How to fix "exc_bad_instruction (code=exc_i386_invop subcode=0x0)" - ios

Question

I want to make a timer in my app, but i find a problem like this:
My code run very well at viewController which contain the code below, but after i dismiss this viewController a few seconds, Xcode will report an erro: exc_bad_instruction (code=exc_i386_invop subcode=0x0
If i didn't use dispatch_suspend(self.timer) and dispatch_resume(self.timer), everything will be ok
otherwise, I can see the error will happen when Xcode deal with [viewController .cxx_destruct]
so, anyone can tell me how to fix it?
Thank you
Here is my code,
- (void)timeButtonClick:(UIButton *)button{
if (self.isTiming == YES){
self.isTiming = NO;
self.executeTime = [self.timeButton currentTitle];
dispatch_suspend(self.timer);
}else if (self.isTiming == NO){
self.isTiming = YES;
self.createDate = [NSDate date];
dispatch_resume(self.timer);
}
}
- (dispatch_object_t)timer{
if (_timer == nil) {
dispatch_queue_t timerQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, timerQueue);
dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
__weak typeof (self)weakSelf = self;
dispatch_source_set_event_handler(timer, ^{
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = #"HH:mm:ss";
NSCalendar *calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
NSCalendarUnit unit = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDate *currentDate = [NSDate date];
NSDateComponents *currentCmps = [calendar components:unit fromDate:weakSelf.createDate toDate:currentDate options:NSCalendarWrapComponents];
NSDate *executeTime = [dateFormatter dateFromString:weakSelf.executeTime];
NSDateComponents *executeCmps = [calendar components:unit fromDate:executeTime];
NSString *newExecuteTime = [NSString stringWithFormat:#"%02ld:%02ld:%02ld", executeCmps.hour + currentCmps.hour, executeCmps.minute + currentCmps.minute, executeCmps.second + currentCmps.second];
dispatch_async(dispatch_get_main_queue(), ^{
[weakSelf.timeButton setTitle:newExecuteTime forState:UIControlStateNormal];
});
});
_timer = timer;
}
return _timer;
}

Answer 1

Move your timer to another place like AppDelegate, you are getting this error because you are dispatching the timer to another thread, then when the VC is dismissed the timer wants to set the title to timeButton which wa salready destroyed when the VC was dismissed.
You could also try to make a strong weakself, but I really suggest you to move the timer code to another class.