ios - Main Thread Checker: UI API called on a background thread: -[UIApplication delegate] Freezes the application

Question

Whenever my application fetch data from JSON it sometimes get this warning and application freezes right away:

Main Thread Checker: UI API called on a background thread: -[UIApplication delegate]

PID: 7439, TID: 362794, Thread name: (none), Queue name: NSOperationQueue 0x60000002f7c0 (QOS: UNSPECIFIED), QoS: 0 Backtrace:

Can anyone explain how to get rid of it?

Answer 1

It looks like you're updating something on the UI from a thread that's not the main thread.

There's not a lot to go on in your question. But if you're using JSON, you're probably retrieving it asynchronously. Make sure that whenever you update the UI from something retrieved, that you wrap it up in a call to the main thread through something like

dispatch_async(dispatch_get_main_queue(), ^{
// code to post to UI
});