Monitoring background Threads

Question

I am trying to monitor a thread that i set running in the background. I need to be alerted when it is finished executing.

- (IBAction) btnGreaterTen_clicked :(id)sender{

    self.searchDistance = [NSNumber numberWithDouble : 10];

    CGRect frame = CGRectMake (120.0, 185.0, 80, 80);

    activity = [[UIActivityIndicatorView alloc] initWithFrame: frame];
    activity.activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;


    [navigationUpdateFromDetail.window addSubview: activity];


    [activity startAnimating];


    thread = [[NSThread alloc] init];
    [thread start];

[self performSelectorInBackground: @selector (getSetDisplay) withObject:nil];         

if(thread.isFinished == YES){
    [activity stopAnimating];
}
 }

The above code what i have after trying different set up in order to achieve the end result. I am trying to animate the UIActivityIndicator while I use that method "getSetDisplay" to grab information from the net.

The function is good, but the Activity indicator was not coming up. I was told that i needed to run the process on a background thread and the animation on the main thread. My problem now is how do I monitor for when this process is done to stop the activity indicator. thank you in advance

Answer 1

You should consider the problem from a different angle: you should let your "main thread" continue to run, and let your "secondary thread" call a selector on the main thread when it is done doing work.

To accomplish this, you should use the performSelectorOnMainThread method, and call it from your secondary thread. Its prototype is - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait. You should put your "finishing" code in a method, and then do something like:

[self performSelectorOnMainThread:@selector(doneDoingWork) withObject:nil waitUntilDone:NO];

Answer 2

Thank you guys. I finally got a solution that worked thanks to Mike and his above comment.

- (IBAction) btnGreaterTen_clicked :(id)sender{

self.searchDistance = [NSNumber numberWithDouble : 10];


[activity startAnimating];

NSLog(@" search value after change %@", [searchDistance description]);

[self performSelectorInBackground: @selector (getSetDisplay) withObject: nil];
}

I started the activity indicator on with the "[activity startAnimating]" which runs on the main thread. Then i started my method on a background thread with the "performSelectorInBackground". And at the end of my "getSetDisplay" method, i placed the following statement.

[activity performSelectorOnMainThread: @selector (stopAnimating) withObject:nil   waitUntilDone:NO];

This is just another way to say [activity stopAnimating], which is working on the main thread.

Thank you to all that responded.