iPhone: How to switch tabs with an animation?

问题

I'm switching tabs programmatically in a tab bar driven application using UITabBarController.selectedIndex. The problem I'm trying to solve is how to animate the transition between the views. ie.. from the view of the current tab to the view of the selected tab.

The first thought was to make use of the UITabBarControllerDelegate, but it appears that this is not called when programmatically switching tabs. I'm now considering the UITabBarDelegate.didSelectItem: as a possible hook to set a transition animation.

Has anyone manageged to animate the transitions? How did you go about it?

回答

After much research I came up with two working solutions. Both of these worked and did the animation between tabs.

Solution 1: transition from view (simple)

This is the easiest and makes use of a predefined UIView transition method. With this solution we don't need to manage the views because the method does the work for us.

// 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;
                    }
                }];

---

Solution 2: scroll (more complex)

A more complex solution, but gives you more control of the animation. In this example we get the views to slide on and off. With this one we need to manage the views ourselves.

// 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;                
                     }
                 }];