Question

This’s my first time I use KVO and I got stuck right away. The problem is that when observeValueForKeyPath get called I’m calling another method in the same class. And that method is just showing an alert view. Simple things I thought, but the alert view dosen’t show.

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object 
                     change:(NSDictionary *)change context:(void *)context
{
    [self beginUpdate];
}


 -(void)beginUpdate
 {
     NSLog(@"Check!");
     UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"message" message:@"Hi" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
     [alert show];
 } 

The log message shows up. The alert message only shows if I call it from any other method than observeValueForKeyPath.

Answer 1

As far as I know, observeValueForKeyPath: is called in the context of the thread that modified the observed object. On the other hand, changes to the UI must only be done on the main thread. Try

dispatch_async(dispatch_get_main_queue(), ^{
    [self beginUpdate];
});

or

[self performSelectorOnMainThread:@selector(beginUpdate) withObject:nil waitUntilDone:NO]

to ensure that the UIAlertView is created on the main thread.