UiScrollView not working the way i want to

Question

I have been trying for a while to get UIScrollView to get working. Ive come so far that it does indeed scroll but not to the ViewController i want to. And i have no idea how to do it so some help from here would be nice.

This is how the code looks like for ViewController.m

- (void)viewDidLoad {
    [super viewDidLoad];

    NSMutableArray *controllers = [[NSMutableArray alloc] init];

    [controllers addObject:[NSNull null]];
    [controllers addObject:[NSNull null]];

    self.viewControllers = controllers;

    self.scrollView.pagingEnabled = YES;
    self.scrollView.contentSize =
    CGSizeMake(CGRectGetWidth(self.scrollView.frame) * 2, CGRectGetHeight(self.scrollView.frame));
    self.scrollView.showsHorizontalScrollIndicator = YES;
    self.scrollView.delegate = self;

    self.pageControl.numberOfPages = 2;
    self.pageControl.currentPage = 0;

    [self loadScrollViewWithPage:0];
    [self loadScrollViewWithPage:1];

    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)loadScrollViewWithPage:(NSUInteger)page
{
    if (page >= 2)
        return;

    // replace the placeholder if necessary
    ViewController2 *controller = [self.viewControllers objectAtIndex:page];
    if ((NSNull *)controller == [NSNull null])
    {
        controller = [[ViewController2 alloc] init];
        [self.viewControllers replaceObjectAtIndex:page withObject:controller];
    }

    // add the controller's view to the scroll view
    if (controller.view.superview == nil)
    {
        CGRect frame = self.scrollView.frame;
        frame.origin.x = CGRectGetWidth(frame) * page;
        frame.origin.y = 0;
        controller.view.frame = frame;

        [self addChildViewController:controller];
        [self.scrollView addSubview:controller.view];
        [controller didMoveToParentViewController:self];
    }
}

// at the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    // switch the indicator when more than 50% of the previous/next page is visible
    CGFloat pageWidth = CGRectGetWidth(self.scrollView.frame);
    NSUInteger page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    self.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
}

- (void)gotoPage:(BOOL)animated
{
    NSInteger page = self.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 bounds = self.scrollView.bounds;
    bounds.origin.x = CGRectGetWidth(bounds) * page;
    bounds.origin.y = 0;
    [self.scrollView scrollRectToVisible:bounds animated:animated];
}

- (IBAction)changePage:(id)sender
{
    [self gotoPage:YES];    // YES = animate
}

So what happens is the first view gets loaded. And i can scroll but it scrolls to an empty view. What i would like to do is that it scrolls to ViewController2

How can i implement for it to do so? (horizontally)

EDIT1, trying to implement what matt suggested

- (void)viewDidLoad {
    [super viewDidLoad];

    self.vcIdentifiers = @[@"PageContentViewController", @"PageContentViewController1"];

    // Create page view controller
    self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PageViewController"];
    self.pageViewController.dataSource = self;

    UIViewController *startingViewController = [self viewControllerAtIndex:0];
    NSArray *viewControllers = @[startingViewController];
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];

    self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 30);

    [self addChildViewController:_pageViewController];
    [self.view addSubview:_pageViewController.view];
    [self.pageViewController didMoveToParentViewController:self];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (PageContentViewController *)viewControllerAtIndex:(NSUInteger)index
{
    if (([self.vcIdentifiers count] == 0) || (index >= self.vcIdentifiers.count)) {
        return nil;
    }


    // Create a new view controller and pass suitable data.
    PageContentViewController *pageContentViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PageContentViewController"];
    pageContentViewController.titleText = self.pageTitles[index];
    pageContentViewController.pageIndex = index;

    return pageContentViewController;
}


- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    NSUInteger index = ((PageContentViewController*) viewController).pageIndex;

    if ((index == 0) || (index == NSNotFound)) {
        return nil;
    }

    index--;
    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    NSUInteger index = ((PageContentViewController*) viewController).pageIndex;

    if (index == NSNotFound) {
        return nil;
    }

    index++;
    if (index == [self.pageTitles count]) {
        return nil;
    }
    return [self viewControllerAtIndex:index];
}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
{
    //return [self.pageTitles count];
    return 2;
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
{
    return 0;
}

I am thinking of using the storyboard id's that my viewcontrollers have, svaed in VCidentifiers.

What i dont get is how to instantiate the viewcontrollers in the method viewControllerAtIndex. The way it is written now, it will only create PageContentViewController, when it should for index 0 create PageContentViewController and for index 1 PageContent2Controller.

What am i missing?

Answer 1

A scroll view is for scrolling between existing views, not for dynamically loading views from view controllers. You can use view controllers in this way, and we used to have to do it sometimes, but (as you've discovered) it is difficult.

I recommend that you drop your scroll view and use UIPageViewController in a scroll style instead. It solves all the problem for you when what you want you to do is scroll between view controllers' views.