警告提示：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.
錯誤原因：在回調函數中或者后台線程中更新了UI界面，而UI界面必須是在主界面中才能進行修改
解決辦法：
dispatch_async(dispatch_get_main_queue(), ^{
<your code>
});