无法使计时器无效

Question

I am trying to use a timer in my application where I want to start a timer on viewWillAppear and want to stop it in the viewWillDisappear method. I have done following coding:
in .h: @property (nonatomic, strong) NSTimer *timer;

-(void)viewWillAppear:(BOOL)animated{
   [super viewWillAppear:FALSE];
   if(!_timer){
     _timer = [NSTimer scheduledTimerWithTimeInterval: 5.0
                                              target: self
                                            selector:@selector(reloadInboxMessages)
                                            userInfo: nil repeats:YES];
  }
}

-(void)reloadInboxMessages {
  NSLog(@"reloadInboxMessages");
  [tblvwMessage reloadData];
 }

-(void)viewWillDisappear:(BOOL)animated {
   [super viewWillDisappear:FALSE];

   NSLog(@"viewWillDisappear");
   if([_timer isValid]){
       [_timer invalidate];
       _timer = nil;
   }
}

I thought it would be simple task to do but I am not sure why it is not working. What is the issue?

Answer 1

尝试self.timer = [NSTimercheduledTimerWithTimeInterval ...

Answer 2

There are three ways to create a timer:

Use the scheduledTimerWithTimeInterval:invocation:repeats: or scheduledTimerWithTimeInterval:target:selector:userInfo:repeats: class method to create the timer and schedule it on the current run loop in the default mode.

Use the timerWithTimeInterval:invocation:repeats: or timerWithTimeInterval:target:selector:userInfo:repeats: class method to create the timer object without scheduling it on a run loop. (After creating it, you must add the timer to a run loop manually by calling the addTimer:forMode: method of the corresponding NSRunLoop object.)

Allocate the timer and initialize it using the initWithFireDate:interval:target:selector:userInfo:repeats: method. (After creating it, you must add the timer to a run loop manually by calling the addTimer:forMode: method of the corresponding NSRunLoop object.)

EDIT:

You are using method which already adds it to mainLoop from - create a timer with second approach and leave manual adding.

You must send invalidate message from the thread on which the timer was installed. If you send this message from another thread, the input source associated with the timer may not be removed from its run loop, which could prevent the thread from exiting properly.

EDIT:

to invalidate the timer that is passed in the callback, but that won't occur within viewWillDisappear method:. therefore, it doesn't quite apply in this scenario:

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

Hope it helps.