Question

I’m displaying 10 questions in a view controller. I want to calculate the time taken to answer those questions.Means I want to set time count down after the time reaches to zero I want to display an alert. Please help me.

Thanks in advance.

Answer 1

You seems to want 2 things.

One is elapsed time between the start of the question until it get answer, you can do that with:

NSDate *now = [NSDate date];
NSTimeInterval *elapsedTime = [now timeIntervalSinceNow];

Reference:
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSDate_Class/Reference/Reference.html

The second is to use NSTimer for counting down. You can do that with the following code:

NSTimer *theTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(countdownTracker:) userInfo:nil repeats:YES];
// Assume a there's a property timer that will retain the created timer for future reference.
self.timer = theTimer;
// Assume there's a property counter that track the number of seconds before count down reach.
self.counter = 10;

The method that will be invoked by timer.

- (void)countdownTracker:(NSTimer *)theTimer {
    self.counter--;
    if (self.counter < 0) {
        [self.timer invalidate];
        self.timer = nil;
        self.counter = 0;
        [[[[UIAlertView alloc] initWithTitle:@"Countdown" message:@"Countdown completed." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease] show];
    }
}

This should work.

Reference:
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSTimer_Class/Reference/NSTimer.html