Question

I’m trying to set up a view that gives feed back via progress bar while it carries out a task, by incrementally sending updates to the view.

I don’t know much about multithreading, so I’m trying to do this without using it. Is there a way to force a view to update? It seems like there should be something to do this, cause I’m not really waiting for input, just giving output, and things happen one at a time – carry out computation steps, update progress bar, carry out more steps, update bar, etc.

Thanks for any help with this.

Answer 1

Easiest way is to divide the task into small chunks and perform them on a timer so the runloop can process UI events:

static NSMutableArray *tasks;

- (void)addTask:(id)task
{
    if (tasks == nil)
        tasks = [[NSMutableArray alloc] init];
    [tasks addObject:task];
    if ([tasks count] == 1)
        [self performSelector:@selector(executeTaskAndScheduleNextTask) withObject:nil afterDelay:0.0];
}

- (void)executeTaskAndScheduleNextTask
{
    id task = [tasks objectAtIndex:0];
    [tasks removeObjectAtIndex:0];
    // Do something with task
    NSLog(@"finished processing task: %@", task);
    // Sechedule processing the next task on the runloop
    if ([tasks count] != 0)
        [self performSelector:@selector(executeTaskAndScheduleNextTask) withObject:nil afterDelay:0.0];
}

^{A background thread makes for a much better user experience though, and may actually be simpler depending on what operation you are performing.}