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

Question

I am using google maps in Xcode 9 beta, iOS 11.

I am getting an error outputted to the log as follows:

Main Thread Checker: UI API called on a

Answer 1

It's hard to find the UI code which is not executed in main thread sometimes. You can use the trick below to locate it and fix it.

1. Choose Edit Scheme -> Diagnostics, tick Main Thread Checker.

   Xcode 11.4.1

   Click the small arrow next to the Main Thread Checker to create a Main Thread Checker breakpoint.

   Previous Xcode

   Tick on Pause on issues.

2. Run your iOS application to reproduce this issue. (Xcode should pause on the first issue.)

3. Wrap the code that modify the UI in DispatchQueue.main.async {}