Detecting which UIView is being displayed within a pagingEnabled UIScrollView

I'm using the code from this tutorial to create a UIScrollView which allows scrolling through pages. Put in another way, the user can drag the screen to switch fro开发者_JS百科m one UIView to another. The code basically looks like this:

- (void)loadView {
[super loadView];
self.view.backgroundColor = [UIColor redColor];
UIScrollView *scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
scroll.pagingEnabled = YES;
NSInteger numberOfViews = 3;
for (int i = 0; i < numberOfViews; i++) {
CGFloat yOrigin = i * self.view.frame.size.width;
UIView *awesomeView = [[UIView alloc] initWithFrame:CGRectMake(yOrigin, 0, self.view.frame.size.width, self.view.frame.size.height)];
awesomeView.backgroundColor = [UIColor colorWithRed:0.5/i green:0.5 blue:0.5 alpha:1];
[scroll addSubview:awesomeView];
[awesomeView release];
}
scroll.contentSize = CGSizeMake(self.view.frame.size.width * numberOfViews, self.view.frame.size.height);
[self.view addSubview:scroll];
[scroll release];
}

My question is how can I detect which page the user is on? Like logging "1" for page 1, "2" for page 2, etc.

Thanks!

You can get the current page number by using the scroll view's content offset and its width.

int currentPage = (scrollView.contentOffset.x / scrollView.frame.width) + 1;
NSLog(@"current page: %d", currentPage);

You should take y offset into account if the scrolling is done vertically.

if you want to know on which page the user is while he scrolls you should add your object as Delegate object (UIScrollViewDelegate) you can then use the

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

call and calculate the page like in emptystacks answer.

btw. the calculation is float, if you need to know when exactly the page is fully scrolled you should use float.

Actually, it's even better to use int currentPage = (scrollView.contentOffset.x / scrollView.frame.width) + 1.5;

That extra .5 means the page change happens when the pages are halfway across the view rather than being rounded left.