UIScrollView, Pull down effect similar to CalcBot - objective-c

Question

I'm trying to make a UI similar to CalcBot where you can pull down the view controller with your finger and it reveals a hidden background view.
I think this is done with the UIScrollView but cannot work out the exact method to have for example 2x Horizontal views with one of them having a vertical.
I do have the horizontal scroll working fine, i'm just stuck with how I can make screen 1 pull down with a vertical scroller.
Any tips or pointers would be appreciated.
Thanks Aaron

Answer 1

You can have nested scrollviews to get scrolling working in both directions. Let's have a vertical scroller inside a horizontal scroller (though you can very well do it the other way round too), so views 3 and 1 get into a vertical scrollview, which in turn gets inside a horizontal scroller along with view 2.
You could create such a view hierarchy in code (probably in the main viewcontroller's viewDidLoad). The following snippet assumes view1, view2 and view3 as webviews.
CGRect bounds = self.view.bounds;
// main guy is a horizontal scroller
UIScrollView *hScrollView = [[UIScrollView alloc] initWithFrame:bounds];
hScrollView.contentSize = CGSizeMake(bounds.size.width * 2, bounds.size.height);
hScrollView.delegate = self;
[self.view addSubview:hScrollView];
// the horizontal scroller contains a vertical scroller
UIScrollView *vScrollView = [[UIScrollView alloc] initWithFrame:bounds];
vScrollView.contentSize = CGSizeMake(bounds.size.width, bounds.size.height * 2);
vScrollView.delegate = self;
[hScrollView addSubview:vScrollView];
// add view3 and view1 to the vertical scroller
UIWebView *view3 = [[UIWebView alloc] initWithFrame:bounds];
[view3 loadHTMLString:#"<h1>3</h1>" baseURL:nil];
[vScrollView addSubview:view3];
UIWebView *view1 = [[UIWebView alloc] initWithFrame:CGRectOffset(bounds, 0, bounds.size.height)];
[view1 loadHTMLString:#"<h1>1</h1>" baseURL:nil];
[vScrollView addSubview:view1];
vScrollView.contentOffset = CGPointMake(0, bounds.size.height);
// add view2 to the horizontal scroller
UIWebView *view2 = [[UIWebView alloc] initWithFrame:CGRectOffset(bounds, bounds.size.width, 0)];
[view2 loadHTMLString:#"<h1>2</h1>" baseURL:nil];
[hScrollView addSubview:view2];
// enable paging in both directions
hScrollView.pagingEnabled = TRUE;
vScrollView.pagingEnabled = TRUE;
That would have you scrolling in both directions but that would also let you scroll-right from view3 to view2. If you want to prevent that, you should disable scrolling on hScrollView whenever the vScollView is showing view3. You can do that in scrollViewDidEndDecelerating: in the delegate of vScrollView. Something like:
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
if (scrollView == self.verticalScrollView) {
self.horizontalScrollView.scrollEnabled = (self.verticalScrollView.contentOffset.y > self.view.bounds.origin.y);
}
}