List like Fleck iOS app - ios

Question

I want to create a scroll view like Fleck app (https://itunes.apple.com/us/app/fleck-the-bigger-picture/id619977675). When you scroll items change his height. One increases the other decreases
I created this. But this work queerly. Perhaps there are similar elements. They could help me...
#interface FleckView()
#property (strong, nonatomic) NSMutableArray* items;
#property (strong, nonatomic) NSMutableArray* cells;
#property (assign, nonatomic) CGFloat old_y;
#property (assign, nonatomic) CGFloat step;
#end
#implementation FleckView
#define kCellHeight 80.0
#define kCellHeightActive 320.0
int counter = 0;
float diff = (kCellHeightActive - kCellHeight) / kCellHeight; // 3.5
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
-(void) loadItems: (NSMutableArray*) items{
self.old_y = 0;
self.step = 0;
self.delegate = self;
self.cells = [[NSMutableArray alloc] init];
self.items = items;
self.contentSize = CGSizeMake(320, kCellHeightActive + (self.items.count) * kCellHeight);
//add first
UIView *view = [self.items objectAtIndex:0];
view.frame = CGRectMake(0, 0, 320, kCellHeightActive);
[self.cells addObject: view];
[self addSubview:view];
//add other
for(int i = 1; i < self.items.count; i++){
UIView *view = [self.items objectAtIndex:i];
view.frame = CGRectMake(0, ((i - 1) * kCellHeight) + kCellHeightActive, 320, kCellHeight);
[self.cells addObject: view];
[self addSubview:view];
}
}
////MAIN WORK
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
counter = (scrollView.contentOffset.y) / kCellHeight ;
self.step = scrollView.contentOffset.y - self.old_y;
self.old_y = scrollView.contentOffset.y;
if(counter < self.items.count){
[self setHeightRow: counter + 1];
}
}
-(void) setHeightRow: (int) rowNum{
UIView *cell_prev = [self.cells objectAtIndex: rowNum - 1];
UIView *cell = [self.cells objectAtIndex: rowNum];
CGFloat height = cell.frame.size.height;
height = height + (self.step * diff);
if(height < 90)
height = 80;
CGFloat height_prev = kCellHeightActive + kCellHeight - height;
NSLog(#"HEIGHT_PREV: %f", height_prev);
NSLog(#"HEIGHT: %f", height);
CGFloat y_prev = counter * kCellHeight;
CGFloat y = y_prev + height_prev;
NSLog(#"___Y_PREV: %f", y_prev);
NSLog(#"___Y: %f", y);
cell_prev.frame = CGRectMake(0, y_prev, 320, height_prev);
cell.frame = CGRectMake(0, y, 320, height);
}
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
float bottom = counter * kCellHeight;
float top = (counter + 1) * kCellHeight;
if(targetContentOffset->y > kCellHeight / 2 + counter * kCellHeight){
targetContentOffset->y = top;
}
else{
targetContentOffset->y = bottom;
}
}