Following what has been said, you can show thousand of elements using only a limited amount of resources (and yes, it's a bit of a Flyweight pattern indeed). Here's some code that might help you do what you want.
The UntitledViewController class just contains a UIScroll and sets itself as its delegate. We have an NSArray with NSString instances inside as data model (there could be potentially thousands of NSStrings in it), and we want to show each one in a UILabel, using horizontal scrolling. When the user scrolls, we shift the UILabels to put one on the left, another on the right, so that everything is ready for the next scroll event.
Here's the interface, rather straightforward:
@interface UntitledViewController : UIViewController <UIScrollViewDelegate>
{
@private
UIScrollView *_scrollView;
NSArray *_objects;
UILabel *_detailLabel1;
UILabel *_detailLabel2;
UILabel *_detailLabel3;
}
@end
And here's the implementation for that class:
@interface UntitledViewController ()
- (void)replaceHiddenLabels;
- (void)displayLabelsAroundIndex:(NSInteger)index;
@end
@implementation UntitledViewController
- (void)dealloc
{
[_objects release];
[_scrollView release];
[_detailLabel1 release];
[_detailLabel2 release];
[_detailLabel3 release];
[super dealloc];
}
- (void)viewDidLoad
{
[super viewDidLoad];
_objects = [[NSArray alloc] initWithObjects:@"first", @"second", @"third",
@"fourth", @"fifth", @"sixth", @"seventh", @"eight", @"ninth", @"tenth", nil];
_scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 460.0)];
_scrollView.contentSize = CGSizeMake(320.0 * [_objects count], 460.0);
_scrollView.showsVerticalScrollIndicator = NO;
_scrollView.showsHorizontalScrollIndicator = YES;
_scrollView.alwaysBounceHorizontal = YES;
_scrollView.alwaysBounceVertical = NO;
_scrollView.pagingEnabled = YES;
_scrollView.delegate = self;
_detailLabel1 = [[UILabel alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 460.0)];
_detailLabel1.textAlignment = UITextAlignmentCenter;
_detailLabel1.font = [UIFont boldSystemFontOfSize:30.0];
_detailLabel2 = [[UILabel alloc] initWithFrame:CGRectMake(320.0, 0.0, 320.0, 460.0)];
_detailLabel2.textAlignment = UITextAlignmentCenter;
_detailLabel2.font = [UIFont boldSystemFontOfSize:30.0];
_detailLabel3 = [[UILabel alloc] initWithFrame:CGRectMake(640.0, 0.0, 320.0, 460.0)];
_detailLabel3.textAlignment = UITextAlignmentCenter;
_detailLabel3.font = [UIFont boldSystemFontOfSize:30.0];
// We are going to show all the contents of the _objects array
// using only these three UILabel instances, making them jump
// right and left, replacing them as required:
[_scrollView addSubview:_detailLabel1];
[_scrollView addSubview:_detailLabel2];
[_scrollView addSubview:_detailLabel3];
[self.view addSubview:_scrollView];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
[_scrollView flashScrollIndicators];
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self displayLabelsAroundIndex:0];
}
- (void)didReceiveMemoryWarning
{
// Here you could release the data source, but make sure
// you rebuild it in a lazy-loading way as soon as you need it again...
[super didReceiveMemoryWarning];
}
#pragma mark -
#pragma mark UIScrollViewDelegate methods
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
// Do some initialization here, before the scroll view starts moving!
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
[self replaceHiddenLabels];
}
- (void)displayLabelsAroundIndex:(NSInteger)index
{
NSInteger count = [_objects count];
if (index >= 0 && index < count)
{
NSString *text = [_objects objectAtIndex:index];
_detailLabel1.frame = CGRectMake(320.0 * index, 0.0, 320.0, 460.0);
_detailLabel1.text = text;
[_scrollView scrollRectToVisible:CGRectMake(320.0 * index, 0.0, 320.0, 460.0) animated:NO];
if (index < (count - 1))
{
text = [_objects objectAtIndex:(index + 1)];
_detailLabel2.frame = CGRectMake(320.0 * (index + 1), 0.0, 320.0, 460.0);
_detailLabel2.text = text;
}
if (index > 0)
{
text = [_objects objectAtIndex:(index - 1)];
_detailLabel3.frame = CGRectMake(320.0 * (index - 1), 0.0, 320.0, 460.0);
_detailLabel3.text = text;
}
}
}
- (void)replaceHiddenLabels
{
static const double pageWidth = 320.0;
NSInteger currentIndex = ((_scrollView.contentOffset.x - pageWidth) / pageWidth) + 1;
UILabel *currentLabel = nil;
UILabel *previousLabel = nil;
UILabel *nextLabel = nil;
if (CGRectContainsPoint(_detailLabel1.frame, _scrollView.contentOffset))
{
currentLabel = _detailLabel1;
previousLabel = _detailLabel2;
nextLabel = _detailLabel3;
}
else if (CGRectContainsPoint(_detailLabel2.frame, _scrollView.contentOffset))
{
currentLabel = _detailLabel2;
previousLabel = _detailLabel1;
nextLabel = _detailLabel3;
}
else
{
currentLabel = _detailLabel3;
previousLabel = _detailLabel1;
nextLabel = _detailLabel2;
}
currentLabel.frame = CGRectMake(320.0 * currentIndex, 0.0, 320.0, 460.0);
currentLabel.text = [_objects objectAtIndex:currentIndex];
// Now move the other ones around
// and set them ready for the next scroll
if (currentIndex < [_objects count] - 1)
{
nextLabel.frame = CGRectMake(320.0 * (currentIndex + 1), 0.0, 320.0, 460.0);
nextLabel.text = [_objects objectAtIndex:(currentIndex + 1)];
}
if (currentIndex >= 1)
{
previousLabel.frame = CGRectMake(320.0 * (currentIndex - 1), 0.0, 320.0, 460.0);
previousLabel.text = [_objects objectAtIndex:(currentIndex - 1)];
}
}
@end
Hope this helps!