NSTimer Will Not Invalidate - objective-c

Question

-(IBAction) loadWeb: (id) sender {
[_webView loadRequest:nsrequest2];
_webView1.hidden = YES;
_webView.hidden = NO;
self.checkForAdd = [NSTimer scheduledTimerWithTimeInterval:0.4
target:self selector:#selector(checkForAddToCart:) userInfo:nil
repeats:YES];
}
-(IBAction)button1:(id)sender {
[self.checkForAdd invalidate];
}
How would I invalidate the timer? I have tried it without self and many other ways, but for some reason, when I press the button the timer does not invalidate.

Answer 1

Check if loadWeb: is called multiple times. If it is, you will have old timers running without having a reference to them so you can't invalidate them. You should have [self.checkForAdd invalidate]; before you create the new timer.
When you do invalidate the timer, if you aren't creating a new one, set self.checkForAdd = nil; to be sure you aren't going to try using the timer again (some actions will throw an exception if you do).
If at any point you do self.checkForAdd = nil; without having invalidated the timer then you won't have a reference to it so you won't be able to invalidate it in the future.

Answer 2

According to your code, loadWeb is being trigger by a button. So you will be creating new timer every time when button will be press. Its better you create timer on some where else, like create in init, or in viewDidLoad method, because if you are creating this here, you have to make sure you are not creating timer again and again. You can do this by doing a if check
if(!self.checkForAdd){
self.checkForAdd = [NSTimer scheduledTimerWithTimeInterval:0.4
target:self selector:#selector(checkForAddToCart:) userInfo:nil
repeats:YES];
}
Right now its creating new timer on button tap, and previous one have no reference.