UITabBarController View Transition error

OKay I have been working on this problem for a while now, And It is well beyond my expertise thus why I am asking for help again.

I am trying to animate the transition for a tabbarbutton click to another view. I have declared in both viewController (ViewWillAppear) methods the code below

- (void)viewWillAppear:(BOOL)animated
{
    //TODO: Fix transition animation

    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:1.0];
    [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight
                           forView:self.view cache:YES];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
    [UIView commitAnimations];

    [super viewWillAppear:animated];  
}

FirstViewController to the right and SecondViewController to the left.

Now the problem is happening when the user loads the app for the first time, once everything loads up and the user clicks on the tabbarbutton to 开发者_开发百科go to the second view, it dose not flip.. but when you go back to the FirstView it animates then if you go to the second again it will animate this time round.. Dose anyone have any idea why this is happeneing? if you do your help would be greatly appreciated!

UPDATE:: I am trying to add a animation into viewDidLoad, however there is already an animation for an opening sequence I am loading straight away.

[super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    //-- Start Opening Animation ------->
    CGRect vaultTopFrame = vaultTop.frame;
    vaultTopFrame.origin.y = -vaultTopFrame.size.height;

    CGRect vaultBottomFrame = vaultBottom.frame;
    vaultBottomFrame.origin.y = self.view.bounds.size.height;

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:2.5];
    [UIView setAnimationDelay:2.0];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];

    vaultTop.frame = vaultTopFrame;
    vaultBottom.frame = vaultBottomFrame;

    [self.view bringSubviewToFront:vaultTop];   //this should place this subview above any others on the same page
    [self.view bringSubviewToFront:vaultBottom]; //this should place this subview above any others on the same page

    [UIView  commitAnimations];

I think this might be messing things up for me what do you think?

You do not have animation when the app loads up. Set animation in viewDidLoad for animation when the view loads up and viewDidAppear will give you animations when the user makes transition after wards (every time the tab is clicked).

This may or may not be the problem, but you should call

[super viewWillAppear:animated];  

at the beginning of the method, before your animation code.