UIScrollView Infinite Scrolling
- by Ben Robinson
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.contentOffset.x);
}
As the scrolling happens the log reads:
1286.500000
1285.500000
1284.500000
1283.500000
1282.500000
1281.500000
1280.500000
Then, when pageNumber<4 (we're getting near the beginning):
4479.500000
4479.500000
Great! - but the numbers should continue to go down in the 4,000s but the next log entries read:
1278.000000
1277.000000
1276.500000
1275.500000
etc....
Continiuing from where it left off!
Just for the record, if scrolled slowly the log reads:
1294.500000
1290.000000
1284.500000
1280.500000
4476.000000
4476.000000
4473.000000
4470.000000
4467.500000
4464.000000
4460.500000
4457.500000
etc....
Any ideas????
Thanks
Ben.
