Estou alternando as guias programaticamente em um aplicativo conduzido por barra de guias usando UITabBarController.selectedIndex. O problema que estou tentando resolver é como animar a transição entre as visualizações. ou seja, da visualização da guia atual para a visualização da guia selecionada.

O primeiro pensamento foi fazer uso do UITabBarControllerDelegate, mas parece que ele não é chamado ao alternar entre guias programaticamente. Agora estou considerando UITabBarDelegate.didSelectItem: como um possível gancho para definir uma animação de transição.

Alguém conseguiu animar as transições? Se sim, como?

Atualização 04/2016: Justed queria atualizar isso para agradecer a todos por todos os votos. Observe também que isto foi escrito originalmente quando ... antes do ARC, antes das restrições, antes de ... muitas coisas! Portanto, leve isso em consideração ao decidir se usará essas técnicas. Pode haver abordagens mais modernas. Ah, e se você encontrar um. Adicione uma resposta para que todos possam ver. Obrigado.

Algum tempo depois ...

Depois de muita pesquisa, descobri duas soluções de trabalho. Ambos funcionaram e fizeram a animação entre as guias.

Solução 1: transição da visão (simples)

Este é o mais fácil e usa um método de transição UIView predefinido. Com esta solução, não precisamos gerenciar as visualizações porque o método faz o trabalho para nós.

// Get views. controllerIndex is passed in as the controller we want to go to. 
UIView * fromView = tabBarController.selectedViewController.view;
UIView * toView = [[tabBarController.viewControllers objectAtIndex:controllerIndex] view];

// Transition using a page curl.
[UIView transitionFromView:fromView 
                    toView:toView 
                  duration:0.5 
                   options:(controllerIndex > tabBarController.selectedIndex ? UIViewAnimationOptionTransitionCurlUp : UIViewAnimationOptionTransitionCurlDown)
                completion:^(BOOL finished) {
                    if (finished) {
                        tabBarController.selectedIndex = controllerIndex;
                    }
                }];

Solução 2: rolar (mais complexo)

Uma solução mais complexa, mas oferece mais controle da animação. Neste exemplo, obtemos as visualizações para ativar e desativar. Com este, precisamos gerenciar as visualizações nós mesmos.

// Get the views.
UIView * fromView = tabBarController.selectedViewController.view;
UIView * toView = [[tabBarController.viewControllers objectAtIndex:controllerIndex] view];

// Get the size of the view area.
CGRect viewSize = fromView.frame;
BOOL scrollRight = controllerIndex > tabBarController.selectedIndex;

// Add the to view to the tab bar view.
[fromView.superview addSubview:toView];

// Position it off screen.
toView.frame = CGRectMake((scrollRight ? 320 : -320), viewSize.origin.y, 320, viewSize.size.height);

[UIView animateWithDuration:0.3 
                 animations: ^{

                     // Animate the views on and off the screen. This will appear to slide.
                     fromView.frame =CGRectMake((scrollRight ? -320 : 320), viewSize.origin.y, 320, viewSize.size.height);
                     toView.frame =CGRectMake(0, viewSize.origin.y, 320, viewSize.size.height);
                 }

                 completion:^(BOOL finished) {
                     if (finished) {

                         // Remove the old view from the tabbar view.
                         [fromView removeFromSuperview];
                         tabBarController.selectedIndex = controllerIndex;                
                     }
                 }];

Esta solução em Swift:

extension TabViewController: UITabBarControllerDelegate {
      public func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {

           let fromView: UIView = tabBarController.selectedViewController!.view
           let toView  : UIView = viewController.view
           if fromView == toView {
                 return false
           }

           UIView.transitionFromView(fromView, toView: toView, duration: 0.3, options: UIViewAnimationOptions.TransitionCrossDissolve) { (finished:Bool) in

        }
        return true
   }
}

a seguir é minha tentativa de usar o formulário de código drekka no método delegado (UITabBarControllerDelegate)

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController {

    NSArray *tabViewControllers = tabBarController.viewControllers;
    UIView * fromView = tabBarController.selectedViewController.view;
    UIView * toView = viewController.view;
    if (fromView == toView)
        return false;
    NSUInteger fromIndex = [tabViewControllers indexOfObject:tabBarController.selectedViewController];
    NSUInteger toIndex = [tabViewControllers indexOfObject:viewController];

    [UIView transitionFromView:fromView
                        toView:toView
                      duration:0.3
                       options: toIndex > fromIndex ? UIViewAnimationOptionTransitionFlipFromLeft : UIViewAnimationOptionTransitionFlipFromRight
                    completion:^(BOOL finished) {
                        if (finished) {
                            tabBarController.selectedIndex = toIndex;
                        }
                    }];
    return true;
}

Minha solução para iOS7.0 ou superior.

Você pode especificar um controlador de animação personalizado no delegado da barra de guias.

Implemente um controlador de animação como este:

@interface TabSwitchAnimationController : NSObject <UIViewControllerAnimatedTransitioning>

@end

@implementation TabSwitchAnimationController

- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
{
    return 0.2;
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    UIViewController* fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController* toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIView* toView = toVC.view;
    UIView* fromView = fromVC.view;

    UIView* containerView = [transitionContext containerView];
    [containerView addSubview:toView];
    toView.frame = [transitionContext finalFrameForViewController:toVC];

    // Animate by fading
    toView.alpha = 0.0;
    [UIView animateWithDuration:[self transitionDuration:transitionContext]
                          delay:0.0
                        options:UIViewAnimationOptionCurveEaseOut | UIViewAnimationOptionAllowUserInteraction
                     animations:^{
                         toView.alpha = 1.0;
                     }
                     completion:^(BOOL finished) {
                         toView.alpha = 1.0;
                         [fromView removeFromSuperview];
                         [transitionContext completeTransition:YES];
                     }];
}

@end

Em seguida, use-o em seu UITabBarControllerDelegate:

- (id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
            animationControllerForTransitionFromViewController:(UIViewController *)fromVC
                                              toViewController:(UIViewController *)toVC
{
    return [[TabSwitchAnimationController alloc] init];
}

Em vez de usar tabBarController:shouldSelectViewController:é melhor implementartabBarController:animationControllerForTransitionFromViewController:toViewController:

TransitioningObject.swift

import UIKit

class TransitioningObject: NSObject, UIViewControllerAnimatedTransitioning {

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let fromView: UIView = transitionContext.viewForKey(UITransitionContextFromViewKey)!
        let toView: UIView = transitionContext.viewForKey(UITransitionContextToViewKey)!

        transitionContext.containerView().addSubview(fromView)
        transitionContext.containerView().addSubview(toView)

        UIView.transitionFromView(fromView, toView: toView, duration: transitionDuration(transitionContext), options: UIViewAnimationOptions.TransitionCrossDissolve) { finished in
            transitionContext.completeTransition(true)
        }
    }

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning) -> NSTimeInterval {
        return 0.25
    }
}

TabBarViewController.swift

import UIKit

    class TabBarViewController: UITabBarController, UITabBarControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        self.delegate = self
    }

    // MARK: - Tabbar delegate

    func tabBarController(tabBarController: UITabBarController, animationControllerForTransitionFromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return TransitioningObject()
    }
}

Eu acho que você pode facilmente conseguir transições para UITabBarControlelr usando CATransition; Isso também resolverá quaisquer efeitos colaterais do uso de transactionFromView: toView:

Use-o dentro de sua classe TabBarController personalizada estendida de UITabBarController.

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController (UIViewController*)viewController {

    CATransition *animation = [CATransition animation];
    [animation setType:kCATransitionFade];
    [animation setDuration:0.25];
    [animation setTimingFunction:[CAMediaTimingFunction functionWithName:
                              kCAMediaTimingFunctionEaseIn]];
    [self.view.window.layer addAnimation:animation forKey:@"fadeTransition"];
}

Espero que isto ajude :)

Escrevi um post depois de tentar as várias respostas aqui.

O código está em Swift e você pode alterar programaticamente a guia com animação chamando animateToTab.

func animateToTab(toIndex: Int) {
    let tabViewControllers = viewControllers!
    let fromView = selectedViewController!.view
    let toView = tabViewControllers[toIndex].view    
    let fromIndex = tabViewControllers.indexOf(selectedViewController!)

    guard fromIndex != toIndex else {return}

    // Add the toView to the tab bar view
    fromView.superview!.addSubview(toView)

    // Position toView off screen (to the left/right of fromView)
    let screenWidth = UIScreen.mainScreen().bounds.size.width;
    let scrollRight = toIndex > fromIndex;
    let offset = (scrollRight ? screenWidth : -screenWidth)
    toView.center = CGPoint(x: fromView.center.x + offset, y: toView.center.y)

    // Disable interaction during animation
    view.userInteractionEnabled = false

    UIView.animateWithDuration(0.5, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: {

            // Slide the views by -offset
            fromView.center = CGPoint(x: fromView.center.x - offset, y: fromView.center.y);
            toView.center   = CGPoint(x: toView.center.x - offset, y: toView.center.y);

        }, completion: { finished in

            // Remove the old view from the tabbar view.
            fromView.removeFromSuperview()
            self.selectedIndex = toIndex
            self.view.userInteractionEnabled = true
        })
}

Se você quiser que todas as alterações de guia tenham a animação, conecte-a UITabBarControllerDelegatecomo esta:

func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
    let tabViewControllers = tabBarController.viewControllers!
    guard let toIndex = tabViewControllers.indexOf(viewController) else {
        return false
    }

    // Our method
    animateToTab(toIndex)

    return true
}

Minha solução em Swift:

Crie uma classe TabBar personalizada e configure-a em seu storyboard TabBar

class MainTabBarController: UITabBarController, UITabBarControllerDelegate {

override func viewDidLoad() {
    super.viewDidLoad()
    self.delegate = self
    // Do any additional setup after loading the view.
}

func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {


    let tabViewControllers = tabBarController.viewControllers!
    let fromView = tabBarController.selectedViewController!.view
    let toView = viewController.view

    if (fromView == toView) {
        return false
    }

    let fromIndex = tabViewControllers.indexOf(tabBarController.selectedViewController!)
    let toIndex = tabViewControllers.indexOf(viewController)

    let offScreenRight = CGAffineTransformMakeTranslation(toView.frame.width, 0)
    let offScreenLeft = CGAffineTransformMakeTranslation(-toView.frame.width, 0)

    // start the toView to the right of the screen


    if (toIndex < fromIndex) {
        toView.transform = offScreenLeft
        fromView.transform = offScreenRight
    } else {
        toView.transform = offScreenRight
        fromView.transform = offScreenLeft
    }

    fromView.tag = 124
    toView.addSubview(fromView)

    self.view.userInteractionEnabled = false
    UIView.animateWithDuration(0.5, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: {

        toView.transform = CGAffineTransformIdentity

        }, completion: { finished in

            let subViews = toView.subviews
            for subview in subViews{
                if (subview.tag == 124) {
                    subview.removeFromSuperview()
                }
            }
            tabBarController.selectedIndex = toIndex!
            self.view.userInteractionEnabled = true

    })

    return true
 }

}

Usei a solução de @Mofumofu e atualizei para Swift 1.2 e também implementei uma animação para cima / para baixo. Ou seja, o novo ViewController surge e empurra o antigo para cima se o índice do novo viewcontroller for maior que o antigo. Caso contrário, a direção é para baixo.

class TabScrollPageAnimationController: NSObject, UIViewControllerAnimatedTransitioning {

    let tabBarController: UITabBarController

    init(tabBarController: UITabBarController) {
        self.tabBarController = tabBarController
    }

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning) -> NSTimeInterval {
        return 0.5
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        if let fromVC = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey),
            let toVC = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey) {
                let fromView = fromVC.view
                let toView = toVC.view

                let containerView = transitionContext.containerView()

                var directionUpwardMultiplier: CGFloat = 1.0
                if let vcs = tabBarController.viewControllers as? [UIViewController],
                    let fIndex = find(vcs, fromVC),
                    let tIndex = find(vcs, toVC) {
                        directionUpwardMultiplier = (fIndex < tIndex) ? +1.0 : -1.0
                }

                containerView.clipsToBounds = false
                containerView.addSubview(toView)

                var fromViewEndFrame = fromView.frame
                fromViewEndFrame.origin.y -= (containerView.frame.height * directionUpwardMultiplier)

                let toViewEndFrame = transitionContext.finalFrameForViewController(toVC)
                var toViewStartFrame = toViewEndFrame
                toViewStartFrame.origin.y += (containerView.frame.height * directionUpwardMultiplier)
                toView.frame = toViewStartFrame

                toView.alpha = 0.0
                UIView.animateWithDuration(transitionDuration(transitionContext), delay: 0.0, usingSpringWithDamping: 1.0, initialSpringVelocity: 0.0, options: UIViewAnimationOptions.CurveEaseInOut, animations: { () -> Void in
                    toView.alpha = 1.0
                    toView.frame = toViewEndFrame
                    fromView.alpha = 0.0
                    fromView.frame = fromViewEndFrame
                }, completion: { (completed) -> Void in
                    toView.alpha = 1.0
                    fromView.removeFromSuperview()
                    transitionContext.completeTransition(completed)
                    containerView.clipsToBounds = true
                })

        }
    }

}

No Container ViewController:

extension XYViewController: UITabBarControllerDelegate {

    func tabBarController(tabBarController: UITabBarController, animationControllerForTransitionFromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return TabScrollPageAnimationController(tabBarController: tabBarController)
    }

}

Aqui está minha solução Swift 3:

Eu substituo o selectedIndex do meu UITabBarViewController assim:

override var selectedIndex: Int{
    get{
        return super.selectedIndex
    }
    set{
        animateToTab(toIndex: newValue)
        super.selectedIndex = newValue
    }
}

Então eu uso esta função que imita a animação push / pop nativa:

func animateToTab(toIndex: Int) {
    guard let tabViewControllers = viewControllers, tabViewControllers.count > toIndex, let fromViewController = selectedViewController, let fromIndex = tabViewControllers.index(of: fromViewController), fromIndex != toIndex else {return}

    view.isUserInteractionEnabled = false

    let toViewController = tabViewControllers[toIndex]
    let push = toIndex > fromIndex
    let bounds = UIScreen.main.bounds

    let offScreenCenter = CGPoint(x: fromViewController.view.center.x + bounds.width, y: toViewController.view.center.y)
    let partiallyOffCenter = CGPoint(x: fromViewController.view.center.x - bounds.width*0.25, y: fromViewController.view.center.y)

    if push{
        fromViewController.view.superview?.addSubview(toViewController.view)
        toViewController.view.center = offScreenCenter
    }else{
        fromViewController.view.superview?.insertSubview(toViewController.view, belowSubview: fromViewController.view)
        toViewController.view.center = partiallyOffCenter
    }

    UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: .curveEaseIn, animations: {
        toViewController.view.center   = fromViewController.view.center
        fromViewController.view.center = push ? partiallyOffCenter : offScreenCenter
    }, completion: { finished in
        fromViewController.view.removeFromSuperview()
        self.view.isUserInteractionEnabled = true
    })
}

Espero que ajude :)

uma correção para a animação nervosa ...

UIView * fromView = self.view.superview;

isso pode ser resolvido de duas maneiras

1 - Escreva isso no arquivo AppDelegate.m uma vez. Lembre-se de incluir UITabBarControllerDelegate usando <> depois de dois pontos (:) em seu AppDelegate.h

-(void)tabBarController:(UITabBarController *)tabBarControllerThis didSelectViewController:(UIViewController *)viewController
{
    [UIView transitionWithView:viewController.view
                      duration:0.1
                       options:UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionTransitionCrossDissolve
                    animations:^(void){
                    } completion:^(BOOL finished){
                        [UIView beginAnimations:@"animation" context:nil];
                        [UIView setAnimationDuration:0.7];
                        [UIView setAnimationBeginsFromCurrentState:YES];
                        [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft
                                               forView:viewController.view
                                                 cache:NO];
                        [UIView commitAnimations];
                    }];
}

2 - Escreva isso em cada um de seus arquivos ViewController.m

-(void)viewWillAppear:(BOOL)animated
{
    [UIView transitionWithView:self.view
                      duration:1.0
                       options:UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionTransitionCrossDissolve
                    animations:^(void){
                        [super viewWillAppear:YES];
                    } completion:^(BOOL finished){
                    }];
}

espero que esta ajuda ...!

Você pode animar dependendo do item tocado - Neste exemplo, invertemosFromLeft se o índice tocado for> do que o índice selecionado anteriormente e invertemosFromRight se o índice tocado for <do que o índice selecionado anteriormente. Este é o Swift 4: implemente o método UITabBarControllerDelegate

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {

    let fromView: UIView = tabBarController.selectedViewController!.view
    let toView: UIView = viewController.view

    if fromView == toView {
        return false
    }

    if let tappedIndex = tabBarController.viewControllers?.index(of: viewController) {
        if tappedIndex > tabBarController.selectedIndex {
            UIView.transition(from: fromView, to: toView, duration: 0.5, options: UIViewAnimationOptions.transitionFlipFromLeft, completion: nil)
        } else {
            UIView.transition(from: fromView, to: toView, duration: 0.5, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
        }
    }
    return true
}

A resposta de drekka é realmente ótima. Ajustei um pouco a transição de rolagem para que a animação parecesse mais com a animação push da Apple. Eu adicionei uma animação adicional após a conclusão da primeira animação para fazer com que o efeito deslizante pareça certo.

// Disable interaction during animation to avoids bugs.
self.tabBarController.view.userInteractionEnabled = NO;

// Get the views.
UIView * fromView = tabBarController.selectedViewController.view;
UIView * toView = [[tabBarController.viewControllers objectAtIndex:controllerIndex] view];

// Get the size of the view area.
CGRect viewSize = fromView.frame;
BOOL scrollRight = controllerIndex > tabBarController.selectedIndex;

// Add the to view to the tab bar view.
[fromView.superview addSubview:toView];
[fromView.superview addSubview:fromView];

self.tabBarController.selectedIndex = 0;

// Position it off screen.
toView.frame = CGRectMake((scrollRight ? (viewSize.size.width *.25) : -(viewSize.size.width * .25 )), viewSize.origin.y, viewSize.size.width, viewSize.size.height);

[UIView animateWithDuration:0.25 
             animations: ^{
                 // Animate the views on and off the screen.
                 [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
                 fromView.frame = CGRectMake(viewSize.size.width * .95, viewSize.origin.y, viewSize.size.width, viewSize.size.height);
                 toView.frame = CGRectMake((viewSize.origin.x * .90), viewSize.origin.y, viewSize.size.width, viewSize.size.height);
             }

             completion:^(BOOL finished) {
                 if (finished) {
                     // Being new animation.
                     [UIView animateWithDuration:0.2
                                          animations: ^{
                                              [UIView setAnimationCurve:UIViewAnimationCurveLinear];
                                              fromView.frame = CGRectMake(viewSize.size.width, viewSize.origin.y, viewSize.size.width, viewSize.size.height);
                                              toView.frame = CGRectMake((viewSize.origin.x), viewSize.origin.y, viewSize.size.width, viewSize.size.height);
                                          }
                                          completion:^(BOOL finished) {
                                              if (finished) {
                                                  // Remove the old view from the tabbar view.
                                                  [fromView removeFromSuperview];
                                                  // Restore interaction.
                                                  self.tabBarController.view.userInteractionEnabled = YES;
                                              }
                                          }];
                 }
             }];

Eu queria usar uma transição flip entre dois controladores de visualização filho em um toque de botão e consegui da seguinte maneira:

-(IBAction)flipViewControllers:(id)sender{
    NSUInteger index = self.selectedIndex;
    index++;
    if(index >= self.childViewControllers.count){
        index = 0;
    }

    self.selectedIndex = index;

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.75];
    [UIView setAnimationTransition:index % 2 ? UIViewAnimationTransitionFlipFromLeft : UIViewAnimationTransitionFlipFromRight
                           forView:self.view
                             cache:YES];
    [UIView commitAnimations];
}

Também defini a cor de fundo como preto, no meu caso fiz isso definindo o navigationController.view.backgroundColor, mas no seu caso pode ser o window.backgroundColor que pode ser facilmente definido no delegado do aplicativo.

Aqui está meu código de trabalho ( para 3 guias , não tentei mais !!) para animar as transições entre as guias. É baseado principalmente na solução de drekka, mas já implementado no método delegado da tabbar, então deve funcionar se você apenas copiar / colar. (Você nunca sabe!)

-(BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController {

// Important! We validate that the selected tab is not the current tab, to avoid misplacing views
if (tabBarController.selectedViewController == viewController) {
    return NO;
}

// Find the selected view's index
NSUInteger controllerIndex = 0;
for (UIViewController *vc in tabBarController.viewControllers) {
    if (vc == viewController) {
        controllerIndex = [tabBarController.viewControllers indexOfObject:vc];
    }
}

CGFloat screenWidth = SCREEN_SIZE.width;

// Note: We must invert the views according to the direction of the scrolling ( FROM Left TO right or FROM right TO left )
UIView * fromView = tabBarController.selectedViewController.view;
UIView * toView = viewController.view;

[fromView.superview addSubview:toView];
CGRect fromViewInitialFrame = fromView.frame;
CGRect fromViewNewframe = fromView.frame;

CGRect toViewInitialFrame = toView.frame;

if ( controllerIndex > tabBarController.selectedIndex ) {
// FROM left TO right ( tab0 to tab1 or tab2 )

    // The final frame for the current view. It will be displaced to the left
    fromViewNewframe.origin.x = -screenWidth;
    // The initial frame for the new view. It will be displaced to the left
    toViewInitialFrame.origin.x = screenWidth;
    toView.frame = toViewInitialFrame;

} else {
// FROM right TO left ( tab2 to tab1 or tab0 )

    // The final frame for the current view. It will be displaced to the right
    fromViewNewframe.origin.x = screenWidth;
    // The initial frame for the new view. It will be displaced to the right
    toViewInitialFrame.origin.x = -screenWidth;
    toView.frame = toViewInitialFrame;
}

[UIView animateWithDuration:0.2 animations:^{
    // The new view will be placed where the initial view was placed
    toView.frame = fromViewInitialFrame;
    // The initial view will be place outside the screen bounds
    fromView.frame = fromViewNewframe;

    tabBarController.selectedIndex = controllerIndex;

    // To prevent user interaction during the animation
    [[UIApplication sharedApplication] beginIgnoringInteractionEvents];

} completion:^(BOOL finished) {

    // Before removing the initial view, we adjust its frame to avoid visual lags
    fromView.frame = CGRectMake(0, 0, fromView.frame.size.width, fromView.frame.size.height);
    [fromView removeFromSuperview];

    [[UIApplication sharedApplication] endIgnoringInteractionEvents];
}];

return NO;

}

Isso funciona para mim no Swift 3:

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {

    if let fromView = tabBarController.selectedViewController?.view, let toView = viewController.view {

        if fromView == toView {
            return false
        }

        UIView.transition(from: fromView, to: toView, duration: 0.2, options: .transitionCrossDissolve) { (finished) in
        }
    }

    return true
}

@samwize Resposta traduzida para Swift 3 - 2 polegares para cima, cria um efeito de página da esquerda para a direita:

func animateToTab(toIndex: Int) {
        let tabViewControllers = viewControllers!
        let fromView = selectedViewController!.view
        let toView = tabViewControllers[toIndex].view
        let fromIndex = tabViewControllers.index(of: selectedViewController!)

        guard fromIndex != toIndex else {return}

        // Add the toView to the tab bar view
        fromView?.superview!.addSubview(toView!)

        // Position toView off screen (to the left/right of fromView)
        let screenWidth = screenSize.width
        let scrollRight = toIndex > fromIndex!
        let offset = (scrollRight ? screenWidth : -screenWidth)
        toView?.center = CGPoint(x: (fromView?.center.x)! + offset, y: (toView?.center.y)!)

        // Disable interaction during animation
        view.isUserInteractionEnabled = false

        UIView.animate(withDuration: 0.5, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: UIViewAnimationOptions.curveEaseOut, animations: {

            // Slide the views by -offset
            fromView?.center = CGPoint(x: (fromView?.center.x)! - offset, y: (fromView?.center.y)!);
            toView?.center   = CGPoint(x: (toView?.center.x)! - offset, y: (toView?.center.y)!);

        }, completion: { finished in

            // Remove the old view from the tabbar view.
            fromView?.removeFromSuperview()
            self.selectedIndex = toIndex
            self.view.isUserInteractionEnabled = true
        })
    }

Resposta de @samwize atualizada para Swift 5:

Se você quiser que todas as alterações da guia tenham a animação, use um UITabBarControllerDelegate e implemente este método:

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
  let tabViewControllers = tabBarController.viewControllers!
  guard let toIndex = tabViewControllers.indexOf(value:viewController) else {
    return false
  }
  animateToTab(toIndex: toIndex, fadeOutFromView: false, fadeInToView: false)
  return true
}

Altere programaticamente a guia com animação chamando animateToTab:

func animateToTab(toIndex: Int, fadeOutFromView: Bool, fadeInToView: Bool) {
  let tabViewControllers = viewControllers!
  let fromView = selectedViewController!.view
  let toView = tabViewControllers[toIndex].view
  let fromIndex = tabViewControllers.indexOf(value:selectedViewController!)
  guard fromIndex != toIndex else {return}

  // Add the toView to the tab bar view
  fromView!.superview!.addSubview(toView!)

  // Position toView off screen (to the left/right of fromView)
  let screenWidth = UIScreen.main.bounds.width
  let scrollRight = toIndex > fromIndex!;
  let offset = (scrollRight ? screenWidth : -screenWidth)
  toView!.center = CGPoint(x: fromView!.center.x + offset, y: toView!.center.y)

  // Disable interaction during animation
  view.isUserInteractionEnabled = false
  if fadeInToView {
    toView!.alpha = 0.1
  }

  UIView.animate(withDuration: 0.5, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: [.curveEaseOut], animations: {

    if fadeOutFromView {
      fromView!.alpha = 0.0
    }

    if fadeInToView {
      toView!.alpha = 1.0
    }

    // Slide the views by -offset
    fromView!.center = CGPoint(x: fromView!.center.x - offset, y: fromView!.center.y);
    toView!.center   = CGPoint(x: toView!.center.x - offset, y: toView!.center.y);

  }, completion: { finished in
    // Remove the old view from the tabbar view.
    fromView!.removeFromSuperview()
    self.selectedIndex = toIndex
    self.view.isUserInteractionEnabled = true
  })
}

Swift 4+

Seu UITabBarControllerDelegatemétodo deve ser assim,

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {

    animateToTab(toIndex: (tabBarController.viewControllers?.index(of: viewController))!)
    return true
}

E o método é,

func animateToTab(toIndex: Int) {
    let tabViewControllers = viewControllers!
    let fromView = selectedViewController!.view
    let toView = tabViewControllers[toIndex].view
    let fromIndex = tabViewControllers.index(of: selectedViewController!)

    guard fromIndex != toIndex else {return}

    // Add the toView to the tab bar view
    fromView!.superview!.addSubview(toView!)

    // Position toView off screen (to the left/right of fromView)
    let screenWidth = UIScreen.main.bounds.size.width;
    let scrollRight = toIndex > fromIndex!;
    let offset = (scrollRight ? screenWidth : -screenWidth)
    toView!.center = CGPoint(x: fromView!.center.x + offset, y: toView!.center.y)

    // Disable interaction during animation
    view.isUserInteractionEnabled = false

    UIView.animate(withDuration: 0.5, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 0, options: UIViewAnimationOptions.curveEaseOut, animations: {

        // Slide the views by -offset
        fromView!.center = CGPoint(x: fromView!.center.x - offset, y: fromView!.center.y);
        toView!.center   = CGPoint(x: toView!.center.x - offset, y: toView!.center.y);

    }, completion: { finished in

        // Remove the old view from the tabbar view.
        fromView!.removeFromSuperview()
        self.selectedIndex = toIndex
        self.view.isUserInteractionEnabled = true
    });

}