Question

I don’t want to create NSTimer object. How do I invalidate timer? I want to invalidate timer in viewWillDisappear.

-(void) viewDidLoad
{ 
 [super viewDidLoad];
 [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:@selector(onTimer:) userInfo:nil repeats:YES];
}

Answer 1

A

you have to hold on to the timer you create:

@interface MONObject ()
@property (nonatomic, retain) NSTimer * timerIvar;
@end

@implementation MONObject
...
- (void)viewDidLoad
{ 
 [super viewDidLoad];
 self.timerIvar = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:@selector(onTimer:) userInfo:nil repeats:YES];
}

- (void)invalidateTimer
{
  [self.timerIvar invalidate];
  self.timerIvar = nil;
}

- (void)viewWillDisappear:(BOOL)animated
{
  ...
  [self invalidateTimer];
}

B

another option would be to invalidate the timer that is passed in the callback, but that won’t occur within viewDidUnload:. therefore, it doesn’t quite apply in this scenario:

- (void)onTimer:(NSTimer *)pTimer
{
  [pTimer invalidate];
}