要实现单击item转场动画，只需实现UITabBarDelegate下面的这个方法
该代理方法加入位置，为自定义的UITabBarController视图控制器中，如：
@interface BuyerTabbarCtrl : UITabBarController
- (void)viewDidLoad
{
[super viewDidLoad];
self.delegate = self;
}
- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item
{
CATransition *animation = [CATransition animation]; //创建CATransition对象
animation.duration = 0.77f; //设置运动时间
animation.type = @"rippleEffect"; //设置运动type
// animation.type = kCATransitionPush;
animation.subtype = kCATransitionFromLeft; //设置子类
animation.timingFunction = UIViewAnimationOptionCurveEaseInOut; //设置运动速度
[self.view.layer addAnimation:animation forKey:@"animation"];
}
