval timestamp = event.timestamp;
    NSTimeInterval secondsSinceLastEvent = timestamp - lastTimestamp;
}

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Well, you can adapt such code to your situation :

NSDate *start = [NSDate date];
//do some stuff
NSLog(@"%f seconds elapsed", [[NSDate date] timeIntervalSinceDate:start]);

For example, write start = [NSDate date]; in your Button_A action, and NSLog(@"%f seconds elapsed", [[NSDate date] timeIntervalSinceDate:start]); in your Button_B action.

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Create an NSDate object when the buttonA was pressed and then whenever the buttonB is pressed get the time elapsed since now by like this:

[[NSDate now] timeIntervalSince:buttonADate];