Pagination error scrollview - iphone

Question

I ahve a view controller that holds 4 images ,i implement the pagination for these images this is my code
- (void)viewDidLoad {
[super viewDidLoad];
[imageViewObj setImage:[UIImage imageNamed:#"hand1#2x"]];
NSTimer *ImgChangeTimer = [NSTimer scheduledTimerWithTimeInterval:2.0
target:self
selector:#selector(changeImage)
userInfo:nil
repeats:YES];
pageControlBeingUsed = NO;
NSArray *colors = [NSArray arrayWithObjects:[UIImage imageNamed:#"help3#2x"], [UIImage imageNamed:#"help4#2x"], [UIImage imageNamed:#"help2#2x"],[UIImage imageNamed:#"help1#2x"] ,nil];
for (int i = 0; i < colors.count; i++) {
CGRect frame;
frame.origin.x = self.scrollView.frame.size.width *i;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
UIImageView*subview = [[UIView alloc] initWithFrame:frame];
UIImage *imggg = [colors objectAtIndex:i];
[subview setBackgroundColor:[UIColor colorWithPatternImage:imggg]];
[self.scrollView addSubview:subview];
[self.scrollView addSubview:imageViewObj];
[subview release];
}
self.scrollView.contentSize = CGSizeMake(self.scrollView.frame.size.width * colors.count, self.scrollView.frame.size.height);
self.pageControl.currentPage = 0;
self.pageControl.numberOfPages = colors.count;
my need is i want to put a close button in the last image ,or the close button is hidden for first three-images and will unhidden when the user paging the last image.is there any way to do this?.
Thanks in advance.
EDIT
if (self.pageControl.currentPage == 0) {
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"df" message:#"okkkk" delegate:self cancelButtonTitle:#"ok" otherButtonTitles:nil, nil];
[alert show];
[alert release];
}
i put this in viewdidlod and i get the alertview
but when i put "4" instead of "0" i didnt get the alertview

Answer 1

Just try with below code, snippet :
NSInteger page;
page = (scrollView.contentOffset.x/scrollView.frame.size.width);
if (page == 3) {
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"df" message:#"okkkk" delegate:self cancelButtonTitle:#"ok" otherButtonTitles:nil, nil];
[alert show];
[alert release];
}