目标C：计时器在再次打开时使应用程序崩溃

Question

I have my NSTimer declared in the header file. When the play button is tapped, it turns on the timer. Next tap disables timer. A third tap crashes the app with no error message. Why would this be happening?

-(IBAction) play {

if ([col1 isValid]) {
    [col1 invalidate];
} else {
    col1 = [NSTimer scheduledTimerWithTimeInterval:.8 target:self selector:@selector(playCol1) userInfo:nil repeats:YES];
}

Answer 1

invalidate will cause the object to be released. So, you are attempting to call isValid on a bad reference. nil out the col1 object after you invalidate it, and you should be fine.

-(IBAction) play {

    if ([col1 isValid]) {
        [col1 invalidate];
        col1 = nil;
    } else {
        col1 = [NSTimer scheduledTimerWithTimeInterval:.8 target:self selector:@selector(playCol1) userInfo:nil repeats:YES];
}

Answer 2

Crash is because it is trying to invalidate an already invalidated timer col1 .

Did you try [col1 isValid]==YES ? Try out that and if that doesn't work then try using an custom integer or BOOL type flag.

I had a similar problem with the isValid Method and made a workaround for it by using flag of BOOL type

Hope this helps you.

SAMPLE OF USAGE OF CUSTOM FLAGS:

 BOOL invalidateTimer = NO; 
-(IBAction) play 
{
     if (invalidateTimer == YES) 
     {
                 [col1 invalidate];
     }
     else if (invalidateTimer == NO)
     {
           col1 = [NSTimer scheduledTimerWithTimeInterval:.8 target:self selector:@selector(playCol1) userInfo:nil repeats:YES];
           invalidateTimer = YES;
     }
}