warning：This application is modifying the autolayout engine from a background thread

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.

错误缘由：在回调函数中或者后台线程中更新了UI界面，而UI界面必须是在主界面中才能进行修改

解决办法：

dispatch_async(dispatch_get_main_queue(), ^{

      <your code>

});