Question

I am trying to run a NSTimer on a thread using iPhone SDK 3.0. I think I am doing everything correctly (new runloop etc.). If I call [timer invalidate] on viewDidDissappear though I get this error:

bool _WebTryThreadLock(bool), 0x3986d60: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now…
Program received signal: “EXC_BAD_ACCESS”.

Here is my code:

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [activityIndicator startAnimating];
    NSThread* timerThread = [[NSThread alloc] initWithTarget:self selector:@selector(timerStart) object:nil]; //Create a new thread
    [timerThread start]; //start the thread
}

-(void)timerStart
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
    //Fire timer every second to updated countdown and date/time
    timer = [[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(method) userInfo:nil repeats:YES] retain];
    [runLoop run];
    [pool release];
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [timer invalidate];
}

When I remove the line invalidating the timer everything works fine. Am I not supposed to invalidate it or am I making some other mistake?

Thanks

Answer 1

Try

[timer performSelector:@selector(invalidate) onThread:timerThread withObject:nil waitUntilDone:NO];

instead. You will have to make timerThread an ivar of your view controller.