Question

I want to update a label on an iPhone form from a separate thread. The thread is running but the label is not updated.

here is my code

-(void)launchThread:(id)param;
@property (weak, nonatomic) IBOutlet UILabel *timeLabel;

...

-(void) launchThread:(id)param{
UILabel *control = (UILabel*)param;
NSMutableString *str;
for (int i=0; i<1000; i++) {
    str = [NSMutableString stringWithFormat:@"%d",i];
    control.text=str;
    NSLog(@"%@",str);
    sleep(1);
}}

...

- (void)viewDidLoad {
    [super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
    [NSThread detachNewThreadSelector:@selector(launchThread:) toTarget:self withObject:timeLabel];
}

I guess the label’s text is updated but not refreshed on the form. How do I refresh it?

I have tried to look for similar posts but they did not work for me. Sorry if I repeated the question.

Answer 1

@jackslash is correct, you can only update the interface on the main thread (UI thread). I would suggest using performSelectorOnMainThread to update your UILabel. I think the syntax is something like:

[self.label performSelectorOnMainThread : @ selector(setText : ) withObject:str waitUntilDone:YES];

Not quite certain tho. Do some googling and you should be able to find a working example with it.