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UIScrollView Infinite Scrolling

Asked 2010-08-07T11:35:29.553
17

I'm attempting to setup a scrollview with infinite (horizontal) scrolling.

Scrolling forward is easy - I have implemented scrollViewDidScroll, and when the contentOffset gets near the end I make the scrollview contentsize bigger and add more data into the space (i'll have to deal with the crippling effect this will have later!)

My problem is scrolling back - the plan is to see when I get near the beginning of the scroll view, then when I do make the contentsize bigger, move the existing content along, add the new data to the beginning and then - importantly adjust the contentOffset so the data under the view port stays the same.

This works perfectly if I scroll slowly (or enable paging) but if I go fast (not even very fast!) it goes mad! Heres the code:

- (void) scrollViewDidScroll:(UIScrollView *)scrollView {

    float pageNumber = scrollView.contentOffset.x / 320;
    float pageCount = scrollView.contentSize.width / 320;

    if (pageNumber > pageCount-4) {
        //Add 10 new pages to end
        mainScrollView.contentSize = CGSizeMake(mainScrollView.contentSize.width + 3200, mainScrollView.contentSize.height);
        //add new data here at (320*pageCount, 0);
    }

    //*** the problem is here - I use updatingScrollingContent to make sure its only called once (for accurate testing!)
    if (pageNumber < 4 && !updatingScrollingContent) {

        updatingScrollingContent = YES;

        mainScrollView.contentSize = CGSizeMake(mainScrollView.contentSize.width + 3200, mainScrollView.contentSize.height);
        mainScrollView.contentOffset = CGPointMake(mainScrollView.contentOffset.x + 3200, 0);
        for (UIView *view in [mainContainerView subviews]) {
            view.frame = CGRectMake(view.frame.origin.x+3200, view.frame.origin.y, view.frame.size.width, view.frame.size.height);
        }
        //add new data here at (0, 0);      
    }

    //** MY CHECK!
    NSLog(@"%f", mainScrollView.contentOf
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1 Answer

5

(hope I'm posting this correctly - I'm new here!?)

mvds was spot on - thanks - subclassing UIScrollView works perfectly - I'm yet to implement the shifting and loading of new data, but I have a UIScrollView that scrolls round in an endless loop!

Heres the code:

#import "BRScrollView.h"

@implementation BRScrollView

- (id)awakeFromNib:(NSCoder *)decoder {
    offsetAdjustment = 0;
    [super initWithCoder:decoder];
    return self;
}

- (void)setContentOffset:(CGPoint)contentOffset {

    float realOffset = contentOffset.x + offsetAdjustment;

    //This happens when contentOffset has updated correctly - there is no need for the adjustment any more
    if (realOffset < expectedContentOffset-2000 || realOffset > expectedContentOffset+2000) {
        offsetAdjustment = 0;
        realOffset = contentOffset.x;
    }

    float pageNumber = realOffset / 320;
    float pageCount = self.contentSize.width / 320;

    if (pageNumber > pageCount-4) {
        offsetAdjustment -= 3200;
        realOffset -= 3200;
    }

    if (pageNumber < 4) {
        offsetAdjustment += 3200;
        realOffset += 3200; 
    }

    //Save expected offset for next call, and pass the real offset on
    expectedContentOffset = realOffset;     
    [super setContentOffset:CGPointMake(realOffset, 0)];


}

- (void)dealloc {
    [super dealloc];
}


@end

Notes:

If you actually want an infinite loop, you'd need to adjust the numbers - this codes notices when you get near the edge and moves you to just beyond the middle

My contentSize is 6720 (21 pages)

I'm only interest in scrolling horizontally, so only save the x values and hard code the y to 0!

Ben

answered 2010-08-09T11:58:10.907

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