while a presentation or dismiss is in progress

當使用presentViewController和dismissPresentViewController時，如果報這個錯 : while  presentation is in progress ，修改方法爲[mainView dismissModalViewControllerAnimated:NO];  將參數Animated改爲NO；如果報這個錯while a presentation or dismiss is in progress，試試這樣

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