while a presentation or dismiss is in progress

当使用presentViewController和dismissPresentViewController时，如果报这个错 : while  presentation is in progress ，修改方法为[mainView dismissModalViewControllerAnimated:NO];  将参数Animated改为NO；如果报这个错while a presentation or dismiss is in progress，试试这样

 if (![[mainView modalViewController] isBeingDismissed]) {
        [mainView dismissModalViewControllerAnimated:NO];
    }