How update a label periodically on iOS (every second)? [duplicate]

Answer 1

You could also use GCD. So run

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
    [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateLabel:) userInfo:nil repeats:YES];
});

and now in your updateLabel method

- (void) updateLabel:(id) sender {
    NSString *text = @"some text";
    dispatch_sync(dispatch_get_main_queue(), ^{
        label.text = text;
    });
}

This will update the label in the main thread.

Answer 2

The problem is that a scheduledTimer will not get called while the main thread is tracking touches. You need to schedule the timer in the main run loop.

So instead of doing

[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateLabel:) userInfo:nil repeats:YES];

use

NSTimer* timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:@selector(updateLabel:) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];

Answer 3

try this:

    self.timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:@selector(updateClock) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];