Imitate Facebook hide/show expanding/contracting N

问题:

In the new iOS7 Facebook iPhone app, when the user scrolls up the navigationBar gradually hides itself to a point where it completely vanishes. Then when the user scrolls down the navigationBar gradually shows itself.

How would you implement this behavior yourself? I am aware of the following solution but it disappears right away and it isn\'t tied to the speed of the user\'s scroll gesture at all.

[navigationController setNavigationBarHidden: YES animated:YES];

I hope this isn\'t a duplicate as I\'m not sure how best to describe the \"expanding/contracting\" behavior.

回答1:

The solution given by @peerless is a great start, but it only kicks off an animation whenever dragging begins, without considering the speed of the scroll. This results in a choppier experience than you get in the Facebook app. To match Facebook\'s behavior, we need to:

• hide/show the navbar at a rate that is proportional to the rate of the drag
• kick off an animation to completely hide the bar if scrolling stops when the bar is partially hidden
• fade the navbar\'s items as the bar shrinks.

First, you\'ll need the following property:

@property (nonatomic) CGFloat previousScrollViewYOffset;

And here are the UIScrollViewDelegate methods:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGRect frame = self.navigationController.navigationBar.frame;
    CGFloat size = frame.size.height - 21;
    CGFloat framePercentageHidden = ((20 - frame.origin.y) / (frame.size.height - 1));
    CGFloat scrollOffset = scrollView.contentOffset.y;
    CGFloat scrollDiff = scrollOffset - self.previousScrollViewYOffset;
    CGFloat scrollHeight = scrollView.frame.size.height;
    CGFloat scrollContentSizeHeight = scrollView.contentSize.height + scrollView.contentInset.bottom;

    if (scrollOffset <= -scrollView.contentInset.top) {
        frame.origin.y = 20;
    } else if ((scrollOffset + scrollHeight) >= scrollContentSizeHeight) {
        frame.origin.y = -size;
    } else {
        frame.origin.y = MIN(20, MAX(-size, frame.origin.y - scrollDiff));
    }

    [self.navigationController.navigationBar setFrame:frame];
    [self updateBarButtonItems:(1 - framePercentageHidden)];
    self.previousScrollViewYOffset = scrollOffset;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    [self stoppedScrolling];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView 
                  willDecelerate:(BOOL)decelerate
{
    if (!decelerate) {
        [self stoppedScrolling];
    }
}

You\'ll also need these helper methods:

- (void)stoppedScrolling
{
    CGRect frame = self.navigationController.navigationBar.frame;
    if (frame.origin.y < 20) {
        [self animateNavBarTo:-(frame.size.height - 21)];
    }
}

- (void)updateBarButtonItems:(CGFloat)alpha
{
    [self.navigationItem.leftBarButtonItems enumerateObjectsUsingBlock:^(UIBarButtonItem* item, NSUInteger i, BOOL *stop) {
        item.customView.alpha = alpha;
    }];
    [self.navigationItem.rightBarButtonItems enumerateObjectsUsingBlock:^(UIBarButtonItem* item, NSUInteger i, BOOL *stop) {
        item.customView.alpha = alpha;
    }];
    self.navigationItem.titleView.alpha = alpha;
    self.navigationController.navigationBar.tintColor = [self.navigationController.navigationBar.tintColor colorWithAlphaComponent:alpha];
}

- (void)animateNavBarTo:(CGFloat)y
{
    [UIView animateWithDuration:0.2 animations:^{
        CGRect frame = self.navigationController.navigationBar.frame;
        CGFloat alpha = (frame.origin.y >= y ? 0 : 1);
        frame.origin.y = y;
        [self.navigationController.navigationBar setFrame:frame];
        [self updateBarButtonItems:alpha];
    }];
}

For a slightly different behavior, replace the line that re-positions the bar when scrolling (the else block in scrollViewDidScroll) with this one:

frame.origin.y = MIN(20, 
                     MAX(-size, frame.origin.y - 
                               (frame.size.height * (scrollDiff / scrollHeight))));

This positions the bar based on the last scroll percentage, instead of an absolute amount, which results in a slower fade. The original behavior is more Facebook-like, but I like this one, too.

Note: This solution is iOS 7+ only. Be sure to add the necessary checks if you\'re supporting older versions of iOS.

回答2:

EDIT: Only for iOS 8 and above.

You can try use

self.navigationController.hidesBarsOnSwipe = YES;

Works for me.

If your coding in swift you have to use this way (from https://stackoverflow.com/a/27662702/2283308)

navigationController?.hidesBarsOnSwipe = true

回答3:

Here is one more implementation: TLYShyNavBar v1.0.0 released!

I decided to make my own after trying the solutions provided, and to me, they were either performing poorly, had a a high barrier of entry and boiler plate code, or lacked the extension view beneath the navbar. To use this component, all you have to do is:

self.shyNavBarManager.scrollView = self.scrollView;

Oh, and it is battle tested in our own app.

回答4:

You can have a look at my GTScrollNavigationBar. I have subclassed UINavigationBar to make it scroll based on the scrolling of a UIScrollView.

Note: If you have an OPAQUE navigation bar, the scrollview must EXPAND as the navigation bar gets HIDDEN. This is exactly what GTScrollNavigationBar does. (Just as in for example Safari on iOS.)

回答5:

iOS8 includes properties to get the navigation bar hiding for free. There is a WWDC video that demonstrates it, search for \"View Controller Advancements in iOS 8\".

Example:

class QuotesTableViewController: UITableViewController {

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    navigationController?.hidesBarsOnSwipe = true
}

}

Other properties:

class UINavigationController : UIViewController {

    //... truncated

    /// When the keyboard appears, the navigation controller\'s navigationBar toolbar will be hidden. The bars will remain hidden when the keyboard dismisses, but a tap in the content area will show them.
    @availability(iOS, introduced=8.0)
    var hidesBarsWhenKeyboardAppears: Bool
    /// When the user swipes, the navigation controller\'s navigationBar & toolbar will be hidden (on a swipe up) or shown (on a swipe down). The toolbar only participates if it has items.
    @availability(iOS, introduced=8.0)
    var hidesBarsOnSwipe: Bool
    /// The gesture recognizer that triggers if the bars will hide or show due to a swipe. Do not change the delegate or attempt to replace this gesture by overriding this method.
    @availability(iOS, introduced=8.0)
    var barHideOnSwipeGestureRecognizer: UIPanGestureRecognizer { get }
    /// When the UINavigationController\'s vertical size class is compact, hide the UINavigationBar and UIToolbar. Unhandled taps in the regions that would normally be occupied by these bars will reveal the bars.
    @availability(iOS, introduced=8.0)
    var hidesBarsWhenVerticallyCompact: Bool
    /// When the user taps, the navigation controller\'s navigationBar & toolbar will be hidden or shown, depending on the hidden state of the navigationBar. The toolbar will only be shown if it has items to display.
    @availability(iOS, introduced=8.0)
    var hidesBarsOnTap: Bool
    /// The gesture recognizer used to recognize if the bars will hide or show due to a tap in content. Do not change the delegate or attempt to replace this gesture by overriding this method.
    @availability(iOS, introduced=8.0)
    unowned(unsafe) var barHideOnTapGestureRecognizer: UITapGestureRecognizer { get }
}

Found via http://natashatherobot.com/navigation-bar-interactions-ios8/

回答6:

I have some kind of a quick and dirty solution for that. Haven\'t made any in-depth testing but here\'s the idea:

That property will keep all the items in the navbar for my UITableViewController class

@property (strong, nonatomic) NSArray *navBarItems;

In the same UITableViewController class I have:

-(void)scrollViewDidScrollToTop:(UIScrollView *)scrollView
{
    if([[[UIDevice currentDevice] systemVersion] floatValue] < 7.0f){
        return;
    }

    CGRect frame = self.navigationController.navigationBar.frame;
    frame.origin.y = 20;

    if(self.navBarItems.count > 0){
        [self.navigationController.navigationBar setItems:self.navBarItems];
    }

    [self.navigationController.navigationBar setFrame:frame];
}

-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    if([[[UIDevice currentDevice] systemVersion] floatValue] < 7.0f){
        return;
    }

    CGRect frame = self.navigationController.navigationBar.frame;
    CGFloat size = frame.size.height - 21;

    if([scrollView.panGestureRecognizer translationInView:self.view].y < 0)
    {
        frame.origin.y = -size;

        if(self.navigationController.navigationBar.items.count > 0){
            self.navBarItems = [self.navigationController.navigationBar.items copy];
            [self.navigationController.navigationBar setItems:nil];
        }
    }
    else if([scrollView.panGestureRecognizer translationInView:self.view].y > 0)
    {
        frame.origin.y = 20;

        if(self.navBarItems.count > 0){
            [self.navigationController.navigationBar setItems:self.navBarItems];
        }
    }

    [UIView beginAnimations:@\"toggleNavBar\" context:nil];
    [UIView setAnimationDuration:0.2];
    [self.navigationController.navigationBar setFrame:frame];
    [UIView commitAnimations];
}

That\'s only for ios >= 7, it\'s ugly I know but a quick way to achieve this. Any comments/suggestions are welcome :)

回答7:

This works for iOS 8 and above and ensures that the status bar still retains its background

self.navigationController.hidesBarsOnSwipe = YES;
CGRect statuBarFrame = [UIApplication sharedApplication].statusBarFrame;
UIView *statusbarBg = [[UIView alloc] initWithFrame:statuBarFrame];
statusbarBg.backgroundColor = [UIColor blackColor];
[self.navigationController.view addSubview:statusbarBg];

And if you want to show the nav bar when you tap on the status bar you can do this:

- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView {
     self.navigationController.navigationBarHidden = NO;
}

回答8:

Here is my implementation: SherginScrollableNavigationBar.

In my approach I am using KVO for observing UIScrollView\'s state, so there is no necessity to use a delegate (and you can use this delegate for whatever else you need).

回答9:

Please try this solution of mine and let me know why this ain\'t as good as the previous answers.

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    if (fabs(velocity.y) > 1)
        [self hideTopBar:(velocity.y > 0)];
}

- (void)hideTopBar:(BOOL)hide
{
    [self.navigationController setNavigationBarHidden:hide animated:YES];
    [[UIApplication sharedApplication] setStatusBarHidden:hide withAnimation:UIStatusBarAnimationSlide];
}

回答10:

One way that I’ve accomplished this is the following.

Register your view controller to be the UIScrollViewDelegate of your UITableView for example.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView;
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

From within de UIScrollViewDelegate methods you can get the new contentOffset and translate your UINavigationBar up or down accordingly.

Setting the alpha of the subviews can also be done based on some threshold values and factors you can set and compute.

Hope it helps!

回答11:

In addition to Iwburk\'s answer I added the following to fix the alpha issue on non custom navigation bars and to reset the navigation bar in the viewWillDisappear method:

- (void)updateBarButtonItems:(CGFloat)alpha
{
    for (UIView *view in self.navigationController.navigationBar.subviews) {
        NSString *className = NSStringFromClass([view class]);

        if ( ![className isEqualToString:@\"_UINavigationBarBackground\"] ) {
            view.alpha = alpha;
        }
    }
}

- (void)resetNavigationBar {
    CGRect frame = self.navigationController.navigationBar.frame;
    frame.origin.y = 20;
    [self.navigationController.navigationBar setFrame:frame];
    [self updateBarButtonItems:1.0f];
}

回答12:

I was looking for a solution that allowed for any style and any behavior. You\'ll notice that bar condensing behavior is different in many different apps. And of course, the way the bar looks is totally different between apps.

I created a solution for this issue with https://github.com/bryankeller/BLKFlexibleHeightBar/

You can definine your own behavior rules to control how and when the bar shrinks and grows, and you can define exactly how you want the bar\'s subviews to react to the bar condensing or growing.

Have a look at my project if you want a lot of flexibility to make whatever kind of header bar you can think up.

回答13:

I tried implementing GTScrollNavigationBar but my app required me to modify auto layout constraints. I decided to put an example of my implementation up on GitHub in case anyone else has to do this with auto layout. The other issue I had with most of the other implementations is that people don\'t set the bounds of the scroll view to avoid the parallax scrolling effect that you create while you scroll and adjust the size of the scrollview simultaneously.

Check out JSCollapsingNavBarViewController if you need to do this with auto layout. I\'ve included two versions, one with the nav bar only and another with a sub-bar below the nav bar which collapses before collapsing the nav bar.

回答14:

I was trying to emulate this behavior in a situation where I needed a customized header sitting about a UITableView. I rolled my own \"navigation\" bar because this sits below a bunch of other stuff on the page and I wanted the section headers to follow the default \"docking\" behavior. I think I found a pretty clever and succinct way to adjust a UITableView/UIScrollView together with another object in a style similar to that seen in the Facebook/Instagram/Chrome/etc. apps.

In my .xib file, I have my components loaded into a freeform view: http://imgur.com/0z9yebJ (sorry, don\'t have the rep to inline images)

Notice that, in the left sidebar, the table is ordered behind the main header view. You can\'t tell from the screenshot, but it also has the same y position as the main header view. Since it extends out of sight, the contentInset property on the UITableView set to 76 (the height of the main header view).

To make the main header view slide up in unison with the UIScrollView, I use the UIScrollViewDelegate\'s scrollViewDidScroll methods to perform some calculations and change the UIScrollView\'s contentInset as well as the main header view\'s frame.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    UIEdgeInsets insets = scrollView.contentInset;
    //tableViewInsetDelta and tableViewOriginalInsetValue are NSInteger variables that I set to 0 and 76, respectively, in viewDidLoad
    tableViewInsetDelta = tableViewOriginalInsetValue + scrollView.contentOffset.y;
    insets.top = tableViewOriginalInsetValue - tableViewInsetDelta;

    if (scrollView.contentOffset.y > -76 && scrollView.contentOffset.y < 0) {
        [scrollView setContentInset:insets];
        self.pathTitleContainer.frame = CGRectMake(self.pathTitleContainer.frame.origin.x, 44 - tableViewInsetDelta, self.pathTitleContainer.frame.size.width, self.pathTitleContainer.frame.size.height);
    } else if (scrollView.contentOffset.y > 0) {
        insets.top = 0;
        [scrollView setContentInset:insets];
        self.pathTitleContainer.frame = CGRectMake(self.pathTitleContainer.frame.origin.x, -32, self.pathTitleContainer.frame.size.width, self.pathTitleContainer.frame.size.height);
    } else if (scrollView.contentOffset.y < -76) {
        insets.top = 76;
        [scrollView setContentInset:insets];
        self.pathTitleContainer.frame = CGRectMake(self.pathTitleContainer.frame.origin.x, 44, self.pathTitleContainer.frame.size.width, self.pathTitleContainer.frame.size.height);
    }
}

The first if statement does most of the heavy lifting, but I had to include the other two to handle situations where the user is dragging forcefully and the initial contentOffset values sent to scrollViewDidScroll are outside of the range of the first if statement.

Ultimately, this is working really well for me. I hate loading up my projects with a bunch of bloated subclasses. I can\'t speak to whether this is the best solution performance-wise (I\'ve always been hesitant to put any code in scrollViewDidScroll since it gets called all the time), but the code footprint is the smallest I\'ve seen in any solution for this problem and it doesn\'t involve nesting a UITableView in a UIScrollView (Apple advises against this in the documentation and touch events end up a bit funky on the UITableView). Hope this helps someone!

回答15:

HidingNavigationBar a great project that hides the Navigation Bar and the Tab Bar if you want.

HidingNavigationBar supports hiding/showing of the following view elements:

UINavigationBar

UINavigationBar and an extension UIView

UINavigationBar and a UIToolbar

UINavigationBar and a UITabBar

https://github.com/tristanhimmelman/HidingNavigationBar

回答16:

i tried it with this way, i hope it will help. just implement the code in delegate method and set to to the desired view/subview

-(void)scrollViewDidScroll:(UIScrollView *)scrollView{ 
            CGRect frame=self.view.frame;
            CGRect resultFrame=CGRectZero;
            if(scrollView.contentOffset.y==0 || scrollView.contentOffset.y<0){
                self.lastContentOffset=0;
                self.offset=0;
                resultFrame=CGRectMake(0, frame.size.height-(40-self.offset.intValue), frame.size.width, 40-self.offset.intValue);
    // Pass the resultFrame
                [self showHide:YES withFrame:resultFrame];
            }else if (self.lastContentOffset > scrollView.contentOffset.y){
                NSNumber *temp=[NSNumber numberWithDouble:self.lastContentOffset-scrollView.contentOffset.y];
                if(temp.intValue>40 || self.offset.intValue<temp.intValue){
                    self.offset=[NSNumber numberWithInt:0];
                    resultFrame=CGRectMake(0, frame.size.height-(40-self.offset.intValue), frame.size.width, 40-self.offset.intValue);
    // Pass the resultFrame
                    [self showHide:YES withFrame:resultFrame];
                }else{
                    if(temp.intValue>0){
                        self.offset=[NSNumber numberWithInt:self.offset.intValue-temp.intValue];
                        resultFrame=CGRectMake(0, frame.size.height-(40-self.offset.intValue), frame.size.width, 40-self.offset.intValue);
    // Pass the resultFrame
                        [self showHide:YES withFrame:resultFrame];
                    }
                }
            }else if (self.lastContentOffset < scrollView.contentOffset.y){
                NSNumber *temp=[NSNumber numberWithDouble:scrollView.contentOffset.y-self.lastContentOffset];
                if(self.offset.intValue>40 || (self.offset.intValue+temp.intValue)>40){
                    self.offset=[NSNumber numberWithInt:40];
    // Pass the resultFrame
                    [self showHide:NO withFrame:resultFrame];
                }else{
                    self.offset=[NSNumber numberWithInt:self.offset.intValue+temp.intValue];
                    resultFrame=CGRectMake(0, frame.size.height-(40-self.offset.intValue), frame.size.width, 40-self.offset.intValue);
    // Pass the resultFrame
                    [self showHide:YES withFrame:resultFrame];
                }
            }
            self.lastContentOffset = scrollView.contentOffset.y;

        }

-(void)showHide:(Boolean)boolView withFrame:(CGRect)frame{
               if(showSRPFilter){
                        //Assign value of \"frame\"to any view on which you wan to to perform animation
                }else{
                       //Assign value of \"frame\"to any view on which you wan to to perform animation
                }
        }

回答17:

An extension of @Iwburk \'s answer... Instead of changing the origin of the navigation bar, I needed to expand/shrink the size of the navigation bar.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGRect frame = self.previousRect; // a property set in the init method to hold the initial size of the uinavigationbar
    CGFloat size = frame.size.height;
    CGFloat framePercentageHidden = ((MINIMUMNAVBARHEIGHT - frame.origin.y) / (frame.size.height - 1));
    CGFloat scrollOffset = scrollView.contentOffset.y;
    CGFloat scrollDiff = scrollOffset - self.previousScrollViewYOffset;
    CGFloat scrollHeight = scrollView.frame.size.height;
    CGFloat scrollContentSizeHeight = scrollView.contentSize.height + scrollView.contentInset.bottom;

    if (scrollOffset <= -scrollView.contentInset.top) {
        frame.origin.y = -MINIMUMNAVBARHEIGHT;
    } else if ((scrollOffset + scrollHeight) >= scrollContentSizeHeight) {
        frame.origin.y = -size;
    } else {
        frame.origin.y = MIN(-MINIMUMNAVBARHEIGHT, MAX(-size, frame.origin.y - scrollDiff));
    }

    self.previousRect = CGRectMake(0, frame.origin.y, self.jsExtendedBarView.frame.size.width, 155);
    self.layoutConstraintExtendedViewHeight.constant = MAXIMUMNAVBARHEIGHT + frame.origin.y + MINIMUMNAVBARHEIGHT;
    [self updateBarButtonItems:(1 - framePercentageHidden)];
    self.previousScrollViewYOffset = scrollOffset;
}

It doesn\'t work with the stoppedScrolling method yet, ill post an update when I have it

回答18:

All of these approaches seem overly complicated... So naturally, I built my own:

class ViewController: UIViewController, UIScrollViewDelegate {
    var originalNavbarHeight:CGFloat = 0.0
    var minimumNavbarHeight:CGFloat = 0
    weak var scrollView:UIScrollView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        // setup delegates 
        scrollView.delegate = self
        // save the original nav bar height
        originalNavbarHeight = navigationController!.navigationBar.height
    }


    func scrollViewDidScroll(scrollView: UIScrollView) {
        // will relayout subviews
        view.setNeedsLayout() // calls viewDidLayoutSubviews
    }

    override func viewDidLayoutSubviews() {
        var percentageScrolled = min(scrollView.contentOffset.y / originalNavbarHeight, 1)
        navigationController?.navigationBar.height = min(max((1 - percentageScrolled) * originalNavbarHeight, minimumNavbarHeight), originalNavbarHeight)
        // re-position and scale scrollview
        scrollView.y = navigationController!.navigationBar.height + UIApplication.sharedApplication().statusBarFrame.height
        scrollView.height = view.height - scrollView.y
    }

    override func viewWillDisappear(animated: Bool) {
        navigationController?.navigationBar.height = originalNavbarHeight
    }

}

回答19:

I found all answers given in Objective-C. This is my answer in Swift 3. This is very generic code and can be used directly. It works with both UIScrollView and UITableView.

var lastContentOffset: CGPoint? = nil
var maxMinus: CGFloat           = -24.0
var maxPlus: CGFloat            = 20.0
var initial: CGFloat            = 0.0

override func viewDidLoad() {
    super.viewDidLoad()

    self.title = \"Alarm Details\"
    self.lastContentOffset = self.alarmDetailsTableView.contentOffset
    initial = maxPlus
}

func scrollViewDidScroll(_ scrollView: UIScrollView)
{
    var navigationBarFrame: CGRect   = self.navigationController!.navigationBar.frame
    let currentOffset = scrollView.contentOffset

    if (currentOffset.y > (self.lastContentOffset?.y)!) {
        if currentOffset.y > 0 {
            initial = initial - fabs(CGFloat(currentOffset.y - self.lastContentOffset!.y))
        }
        else if scrollView.contentSize.height < scrollView.frame.size.height {
            initial = initial + fabs(CGFloat(currentOffset.y - self.lastContentOffset!.y))
        }
    }
    else {
        if currentOffset.y < scrollView.contentSize.height - scrollView.frame.size.height {
            initial = initial + fabs(CGFloat(currentOffset.y - self.lastContentOffset!.y))
        }
        else if scrollView.contentSize.height < scrollView.frame.size.height && initial < maxPlus {
            initial = initial - fabs(CGFloat(currentOffset.y - self.lastContentOffset!.y))
        }
    }

    initial = (initial <= maxMinus) ? maxMinus : initial
    initial = (initial >= maxPlus) ? maxPlus : initial

    navigationBarFrame.origin.y = initial

    self.navigationController!.navigationBar.frame = navigationBarFrame
    scrollView.frame = CGRect(x: 0.0, y: initial + navigationBarFrame.size.height , width: navigationBarFrame.size.width, height: self.view.frame.size.height - (initial + navigationBarFrame.size.height))

    let framePercentageHidden: CGFloat              = ((20 - navigationBarFrame.origin.y) / (navigationBarFrame.size.height));
    self.lastContentOffset                          = currentOffset;
    self.updateBarButtonItems(alpha: 1 - framePercentageHidden)
}

func updateBarButtonItems(alpha: CGFloat)
{
    self.navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.darkGray.withAlphaComponent(alpha)]
    self.navigationController?.navigationBar.isUserInteractionEnabled = (alpha < 1) ? false: true

    guard (self.navigationItem.leftBarButtonItems?.count) != nil else { return }

    for (_, value) in self.navigationItem.leftBarButtonItems!.enumerated() {
        value.customView?.alpha = alpha
    }

    guard (self.navigationItem.rightBarButtonItems?.count) != nil else { return }

    for (_, value) in (self.navigationItem.rightBarButtonItems?.enumerated())! {
        value.customView?.alpha = alpha
    }
}

The logic of setting alpha to navigation items is copied from @WayneBurkett answer and rewritten in Swift 3.