Question

I’m trying to change the enabled property of an UIBarButtonItem after doing some stuff in an NSThread. After pressing the button I set the enabled to NO then perform the threaded part and at the end I try to re enable the button. Fairly basic.

Somehow this fails, however I’m able to change any other property of the the UIBarButtonItem correctly (for ex. title).

What am I doing wrong here?

@interface myViewController : UIViewController <UITableViewDataSource, UITableViewDelegate> {
    IBOutlet UIBarButtonItem *myButton;

}
@property (nonatomic, retain) IBOutlet UIBarButtonItem *myButton;

- (IBAction)mysub:(id)sender;

@end



@implementation myViewController

@synthesize myButton;

- (IBAction)mysub:(id)sender {
 [myButton setEnabled:NO];

    [NSThread detachNewThreadSelector:@selector(mysub_threaded) toTarget:self withObject:nil];    
}

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

    … do threaded stuff

    [myButton performSelectorInBackground: @ selector(setEnabled :) withObject: [NSNumber numberWithBool:YES]];

    [pool drain];
}

Answer 1

You want performSelectorOnMainThread instead.

[myButton performSelectorOnMainThread:@selector(setEnabled:)
                           withObject:[NSNumber numberWithBool:YES]
                        waitUntilDone:NO];

Always do anything that touches the UI on the main thread.

But sometimes passing arguments like this is funky too. I find it best to wrap up everything you need done in another method

- (void)mysub_complete {
  [myButton setEnabled:YES];
}

Then call that with

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

Now you can do as much other UI stuff as you want without worry about it.