遇到程式掛掉，發出的錯誤訊息：

This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes.

聽說可以用解法：

Swift 3

 DispatchQueue.main.async {
    // Update UI
 }

Swift Version < 3

dispatch_async
 
(dispatch_get_main_queue(){
    // code here
})

Objective-C Version

dispatch_async(dispatch_get_main_queue(), ^{
    // code here
});