iOS 获取今天的0点时间和下一天的0点时间

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *now = [NSDate date];
NSDateComponents *components = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:now];
NSDate *startDate = [calendar dateFromComponents:components];
NSDate *endDate = [calendar dateByAddingUnit:NSCalendarUnitDay value:1 toDate:startDate options:0];