初始化MBProgressHUD:
UIWindow *window = [[UIApplication sharedApplication] keyWindow]
_hud = [[MBProgressHUD alloc]initWithWindow:window];
_hud.dimBackground = bDim;
_hud.labelText = message;
[window addSubview:_hud];
[_hud show:YES];
但是有时_hub不显示。不知道哪里出问题了?