UITabBar items jumping on back navigation on iOS 12.1

Question

I have an iOS app with UITabBarController on a master screen, navigating to a detail screen hiding the UITabBarController with setting hidesB

Answer 1

import UIKit

extension UITabBar{

open override func layoutSubviews() {
    super.layoutSubviews()
    if let UITabBarButtonClass = NSClassFromString("UITabBarButton") as? NSObject.Type{
        let subItems = self.subviews.filter({return $0.isKind(of: UITabBarButtonClass)})
        if subItems.count > 0{
            let tmpWidth = UIScreen.main.bounds.width / CGFloat(subItems.count)
            for (index,item) in subItems.enumerated(){
                item.frame = CGRect(x: CGFloat(index) * tmpWidth, y: 0, width: tmpWidth, height: item.bounds.height)
                }
            }
        }
    }

open override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
    if let view:UITabBar = super.hitTest(point, with: event) as? UITabBar{
        for item in view.subviews{
            if point.x >= item.frame.origin.x  && point.x <= item.frame.origin.x + item.frame.size.width{
                return item
                }
            }
        }
        return super.hitTest(point, with: event)
    }
}

Answer 2

there are two ways to fix this issue, Firstly, In your UITabBarController, set isTranslucent = false like:

[[UITabBar appearance] setTranslucent:NO];

sencondly, if the first solution does not fix your issur, try this way:

here is the Objective-C code

// .h
@interface CYLTabBar : UITabBar
@end 

// .m
#import "CYLTabBar.h"

CG_INLINE BOOL
OverrideImplementation(Class targetClass, SEL targetSelector, id (^implementationBlock)(Class originClass, SEL originCMD, IMP originIMP)) {
   Method originMethod = class_getInstanceMethod(targetClass, targetSelector);
   if (!originMethod) {
       return NO;
   }
   IMP originIMP = method_getImplementation(originMethod);
   method_setImplementation(originMethod, imp_implementationWithBlock(implementationBlock(targetClass, targetSelector, originIMP)));
   return YES;
}
@implementation CYLTabBar

+ (void)load {

   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
       if (@available(iOS 12.1, *)) {
           OverrideImplementation(NSClassFromString(@"UITabBarButton"), @selector(setFrame:), ^id(__unsafe_unretained Class originClass, SEL originCMD, IMP originIMP) {
               return ^(UIView *selfObject, CGRect firstArgv) {

                   if ([selfObject isKindOfClass:originClass]) {

                       if (!CGRectIsEmpty(selfObject.frame) && CGRectIsEmpty(firstArgv)) {
                           return;
                       }
                   }

                   // call super
                   void (*originSelectorIMP)(id, SEL, CGRect);
                   originSelectorIMP = (void (*)(id, SEL, CGRect))originIMP;
                   originSelectorIMP(selfObject, originCMD, firstArgv);
               };
           });
       }
   });
}
@end

More information:https://github.com/ChenYilong/CYLTabBarController/commit/2c741c8bffd47763ad2fca198202946a2a63c4fc

Answer 3

I was facing the exact same issue, where the app was architectured with one navigation controller per tab. The easiest non-hacky way that I found to fix this, was to place the UITabBarController inside a UINavigationController, and remove the individual UINavigationControllers.

Before:

                   -> UINavigationController -> UIViewController
                   -> UINavigationController -> UIViewController
UITabBarController -> UINavigationController -> UIViewController
                   -> UINavigationController -> UIViewController
                   -> UINavigationController -> UIViewController

After:

                                             -> UIViewController
                                             -> UIViewController
UINavigationController -> UITabBarController -> UIViewController
                                             -> UIViewController
                                             -> UIViewController

By using the outer UINavigationController, you don't need to hide the UITabBar when pushing a view controller onto the navigation stack.

Caveat:

The only issue I found so far, is that setting the title or right/left bar button items on each UIViewController does not have the same effect. To overcome this issue, I applied the changes via the UITabBarControllerDelegate when the visible UIViewController has changed.

func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
    guard let topItem = self.navigationController?.navigationBar.topItem else { return }
    precondition(self.navigationController == viewController.navigationController, "Navigation controllers do not match. The following changes might result in unexpected behaviour.")
    topItem.title = viewController.title
    topItem.titleView = viewController.navigationItem.titleView
    topItem.leftBarButtonItem = viewController.navigationItem.leftBarButtonItem
    topItem.rightBarButtonItem = viewController.navigationItem.rightBarButtonItem
}

Note that I have added a preconditionFailure to catch any case when the navigation architecture has been modified

Answer 4

In my case (iOS 12.1.4), I found that this weird glitchy behaviour was triggered by modals being presented with the .modalPresentationStyle = .fullScreen

After updating their presentationStyle to .overFullScreen, the glitch went away.

Answer 5

In your UITabBarController, set isTranslucent = false

Answer 6

Thanks for the idea of @ElonChan, I just changed the c inline function to OC static method, since I won't use this overrideImplementation too much. And also, this snippet was adjusted to iPhoneX now.

static CGFloat const kIPhoneXTabbarButtonErrorHeight = 33;
static CGFloat const kIPhoneXTabbarButtonHeight = 48;


@implementation FixedTabBar


typedef void(^NewTabBarButtonFrameSetter)(UIView *, CGRect);
typedef NewTabBarButtonFrameSetter (^ImpBlock)(Class originClass, SEL originCMD, IMP originIMP);


+ (BOOL)overrideImplementationWithTargetClass:(Class)targetClass targetSelector:(SEL)targetSelector implementBlock:(ImpBlock)implementationBlock {
    Method originMethod = class_getInstanceMethod(targetClass, targetSelector);
    if (!originMethod) {
        return NO;
    }
    IMP originIMP = method_getImplementation(originMethod);
    method_setImplementation(originMethod, imp_implementationWithBlock(implementationBlock(targetClass, targetSelector, originIMP)));
    return YES;
}


+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (@available(iOS 12.1, *)) {
            [self overrideImplementationWithTargetClass:NSClassFromString(@"UITabBarButton")
                                         targetSelector:@selector(setFrame:)
                                         implementBlock:^NewTabBarButtonFrameSetter(__unsafe_unretained Class originClass, SEL originCMD, IMP originIMP) {
                return ^(UIView *selfObject, CGRect firstArgv) {
                    if ([selfObject isKindOfClass:originClass]) {
                        if (!CGRectIsEmpty(selfObject.frame) && CGRectIsEmpty(firstArgv)) {
                            return;
                        }
                        if (firstArgv.size.height == kIPhoneXTabbarButtonErrorHeight) {
                            firstArgv.size.height = kIPhoneXTabbarButtonHeight;
                        }
                    }
                    void (*originSelectorIMP)(id, SEL, CGRect);
                    originSelectorIMP = (void (*)(id, SEL, CGRect))originIMP;
                    originSelectorIMP(selfObject, originCMD, firstArgv);
                };
            }];
        }
    });
}

@end