Where do I put my loop? - objective-c

Question

I really need some help on where to put this loop:
int timer = 10;
while (timer >= 0) {
[secondsLeft setText:[NSString stringWithFormat:#"%d", timer]];
NSLog(#"%d", timer);
timer--;
sleep(1);
}
Anyways, wherever I put this loop I get some sort of error except for under the IBAction where it works perfectly except it delays the button press by 10 seconds :P
Here's my .m file
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
#synthesize answer;
#synthesize secondsLeft;
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
}
- (IBAction)answerButton:(id)sender {
NSString *str = answer.text; // Takes user input from answer.text
int answerOne = [str intValue]; // converts answer into an integer
if(answerOne == 30) {
self.secondsLeftToAnswer.text = #"Correct!";
} else {
self.secondsLeftToAnswer.text = #"You Suck at Math!";
}
}
#end
Anyways can someone please tell me how I can implement this loop into my code so that the loop displays its output to a UILabel (secondsLeft is the UILabel, loop is supposed to display a countdown from 10 to 0 in the UILabel) ?
EDIT: How would I go about implementing a NSTimer to do what I want (countdown from 10)? I tried to set one up but they are so confusing. Thanks for the help so far Jasarien!

Answer 1

The answer is "nowhere". Cocoa is an event-driven system and such loops stop the main thread from processing events and you won't see the text of the label change and user-interaction will be disabled. See the Main Event Loop documentation for details.
Instead use an NSTimer (for example), which works with the runloop to allow periodic method invocation.

Answer 2

In order to show countdown you need to update the label after specific time.
Below is the code depicting the functionality you want.
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
count = 10;
timer = [NSTimer scheduledTimerWithTimeInterval:1.0
target: self
selector: #selector(handleTimer)
userInfo: nil
repeats: YES];
}
-(void)handleTimer{
if (count >= 0) {
[lblTimer setText:[NSString stringWithFormat:#"%ld",(long)count]];
count--;
}else{
[timer invalidate];
}
}
Hope this will help you. Happy coding :)