Detect UI actions outside of main thread

Question

Note: This question is related to Warn on calls to UIKit from background threads but does not give an answer on two of the approaches below.

I have a problem where the a

Answer 1

Xcode 9 and later

Xcode 9 introduces a Main thread checker which sniffs for many relevant issues potentially performed out-of-main thread. You can enable this analyser the usual way in your Scheme options along with other runtime analysers.

Xcode 8.3 and earlier

Alternative, Xcode-way solution based on steipete's gist – symbolic breakpoint:

You can easily add breakpoints for some other methods on any UIKit class, like -[UIView setNeedsDisplay] etc.