淡入淡出更换 rootViewController

- (void)restoreRootViewController:(UIViewController *)rootViewController

{

 typedef void (^Animation)(void);

 UIWindow* window = self.window;

  

 rootViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;

 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];

}