iOS筆記：This application is modifying the autolayout engine from a background thread...

全Log：This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.

原意：你在非主線程動到了UI，可能會造成崩潰。
只要有UI前綴的，包含AlertView類跳窗，更改任何參數都要在主線程

dispatch_async(dispatch_get_main_queue(), ^{
    [self updateUI];
});