NINavigationBar.m

// NINavigationBar.h
@protocol ScheduleNavigationDelegate

- (NSString *)getScheduleScreenIdentifier;

@end

@interface NINavigationBarSchedule : UINavigationBar

@property (nonatomic, strong) id<ScheduleNavigationDelegate> scheduleDelegate;

@end

// NINavigationBar.m
@interface NINavigationBarSchedule ()

@property (nonatomic, strong) NIScheduleNavigationDropdown *dropDown;

@end

@implementation NINavigationBarSchedule

- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self addNavigationSlideDownGesture];
        [self makeSlideDownView];
    }
    return self;
}

- (void)addNavigationSlideDownGesture
{
    UITapGestureRecognizer *singleTap;
    singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(didTap:)];
    [singleTap setNumberOfTouchesRequired:1];
    [singleTap setEnabled:YES];
    [self addGestureRecognizer:singleTap];
}

- (void)makeSlideDownView
{
    CGRect frame = CGRectMake(0, 0, 320, 144);
    frame.origin.y = CGRectGetMaxY(self.frame) - frame.size.height + 20;
    
    self.dropDown = [[NIScheduleNavigationDropdown alloc] initWithFrame:frame];
}

- (void)didTap:(id)sender
{
    // find the subclassed UINavigationItem that has all the custom styles applied to it
    NINavigationItemSchedule *scheduleItem = nil;
    for (UINavigationItem *item in self.items) {
        if ([item isKindOfClass:[NINavigationItemSchedule class]]) {
            scheduleItem = (NINavigationItemSchedule *)item;
            break;
        }
    }
    
    // show or hide the dropdown
    CGFloat slideTime = 0.25f;
    if (self.dropDown.hidden) {
        [self slideNavigationMenuDownWithDuration:slideTime forNavigationItem:scheduleItem];
    } else {
        [self slideNavigationMenuUpWithDuration:slideTime forNavigationItem:scheduleItem];
    }
}

- (void)slideNavigationMenuDownWithDuration:(CGFloat)duration forNavigationItem:(NINavigationItemSchedule *)scheduleItem
{
    // flip the chevron arrow
    scheduleItem.titleView = [scheduleItem upChevronAttributedLabel];
    
    self.dropDown.hidden = NO;
    [self.superview insertSubview:self.dropDown belowSubview:self];
    [self.dropDown setHighlightedItem:[self.scheduleDelegate getScheduleScreenIdentifier]];
    [UIView animateWithDuration:duration animations:^{
        CGRect frame = self.dropDown.frame;
        frame.origin.y = CGRectGetMaxY(self.frame);
        self.dropDown.frame = frame;
    }];
}

- (void)slideNavigationMenuUpWithDuration:(CGFloat)duration forNavigationItem:(NINavigationItemSchedule *)scheduleItem
{
    // flip the chevron arrow
    scheduleItem.titleView = [scheduleItem downChevronAttributedLabel];
    
    [UIView animateWithDuration:duration animations:^{
        CGRect frame = CGRectMake(0, 0, 320, 144);
        frame.origin.y = CGRectGetMaxY(self.frame) - frame.size.height;
        self.dropDown.frame = frame;
    } completion:^(BOOL finished) {
        self.dropDown.hidden = YES;
    }];
}

@end