动画切换rootViewController

- (void)restoreRootViewController:(UIViewController *)rootViewController
{

typedef void (^Animation)(void);
UIWindow* window = self.window;

Animation animation = ^{
  BOOL oldState = [UIView areAnimationsEnabled];
  [UIView setAnimationsEnabled:NO];
  window.rootViewController = rootViewController;
  [UIView setAnimationsEnabled:oldState];
};

[UIView transitionWithView:window
      duration:0.5f
        options:UIViewAnimationOptionTransitionCrossDissolve
    animations:animation
    completion:nil];

}