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iOS - In which queue selectors run on by default?

Suppose, I am presenting an UIAlertController, say myAlert, from main tread. myAlert has a action, defaultAction. I wonder if defaultActions handler by default runs on main queue or not. In other words, I wonder if there are some UI related operation inside doStuff in below code, am I required to wrap these UI tasks with main queue or it is guaranteed to run in main queue by OS?

UIAlertController* myAlert = [UIAlertController alertControllerWithTitle:@"My Alert"
                               message:@"This is an alert."

UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
   handler:^(UIAlertAction * action) {
      doStuff() // should I wrap doStuff in main queue, if doStuff has ui operations?

[alert addAction:defaultAction];
[self presentViewController:alert animated:YES completion:nil];
like image 494
Sazzad Hissain Khan Avatar asked Mar 10 '23 09:03

Sazzad Hissain Khan

1 Answers

You are actually asking if it runs on the main queue, not if it is thread safe.

An object is "thread safe" if it can be accessed/modified from multiple threads without issue.

The answer to your question is that the action closure will run on the main queue as it results from a user interaction, so you do not need to explicitly dispatch UI updates onto the main queue.

like image 129
Paulw11 Avatar answered Mar 12 '23 02:03