How to solve: This application is modifying the autolayout engine from a background thread

Question

This error is logged to the console when some part of the code is changing UI items from other threads than the main thread. But how can I find where it does this?

Answer 1

Main problem with "This application is modifying the autolayout engine from a background thread" is that it seem to be logged a long time after the actual problem occurs, this can make it very hard to troubleshoot.

I managed to solve the issue by creating three symbolic breakpoints.

Debug > Breakpoints > Create Symbolic Breakpoint...

Breakpoint 1:

• Symbol: -[UIView setNeedsLayout]

• Condition: !(BOOL)[NSThread isMainThread]

Breakpoint 2:

• Symbol: -[UIView layoutIfNeeded]

• Condition: !(BOOL)[NSThread isMainThread]

Breakpoint 3:

• Symbol: -[UIView updateConstraintsIfNeeded]

• Condition: !(BOOL)[NSThread isMainThread]

With these breakpoints, you can easily get a break on the actual line where you incorrectly call UI methods on non-main thread.