Question

I have some code as shown below:

- (IBAction)startButtonPressed:(id)sender {
    statusText.text = @"Processing...";

    //here I do a bunch of calculations

    //display calculated data
    statusText.text = [[NSString alloc] initWithFormat:@"coefficient: %.4f",
         [[coefficientEstimatesR objectAtIndex:0] doubleValue]];
}

The calculations that I do take about 17s, so I’d like to display the word “processing” while this is being done. However, when I run this, “processing” is never displayed, only the calculated data is displayed.

Any ideas on how to do this would be appreciated.
Thanks!

Answer 1

Do not do any processing in the GUI thread, not when it takes one second, and especially not when it takes 17 seconds. Using GCD makes offloading the task trivial:

- (IBAction)startButtonPressed:(id)sender {
    statusText.text = @"Processing...";

    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        //here I do a bunch of calculations

        dispatch_async(dispatch_get_main_queue(), ^{
            //display calculated data
            statusText.text = [[NSString alloc] initWithFormat:@"coefficient: %.4f",
                               [[coefficientEstimatesR objectAtIndex:0] doubleValue]];
        });
    });
}