UITabBarControllerDelegate的方法未调用

Question

I create programmatically a UITabBarController with more than 5 tabs (exactly 8 child view controllers).

My purpose is custom transition animation for tab changing. I setup a delegate for the UITabbarController and implement the method:

- (nullable id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
            animationControllerForTransitionFromViewController:(UIViewController *)fromVC
                                              toViewController:(UIViewController *)toVC  

When I select a tab by sending:

[tabbarController setSelectedIndex: 6];

delegate's method is not called.

Delegate's method is called properly when I send

[tabbarController setSelectedIndex: 3]; 

for example, ie for a visible tab.

One more remark: if currently selected view controller is in visible range 0..3 and next view is out of the visible range 0..3 delegate's method is still called. In case when currently selected view controller is out of the visible range 0..3 and next view is out of the visible range 0..3 too delegate's method is not called. And I lose my custom transition animation. This is my problem.

I also tried to send

[tabbarController setSelectedViewController: someViewController];

instead of

[tabbarController setSelectedIndex: 6];

It doesn't work.

Answer 1

You have too many tabs to use selectedIndex , as your other tabs are probably in the moreNavigationController even if the moreNavigationController is not displayed on the screen - meaning they should return NSNotFound when using selectedIndex .

You should use selectedViewController instead, per iOS Docs

[tabbarController setSelectedViewController: yourIndexSixViewController];

Answer 2

I made tricky solution.

I collect all 8 view controllers in separated array. Call it controllers .

At start I fill tabbarController.viewcontrollers with first 5 items of controllers . Further there are 2 scenarios:

1. User wants to see a tab with index within range 0..4 . There is nothing to do because we already set appropriate viewcontrollers into tabbarController.viewcontrollers .

2. User wants to see a tab with index out of the range 0..4 . User wants to see the tab with index 6, for example. And currently selected tab has index 2, for example. In this case I select a number in range 0..4 which is unequal to currently selected tab index. For example 4. Further I replace tabbarController.viewcontrollers[4] with controllers[6] . After that I call

     [tabbarController setSelectedIndex: 4]; 

As result I see controllers[6] and delegate's method is called properly.