NSProgressIndicator progress with For loops?

Question

My application does a lot of work with a bunch of For loops. It calculates a massive amount of strings, and it can take over a whole minute to finish.

So I placed a NSProgressIndicator in my app.

Within the loops, I used the "incrementBy" function of the NSProgressIndicator. However, I don't see the actual bar filling up.

I suspect that's because of the loops taking all power possible, and thus the NSProgressIndicator is not updated (graphically).

How would I make it progress then?

Answer 1

Are your for loops running on the main thread or in a background thread? If they're running on the main thread, the GUI will never get a chance to update itself to reflect the progress change as this will only happen at the end of the runloop, i.e. after your functions have finished running.

If your for loops are running in the background, you're being naughty! You shouldn't update the GUI from anywhere but the main thread. If you're targeting a modern system, you can use GCD to trivially work around this.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {
    for (int i = 0; i < n; i++) {
        // do stuff
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            // do your ui update here
        });
    }
});

Alternatively, you can rewrite your for loops to take advantage of GCD even further and use dispatch_apply. The equivalent of the above would be:

dispatch_apply(n, DISPATCH_QUEUE_PRIORITY_DEFAULT, ^(size_t i) {
    // for loop stuff here
    dispatch_async(dispatch_get_main_queue(), ^(void) {
        // do your ui update here
    });
});

Note that using dispatch_apply means that each "iteration" of the loop may run concurrently with respect to one another, so this won't be applicable if your for loop requires to be run in a serial fashion.