UIKIT_EXTERN NSString *const UIKeyboardWillChangeFrameNotification;
键盘可能因为改变输入法,切换成表情输入,切换成英文,那么frame可能会变高,变矮,不一定会发出下面这些通知,但是肯定会发上面的通知。
UIKIT_EXTERN?NSString *const UIKeyboardWillShowNotification;
UIKIT_EXTERN?NSString *const UIKeyboardDidShowNotification;
UIKIT_EXTERN?NSString *const UIKeyboardWillHideNotification;
UIKIT_EXTERN?NSString *const UIKeyboardDidHideNotification;
