Question

I’m very very new to iOS programming but I already have a big issue I can’t solve. It seems so easy.

I have a button, I click on it to change a label called message

Here is the code:

- (IBAction)react:(id)sender {
    int hasard ;
    hasard=3; 
    message.text=[NSString stringWithFormat:@"1 %d",hasard];    
    sleep (1);
    message.text=[NSString stringWithFormat:@"2 %d",hasard]; 
}

It works well but I don’t see the first message.text change.
When I click the button, I have to wait one second and I see 2 3

I thought I could see 1 3, wait a second and then see 2 3.
What is missing? It seems so obvious.

Answer 1

You are blocking the main thread (well, rather sleep() blocks it). If you do so, committed changes to the UI won’t appear – you’ll only see the final result. You have to do something else (blocking the UI is a very bad idea in terms of user experience, by the way). You can try using a timer, for example:

int hasard = 3;

- (void)react:(id)sender
{
     message.text = [NSString stringWithFormat:@"1 %d", hasard];
     [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(timer:) userInfo:nil repeats:NO];
}

- (void)timer:(NSTimer *)tmr
{
     message.text = [NSString stringWithFormat:@"2 %d", hasard];
}