👀 Views: 496 💬 Answers: 1 📅 Created: 2025-06-19

ios objective-c gcd Objective-C

I'm trying to figure out I'm stuck on something that should probably be simple. I'm stuck on something that should probably be simple. I'm stuck on something that should probably be simple. I've looked through the documentation and I'm still confused about I'm working with a crash in my Objective-C app when I try to update UI components from a background thread. I have a method that fetches data from a remote server and parses it using GCD. Here’s a simplified version of my code: ```objc dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // Fetch data from server NSData *data = [self fetchDataFromServer]; NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 behavior:nil]; NSString *title = json["title"]; // Attempting to update UI on background thread self.titleLabel.text = title; }); ``` When I run this code, I receive the following behavior message in the console: ``` *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to set property 'text' of 'UILabel' on a background thread. This is not allowed.' ``` I know that UI updates should be performed on the main thread, but I'm not sure how to properly switch back to the main thread after fetching the data. I’ve tried wrapping the UI update code in a `dispatch_async` block like this: ```objc dispatch_async(dispatch_get_main_queue(), ^{ self.titleLabel.text = title; }); ``` However, I'm still getting the same crash. I've double-checked that I'm not calling any UI updates before switching to the main queue. Could someone guide to understand what I'm missing here? Is there a specific way I should be structuring my GCD calls to ensure that UI updates happen safely? Any insights would be greatly appreciated! I'm working on a web app that needs to handle this. I'd really appreciate any guidance on this. What's the best practice here? What am I doing wrong? Any advice would be much appreciated. Could this be a known issue? I'm developing on Ubuntu 20.04 with Objective-C.