从线程调用委托方法

Question

I've this bit of code:

- (IBAction)registerAction:(id)sender {
 [NSThread detachNewThreadSelector:@selector(registerThread) toTarget:self withObject:nil];
}

- (void)registerThread {
 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];  

 MyDelegate *delegate = (MyDelegate *)[[UIApplication sharedApplication] delegate];


 NSInteger locationID = [delegate.api checkCoordinate:[NSString stringWithFormat:@"%f,%f",
             location.coordinate.latitude, location.coordinate.longitude]];

 NSNumber *status = [api registerWithUsername:usernameField.text 
          password:passwordField.text email:emailField.text andLocation:locationID];

 [self performSelectorOnMainThread:@selector(registrationDoneWithStatus:) withObject:[NSNumber numberWithInt:1] waitUntilDone:NO];  
    [pool release];   
}

it works nicely, but sometimes I get this error:

void _WebThreadLockFromAnyThread(bool), 0x6157e30: Obtaining the web lock from a thread other than the main thread or the web thread. UIKit should not be called from a secondary thread.

And it seems that only using the delegate I get this error, and I don't know how to resolve.

Thanks in advance :)

Answer 1

I've run into the same problem recently.

There may be some active views (eg. UITextField , UITextView ). Try resignFirstResponder those views before accessing delegate

Answer 2

You fix the problem by very carefully thinking through your application's concurrency architecture and ensuring that you aren't exercising anything from a thread that should only be done on the main thread.

In this case, you are causing the UIKit to execute code from a secondary thread. If you were to set a breakpoint on _WebThreadLockFromAnyThread, you would know exactly where.

It is exceedingly atypical to use the app's delegate from a secondary thread in anything but the most extremely controlled circumstances.

tl;dr You can't make an app threaded by detaching a new thread against a random selector.