UILabel text not being updated

Question

I am unable to change the UILabel text. The code for the the UILabel inside viewDidLoad is :

startLabel=[[UILabel alloc] initWithFrame:CGRectMake(75, 395, 200, 30)];
startLabel.text=@"Recording Sound ...";
startLabel.backgroundColor=[UIColor clearColor];
startLabel.textColor=[UIColor whiteColor];
startLabel.font=[UIFont boldSystemFontOfSize:17];

[self.view addSubview:startLabel];

Later, if I want to change the label of the text with the following code, its not changing on the app :

startLabel.text=@"Searching Database ...";

or

[startLabel setText:@"Searching Database ..."];

The UILabel is not empty, I printed it out during debugging and it shows :

(gdb) po startLabel
<UILabel: 0x2c1a30; frame = (75 395; 200 30); text = 'Searching Database ...'; 
clipsToBounds = YES; userInteractionEnabled = NO; layer = <CALayer: 0x2ae8f0>>

So, the text of the label changes inside the UILabel, but its not updated on the screen.

Can anyone kindly let me know what I am missing here ? Thanks.

Edit 1: I tried performSelectorOnMainThread: - didnt work for me. Edit 2: I am using AVFoundation and ASIHTTP classes to record sound and upload the recorded file here. Nothing else. Didnt use any thread.

Answer 1

You may be facing an issue with threading as mentioned in the comments above. If you have a method that runs on the main thread and does some activity (such as search a database), updates that you make to the UI will not be committed until the run loop gets control. So, if you have a long, time consuming task going on on the main thread, run this code after setting the text of the label:

- (void)doSomethingTimeConsuming
    ... consume some time ...
    ... set text of label ...
    [[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.5]];
    ... continue long operation ...
}

This should flush out any UI changes that you have made. Although this may be a sensible and functional hack, it doesn't beat the alternative. I highly suggest that you perform your app's time consuming tasks on a background thread, and update the UI through the main thread using performSelectorOnMainThread:withObject:waitUntilDone:. See Apple's page on iOS Thread Management.

Answer 2

In my case the function that was updating was called from a touch recognizer on a thread, but the place in the function where I'm changing the value of the label's text property I put it back on the main thread:

dispatch_async(dispatch_get_main_queue(), ^{
    [self.someLabel setText:someString];
});

Answer 3

I had a UILabel showing a level number that would not update to the new level number on a UIViewController. The only viable solution I could find that worked was to call setNeedsDisplay on the main thread of the view controller that owned the UILabel

-(void)changeLevelLabel:(int)theLevel {
dispatch_async(dispatch_get_main_queue(), ^{
    self.levelLabel.text = [NSString stringWithFormat:@"%d",theLevel];
    [self.levelLabel setNeedsDisplay];
});

}

See http://iosdevelopmentjournal.com/blog/2013/01/16/forcing-things-to-run-on-the-main-thread/ for a more detailed explanation