about catransition - popup

Question

i used catransition to do the animation. i want to click a button and then my view layer popup from the bottom and cover the screen. then click the button again and my view layer should popdown to the bottom and dispeared. my code is under. the popup function works ok.but the popdown function did not work well. my view layer just dispeared did not show the popdown action.
can anybody tell me how to do? thanks a lot
#define HIDE_REG CGRectMake(0,372,0,0)
#define POPUP_REG CGRectMake(0,0,320,372)
- (void)viewDidLoad
{
[super viewDidLoad];
// Uncomment the following line to preserve selection between presentations.
// self.clearsSelectionOnViewWillAppear = NO;
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
[otherText setFrame:HIDE_REG];
isPopup = NO;
}
-(void)popup:(NSString *) content
{
CATransition *animation = [CATransition animation];
animation.delegate = self;
animation.duration = 0.5f;
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
animation.fillMode = kCAFillModeForwards;
animation.type = kCATransitionPush;
animation.subtype = kCATransitionFromRight;
[self.otherText.layer addAnimation:animation forKey:#"animation"];
[self.otherText setFrame:POPUP_REG];
}
-(void)popdown:(NSString *) content
{
CATransition *animation = [CATransition animation];
animation.delegate = self;
animation.duration = 0.5f;
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
animation.fillMode = kCAFillModeForwards;
animation.type = kCATransitionPush;
animation.subtype = kCATransitionFromLeft;
[self.otherText.layer addAnimation:animation forKey:#"animation"];
[self.otherText setFrame:HIDE_REG];
}