Determining the amount of scroll using UIScrollView and PageControl

For the application I'm working on, I need a scrollview with paging along with several views (in this case tableviews). Setting this option (using the Apple PageControl example) is quite simple, and I have no problem working with it regarding scrolling and linking between pages. I want tableviews to be almost similar to thumbnail views of table views in scrollview. As soon as you click one, it will open or zoom in so that the table screen spans the entire screen. Again, tweaking this question is not really a problem, I can make the views inside scrollview any size I want and click, I'm sure I can work when I get to this part. :)

My problem is this: in any given view, no matter what page you are on, I want the next page and previous page to be slightly visible on the right and left, respectively. Of course, the first page will only have one page shown on the right side, or the left side for the last page. Again, by setting the x-origin of the views (tabular views), I can get the first page to look right. However, as soon as you view the problem, it becomes obvious, namely, that the screen scrolls too far.

Breaking it, I think my main problem is that I cannot change the amount of scroll that is performed when switching pages.

I would appreciate any help I can get, thanks.

Appdelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : NSObject <UIApplicationDelegate, UIScrollViewDelegate> {
UIWindow *window;
UIView *background;
UIScrollView *scrollView;
UIPageControl *pageControl;
NSMutableArray *viewControllers;

// To be used when scrolls originate from the UIPageControl
// I've commented this out (and all references to it) since I've disabled user interaction with the UIPageControl
//BOOL pageControlUsed;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UIView *background;

@property (nonatomic, retain) IBOutlet UIScrollView *scrollView;
@property (nonatomic, retain) IBOutlet UIPageControl *pageControl;
@property (nonatomic, retain) NSMutableArray *viewControllers;

- (IBAction)changePage:(id)sender;

@end  

AppDelegate.m

#import "AppDelegate.h"
#import "MyViewController.h"

static NSUInteger kNumberOfPages = 4;

@interface AppDelegate (PrivateMethods)

- (void)loadScrollViewWithPage:(int)page;
- (void)scrollViewDidScroll:(UIScrollView *)sender;

@end

@implementation AppDelegate

@synthesize window, scrollView, pageControl, viewControllers, background;

- (void)dealloc {
[background release];
[viewControllers release];
[scrollView release];
[pageControl release];
[window release];
[super dealloc];
}

- (void)applicationDidFinishLaunching:(UIApplication *)application {

background.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"Background.png"]];

// view controllers are created lazily
// in the meantime, load the array with placeholders which will be replaced on demand
NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (unsigned i = 0; i < kNumberOfPages; i++) {
    [controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;
[controllers release];

// a page is the width of the scroll view
scrollView.pagingEnabled = YES;
scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
scrollView.showsHorizontalScrollIndicator = NO;
scrollView.showsVerticalScrollIndicator = NO;
scrollView.scrollsToTop = NO;
scrollView.delegate = self;

pageControl.numberOfPages = kNumberOfPages;
pageControl.currentPage = 0;

// pages are created on demand
// load the visible page
// load the page on either side to avoid flashes when the user starts scrolling
[self loadScrollViewWithPage:0];
[self loadScrollViewWithPage:1];
}

- (void)loadScrollViewWithPage:(int)page {
if (page < 0) return;
if (page >= kNumberOfPages) return;

// replace the placeholder if necessary
MyViewController *controller = [viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null]) {
    controller = [[MyViewController alloc] initWithPageNumber:page];
    [viewControllers replaceObjectAtIndex:page withObject:controller];
    [controller release];
}

// add the controller view to the scroll view
if (nil == controller.view.superview) {
    CGRect frame = CGRectMake(50, 50, 220, 330);
    frame.origin.x = 50 + (250 * page);
    frame.origin.y = 50;
    controller.view.frame = frame;
    [scrollView addSubview:controller.view];
}
}

- (void)scrollViewDidScroll:(UIScrollView *)sender {
// We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
// which a scroll event generated from the user hitting the page control triggers updates from
// the delegate method. We use a boolean to disable the delegate logic when the page control is used.
/*if (pageControlUsed) {
    // do nothing - the scroll was initiated from the page control, not the user dragging
    return;
}*/

// Switch the indicator when more than 50% of the previous/next page is visible
CGFloat pageWidth = scrollView.frame.size.width;
int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
pageControl.currentPage = page;

// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];

// A possible optimization would be to unload the views+controllers which are no longer visible
}

// At the begin of scroll dragging, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
//pageControlUsed = NO;
}

// At the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
//pageControlUsed = NO;
}

- (IBAction)changePage:(id)sender {
int page = pageControl.currentPage;

// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];

// update the scroll view to the appropriate page
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
[scrollView scrollRectToVisible:frame animated:YES];

// Set the boolean used when scrolls originate from the UIPageControl. See       scrollViewDidScroll: above.
//pageControlUsed = YES;
}

@end