presentViewController的modalPresentationStyle问题:
首先我们查看一下UIModalPresentationStyle，对比以前的看看有什么变化没有。发现新增了一个枚举值UIModalPresentationAutomatic，默认的就是这个，所以才会弹出不是全屏的界面。
typedef NS_ENUM(NSInteger, UIModalPresentationStyle) {
UIModalPresentationFullScreen = 0,
UIModalPresentationPageSheet API_AVAILABLE(ios(3.2)) API_UNAVAILABLE(tvos),
UIModalPresentationFormSheet API_AVAILABLE(ios(3.2)) API_UNAVAILABLE(tvos),
UIModalPresentationCurrentContext API_AVAILABLE(ios(3.2)),
UIModalPresentationCustom API_AVAILABLE(ios(7.0)),
UIModalPresentationOverFullScreen API_AVAILABLE(ios(8.0)),
UIModalPresentationOverCurrentContext API_AVAILABLE(ios(8.0)),
UIModalPresentationPopover API_AVAILABLE(ios(8.0)) API_UNAVAILABLE(tvos),
UIModalPresentationBlurOverFullScreen API_AVAILABLE(tvos(11.0)) API_UNAVAILABLE(ios) API_UNAVAILABLE(watchos),
UIModalPresentationNone API_AVAILABLE(ios(7.0)) = -1,
UIModalPresentationAutomatic API_AVAILABLE(ios(13.0)) = -2,
};
注意：presentViewController默认的UIModalPresentationAutomatic推出新的VC的时候，原VC不会调用viewWillDisappear与viewDidDisappear方法；退出新VC时，原VC不会调用viewWillAppear与viewDidAppear方法。
eg：vcA presentViewController vcB
vcA->vcB：vcA不会调用viewWillDisappear与viewDidDisappear方法；
vcB->vcA：vcA不会调用viewWillAppear与viewDidAppear方法；
如果需要vcA 调用 调用viewWillDisappear与viewDidDisappear 修改modalPresentationStylew为UIModalPresentationFullScreen；