![runtime: UI API called from background thread: -[UIApplication applicationState] must be used from main thread only - Stack Overflow runtime: UI API called from background thread: -[UIApplication applicationState] must be used from main thread only - Stack Overflow](https://i.stack.imgur.com/fB8FR.png)
runtime: UI API called from background thread: -[UIApplication applicationState] must be used from main thread only - Stack Overflow
SOLVED: Day 39: Course code throws warning "-[UINavigationController tabBarItem] must be used from main thread only" – 100 Days of Swift – Hacking with Swift forums
![已解决】Xcode9提示:runtime UI API called from background thread UIApplication currentUserNotificationSettings must be used from main thread only – 在路上 已解决】Xcode9提示:runtime UI API called from background thread UIApplication currentUserNotificationSettings must be used from main thread only – 在路上](https://www.crifan.com/files/pic/uploads/2018/07/153c8a40fe20feb69475e65823ce8679.png)
已解决】Xcode9提示:runtime UI API called from background thread UIApplication currentUserNotificationSettings must be used from main thread only – 在路上
![UIView setHidden:] must be used from main thread only · Issue #46 · gang544043963/LGPhotoBrowser · GitHub UIView setHidden:] must be used from main thread only · Issue #46 · gang544043963/LGPhotoBrowser · GitHub](https://user-images.githubusercontent.com/13481443/39958928-712f93ea-563c-11e8-9630-e5e7b07a4e81.png)
UIView setHidden:] must be used from main thread only · Issue #46 · gang544043963/LGPhotoBrowser · GitHub
![UITextField.textAlignment must be used from main thread only” Can't reset TextRows in iOS 11 xcode 9.1 · Issue #1351 · xmartlabs/Eureka · GitHub UITextField.textAlignment must be used from main thread only” Can't reset TextRows in iOS 11 xcode 9.1 · Issue #1351 · xmartlabs/Eureka · GitHub](https://user-images.githubusercontent.com/31646541/33939410-18fc3fec-e031-11e7-9877-8fdd1188e7e7.png)
UITextField.textAlignment must be used from main thread only” Can't reset TextRows in iOS 11 xcode 9.1 · Issue #1351 · xmartlabs/Eureka · GitHub
![UIView setHidden:] must be used from main thread only · Issue #46 · gang544043963/LGPhotoBrowser · GitHub UIView setHidden:] must be used from main thread only · Issue #46 · gang544043963/LGPhotoBrowser · GitHub](https://user-images.githubusercontent.com/13481443/39958918-6391ef76-563c-11e8-92e0-ec35bbea24e8.png)