Loop an UIScrollView [duplicate] - iphone

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UIScrollView. Any thoughts on implementing “infinite” scroll/zoom?
I've got an UIScrollView and in it different images(about 30). I'd like to make it possible, when user reaches the last image to show the first one after it and so on. And I want to implement the same feature with the first image(to go to the last one).
I'd like to loop the images smoothly that user won't even notice that he is making another loop.
What is the best way to achieve this?
Thanks.

Answer 1

I've just done this. I have an array of images to add to the scrollview so I first of all add the last one to the scrollview, then run through the array to add all the images and then after that, add the first one from the array again.
Have a look through this code:
#import "MainViewController.h"
#import "MainView.h"
#define WIDTH_OF_SCROLL_PAGE 320
#define HEIGHT_OF_SCROLL_PAGE 352
#define WIDTH_OF_IMAGE 320
#define HEIGHT_OF_IMAGE 352
#define LEFT_EDGE_OFSET 0
#implementation MainViewController
#synthesize scrollView, slideImages;
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad {
scrollView = [[UIScrollView alloc] init];
CGRect scrollFrame;
scrollFrame.origin.x = 0;
scrollFrame.origin.y = 0;
scrollFrame.size.width = WIDTH_OF_SCROLL_PAGE;
scrollFrame.size.height = HEIGHT_OF_SCROLL_PAGE;
scrollView = [[UIScrollView alloc] initWithFrame:scrollFrame];
scrollView.bounces = YES;
scrollView.pagingEnabled = YES;
scrollView.delegate = self;
scrollView.userInteractionEnabled = YES;
slideImages = [[NSMutableArray alloc] init];
[slideImages addObject:#"welcome-small.jpg"];
[slideImages addObject:#"football-small.jpg"];
[slideImages addObject:#"dancing-small.jpg"];
[slideImages addObject:#"celebration-small.jpg"];
//add the last image first
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:[slideImages objectAtIndex:([slideImages count]-1)]]];
imageView.frame = CGRectMake(LEFT_EDGE_OFSET, 0, WIDTH_OF_IMAGE, HEIGHT_OF_IMAGE);
[scrollView addSubview:imageView];
[imageView release];
for (int i = 0;i<[slideImages count];i++) {
//loop this bit
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:[slideImages objectAtIndex:i]]];
imageView.frame = CGRectMake((WIDTH_OF_IMAGE * i) + LEFT_EDGE_OFSET + 320, 0, WIDTH_OF_IMAGE, HEIGHT_OF_IMAGE);
[scrollView addSubview:imageView];
[imageView release];
//
}
//add the first image at the end
imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:[slideImages objectAtIndex:0]]];
imageView.frame = CGRectMake((WIDTH_OF_IMAGE * ([slideImages count] + 1)) + LEFT_EDGE_OFSET, 0, WIDTH_OF_IMAGE, HEIGHT_OF_IMAGE);
[scrollView addSubview:imageView];
[imageView release];
[scrollView setContentSize:CGSizeMake(WIDTH_OF_SCROLL_PAGE * ([slideImages count] + 2), HEIGHT_OF_IMAGE)];
[scrollView setContentOffset:CGPointMake(0, 0)];
[self.view addSubview:scrollView];
[self.scrollView scrollRectToVisible:CGRectMake(WIDTH_OF_IMAGE,0,WIDTH_OF_IMAGE,HEIGHT_OF_IMAGE) animated:NO];
[super viewDidLoad];
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
int currentPage = floor((self.scrollView.contentOffset.x - self.scrollView.frame.size.width / ([slideImages count]+2)) / self.scrollView.frame.size.width) + 1;
if (currentPage==0) {
//go last but 1 page
[self.scrollView scrollRectToVisible:CGRectMake(WIDTH_OF_IMAGE * [slideImages count],0,WIDTH_OF_IMAGE,HEIGHT_OF_IMAGE) animated:NO];
} else if (currentPage==([slideImages count]+1)) {
[self.scrollView scrollRectToVisible:CGRectMake(WIDTH_OF_IMAGE,0,WIDTH_OF_IMAGE,HEIGHT_OF_IMAGE) animated:NO];
}
}
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)dealloc {
[scrollView release];
[slideImages release];
[super dealloc];
}
#end
I then use scrollViewDidEndDecelerating to check where in the scroll the user is, and then jump them to the 2nd image or last but 1 image so they can scroll continuously... Sorry if I haven't explained it well - short of time! But this code is working fine for me on the device..

Answer 2

You can also have infinite scrolling without paging. Here is a great explanation at WWDC