UITabBarItem Icon Animation

I have found a better solution to this problem. Adding custom image view is not a better approach because in iOS 10.0 and later on changing the orientation the icon frame & text position changed. You just need to set the class of UITabBarController & put the following code.

override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {

    let index = self.tabBar.items?.index(of: item)
    let subView = tabBar.subviews[index!+1].subviews.first as! UIImageView
    self.performSpringAnimation(imgView: subView)
}

//func to perform spring animation on imageview
func performSpringAnimation(imgView: UIImageView) {

    UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {

        imgView.transform = CGAffineTransform.init(scaleX: 1.4, y: 1.4)

        //reducing the size
        UIView.animate(withDuration: 0.5, delay: 0.2, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
            imgView.transform = CGAffineTransform.init(scaleX: 1, y: 1)
        }) { (flag) in
        }
    }) { (flag) in

    }
}  

Keep in mind that the order of the subviews in the UITabBar may be unordered so accessing the correct item from it using an index may not work correctly as Naresh answer suggested. Have a look at this post UITabBar subviews change order

The solution I found is to first filter and sort the views and then access it using the correct index of the tabBarItem.

func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {

    let orderedTabBarItemViews: [UIView] = {
        let interactionViews = tabBar.subviews.filter({ $0 is UIControl })
        return interactionViews.sorted(by: { $0.frame.minX < $1.frame.minX })
    }()

    guard
        let index = tabBar.items?.firstIndex(of: item),
        let subview = orderedTabBarItemViews[index].subviews.first
    else {
        return
    }

    performSpringAnimation(for: subview)
}

func performSpringAnimation(for view: UIView) {
    UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
        view.transform = CGAffineTransform(scaleX: 1.25, y: 1.25)
        UIView.animate(withDuration: 0.5, delay: 0.2, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
            view.transform = CGAffineTransform(scaleX: 1, y: 1)
        }, completion: nil)
    }, completion: nil)
}

You can animate tabbar icons by getting its view, then do whatever animation as you like for the UIView. Below is a simple example with scale transform, cheer!

func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem){
        var tabBarView: [UIView] = []

        for i in tabBar.subviews {
            if i.isKind(of: NSClassFromString("UITabBarButton")! ) {
                tabBarView.append(i)
            }
        }

        if !tabBarView.isEmpty {
            UIView.animate(withDuration: 0.15, animations: {
                tabBarView[item.tag].transform = CGAffineTransform(scaleX: 1.2, y: 1.2)
            }, completion: { _ in
                UIView.animate(withDuration: 0.15) {
                    tabBarView[item.tag].transform = CGAffineTransform.identity
                }
            })
        }
    }

ps: please assign tag for each UITabBarItem in order

Index of UIImageView in subviews is not guaranteed as fist.

The index of UIImageView is not guaranteed as fist in related subviews.

So it is better to access it via class type, and also check for index out of bounds.

override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
    guard let idx = tabBar.items?.firstIndex(of: item),
        tabBar.subviews.count > idx + 1,
        let imageView = tabBar.subviews[idx + 1].subviews.compactMap({ $0 as? UIImageView }).first else {
        return
    }
    
    imageView.layer.add(bounceAnimation, forKey: nil)
}

This is a sample basic bounce animation for that using CAKeyframeAnimation:

private var bounceAnimation: CAKeyframeAnimation = {
    let bounceAnimation = CAKeyframeAnimation(keyPath: "transform.scale")
    bounceAnimation.values = [1.0, 1.3, 0.9, 1.0]
    bounceAnimation.duration = TimeInterval(0.3)
    bounceAnimation.calculationMode = CAAnimationCalculationMode.cubic
    return bounceAnimation
}()

Simple way to animate tab bar item in objective c

In your tabbar controller class

    - (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item
    {
        UIVisualEffectView *viv = tabBar.subviews[item.tag].subviews.firstObject;
        UIImageView *img = viv.contentView.subviews.firstObject;
       // If UIImageView not get use this code
       // UIImageView *img  = tabBar.subviews[item.tag].subviews.lastObject;


        [self shakeAnimation:img];
      //[self bounceAnimation:img];

    }



- (void)shakeAnimation:(UIImageView *)img
{
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"position"];
    [animation setDuration:0.05];
    [animation setRepeatCount:2];
    [animation setAutoreverses:YES];
    [animation setFromValue:[NSValue valueWithCGPoint: CGPointMake([img center].x - 10.0f, [img center].y)]];
    [animation setToValue:[NSValue valueWithCGPoint: CGPointMake([img center].x + 10.0f, [img center].y)]];
    [[img layer] addAnimation:animation forKey:@"position"];
}


- (void)bounceAnimation:(UIImageView *)img
{
    img.transform = CGAffineTransformScale(CGAffineTransformIdentity, 0.001, 0.001);

    [UIView animateWithDuration:0.3/1.5 animations:^{
        img.transform = CGAffineTransformScale(CGAffineTransformIdentity, 1.1, 1.1);
    } completion:^(BOOL finished) {
        [UIView animateWithDuration:0.3/2 animations:^{
            img.transform = CGAffineTransformScale(CGAffineTransformIdentity, 0.9, 0.9);
        } completion:^(BOOL finished) {
            [UIView animateWithDuration:0.3/2 animations:^{
                img.transform = CGAffineTransformIdentity;
            }];
        }];
    }];
}