1、MBProgressHUD *HUD = [[MBProgressHUD alloc] initWithWindow:[UIApplication sharedApplication].keyWindow];
2、MBProgressHUD *HUD = [MBProgressHUD showHUDAddedTo:[[UIApplication sharedApplication].windows objectAtIndex:1] animated:YES];
[self.view.window addSubview:HUD];
HUD.labelText = kVerifyRefreshing;
第一种动画失效，不知啥原因？？？
原文：http://www.cnblogs.com/mengfanrong/p/4170484.html