How do I change the current page for Ray Wenderlich's UIScrollView Tutorial?

Question

I am using Ray Wenderlich's (Matt Galloway's) tutorial on UIScrollViews: http://www.raywenderlich.com/10518/how-to-use-uiscrollview-to-scroll-and-zoom-content

I am using the section, "Paging with UIScrollView" in my app. This works great when you always want the page to load on 0, but I would like the current page to be dynamic. I will be passing this information in based on which thumbnail the user picked from the previous view controller, which is an NSInteger called "listIndex."

How do I change the current page to my listIndex? I have tried changing

self.pageControl.currentPage = 0;

to

self.pageControl.currentPage = self.listIndex;

in viewDidLoad, but this doesn't seem to help - possibly because it's getting reset in loadVisiblePages?

Thank you so much for the help! Here's the code:

- (void)loadVisiblePages {
    // First, determine which page is currently visible
    CGFloat pageWidth = self.scrollView.frame.size.width;

    NSInteger page = (NSInteger)floor((self.scrollView.contentOffset.x * 2.0f + pageWidth) / (pageWidth * 2.0f));

    // Update the page control
    self.pageControl.currentPage = page;


     // Work out which pages you want to load
     NSInteger firstPage = page - 1;
     NSInteger lastPage = page + 1;

     // Purge anything before the first page
     for (NSInteger i=0; i<firstPage; i++) {
         [self purgePage:i];
     }

     // Load pages in our range
     for (NSInteger i=firstPage; i<=lastPage; i++) {
         [self loadPage:i];
     }

    // Purge anything after the last page
        for (NSInteger i=lastPage+1; i<self.pageImages.count; i++) {
            [self purgePage:i];
        }
}


- (void)purgePage:(NSInteger)page {
   if (page < 0 || page >= self.pageImages.count) {
         // If it's outside the range of what you have to display, then do nothing
        return;
    }

    // Remove a page from the scroll view and reset the container array
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView != [NSNull null]) {
        [pageView removeFromSuperview];
        [self.pageViews replaceObjectAtIndex:page withObject:[NSNull null]];
    }
}

- (void)loadPage:(NSInteger)page {
    if (page < 0 || page >= self.pageImages.count) {
        // If it's outside the range of what you have to display, then do nothing
        return;
    }

    // 1
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView == [NSNull null]) {
        // 2
        CGRect frame = self.scrollView.bounds;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0.0f;

        // 3
        UIImageView *newPageView = [[UIImageView alloc] initWithImage:[self.pageImages   objectAtIndex:page]];
        newPageView.contentMode = UIViewContentModeScaleAspectFit;
        newPageView.frame = frame;
        [self.scrollView addSubview:newPageView];
        // 4
        [self.pageViews replaceObjectAtIndex:page withObject:newPageView];
    }
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    // Load the pages that are now on screen
    [self loadVisiblePages];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSMutableString *myHTML = [[NSMutableString alloc] initWithString:@"<html><head><style type='text/css'> p {font-family:sans-serif; text-shadow: 3px 4px 5px #000; color:#FFF; position: absolute; bottom:0; font-size:10pt; font-weight:bold; margin-bottom:5px;}</style><body><p>"];

    [myHTML appendString:self.caption];

    [myHTML appendString:@"</p></body></html>"];

    [captionWebView loadHTMLString:myHTML baseURL:nil];

    self.pageImages = [NSMutableArray array];

    for (int i=0; i < [imageList count]; i++) {
        NSString *path = [(Image *)[imageList objectAtIndex:i] path];
        [self.pageImages addObject:[UIImage imageNamed:path]];
    }


    NSInteger pageCount = self.pageImages.count;

    // 2
    self.pageControl.currentPage = 0;
    //self.pageControl.currentPage = self.listIndex; //Tried this
    self.pageControl.numberOfPages = pageCount;

    // 3
    self.pageViews = [[NSMutableArray alloc] init];
    for (NSInteger i = 0; i < pageCount; ++i) {
        [self.pageViews addObject:[NSNull null]];
    }




}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];


    // add this in order UIScrollView work with Auto layout

    if (IS_WIDESCREEN) {

        self.scrollView.frame = CGRectMake(0, 0, 320, 468);

    } else {

        self.scrollView.frame = CGRectMake(0, 0, 320, 380);

    }

    // 4
    CGSize pagesScrollViewSize = self.scrollView.frame.size;
    self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageImages.count, pagesScrollViewSize.height);

    // 5
    [self loadVisiblePages];
}

- (void)viewWillDisappear:(BOOL)animated {

    // add this in order UIScrollView work with Auto layout

    if (IS_WIDESCREEN) {

        self.scrollView.contentSize = CGSizeMake(320, 468);

    } else {

        self.scrollView.contentSize = CGSizeMake(320, 380);

    }

}

Answer 1

Try setting the scrollview's initial contentOffset in viewWillAppear: :

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    // Set up the content size of the scroll view
    CGSize pagesScrollViewSize = self.scrollView.frame.size;
    self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageImages.count, pagesScrollViewSize.height);

    // Set initial content offset of scrollview
    self.scrollView.contentOffset = CGPointMake(pagesScrollViewSize.width * self.listIndex, self.scrollView.contentOffset.y);

    // Load the initial set of pages that are on screen
    [self loadVisiblePages];
}

How do I change the current page for Ray Wenderlich's UIScrollView Tutorial?

Question

1 answers

solution1
2 ACCPTED 2013-08-21 00:13:40

How do I change the current page for Ray Wenderlich's UIScrollView Tutorial?

Question

1 answers

solution1 2 ACCPTED 2013-08-21 00:13:40

solution1
2 ACCPTED 2013-08-21 00:13:40