- (void)barBtnItemSwitchViews_Clicked:(id)sender {
    UIBarButtonItem *barButton = (UIBarButtonItem *)sender;
    barButton.enabled = NO;
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:0.8];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
    if(!self.yellowVC.view.superview) {
    	[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:innerView cache:YES];
    	[yellowVC viewWillAppear:YES];
    	[blueVC viewWillDisappear:YES];
    	[blueVC.view removeFromSuperview];
    	self.blueVC = nil;
    	[innerView addSubview:yellowVC.view];
    } else if(!self.blueVC.view.superview) {
    	[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:innerView cache:YES];
    	[blueVC viewWillAppear:YES];
    	[yellowVC viewWillDisappear:YES];
    	[yellowVC.view removeFromSuperview];
    	self.yellowVC = nil;
    	[innerView addSubview:blueVC.view];
    }
    [UIView commitAnimations];
    [UIView setAnimationDidStopSelector:@selector(enableControl:)]; // How do I pass barButton??
}

- (void)enableControl:(UIControl *)control {
    control.enabled = YES;
}

- (void)barBtnItemSwitchViews_Clicked:(id)sender {
    UIBarButtonItem *barButton = (UIBarButtonItem *)sender;
    barButton.enabled = NO;
    [UIView beginAnimations:nil context:barButton];
    [UIView setAnimationDuration:0.8];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
    if(!self.yellowVC.view.superview) {
    	[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:innerView cache:YES];
    	[yellowVC viewWillAppear:YES];
    	[blueVC viewWillDisappear:YES];
    	[blueVC.view removeFromSuperview];
    	self.blueVC = nil;
    	[innerView addSubview:yellowVC.view];
    } else if(!self.blueVC.view.superview) {
    	[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:innerView cache:YES];
    	[blueVC viewWillAppear:YES];
    	[yellowVC viewWillDisappear:YES];
    	[yellowVC.view removeFromSuperview];
    	self.yellowVC = nil;
    	[innerView addSubview:blueVC.view];
    }
    [UIView setAnimationDidStopSelector:@selector(flipViewAnimationDidStop:finished:context:)];
    [UIView commitAnimations];
}

- (void)flipViewAnimationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
    UIBarButtonItem *barButton = (UIBarButtonItem *)context;
    barButton.enabled = NO;
    NSLog(@"Disabled");
}

NSInvocation *inv = [[NSInvocation alloc] init];
[inv setSelector:@selector(foo:bar:)];
[inv setArgument:123 atIndex:0];
[inv setArgument:456 atIndex:1];