HATransitionLayout.m

//
//  HATransitionLayout.m
//  Paper
//
//  Created by Heberti Almeida on 11/02/14.
//  Copyright (c) 2014 Heberti Almeida. All rights reserved.
//

#import "HATransitionLayout.h"

static NSString *kOffsetH = @"offsetH";
static NSString *kOffsetV = @"offsetV";

@implementation HATransitionLayout

// set the completion progress of the current transition.
//
- (void)setTransitionProgress:(CGFloat)transitionProgress
{
    [super setTransitionProgress:transitionProgress];
    
    // return the most recently set values for each key
    CGFloat offsetH = [self valueForAnimatedKey:kOffsetH];
    CGFloat offsetV = [self valueForAnimatedKey:kOffsetV];
    _offset = UIOffsetMake(offsetH, offsetV);
}

// called by the HATransitionController class while updating its transition progress, animating
// the collection view items in an out of stack mode.
//
- (void)setOffset:(UIOffset)offset
{
    // store the floating-point values with out meaningful keys for our transition layout object
    [self updateValue:offset.horizontal forAnimatedKey:kOffsetH];
    [self updateValue:offset.vertical forAnimatedKey:kOffsetV];
    _offset = offset;
}

// return the layout attributes for all of the cells and views in the specified rectangle
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *attributes = [super layoutAttributesForElementsInRect:rect];
    
    for (UICollectionViewLayoutAttributes *currentAttribute in attributes)
    {
        if (currentAttribute.representedElementCategory != UICollectionElementCategorySupplementaryView) {
            CGPoint currentCenter = currentAttribute.center;
            CGPoint updatedCenter = CGPointMake(currentCenter.x, currentCenter.y + self.offset.vertical);
            currentAttribute.center = updatedCenter;
        }
        
        if (currentAttribute.representedElementCategory == UICollectionElementCategorySupplementaryView) {
            currentAttribute.frame = self.collectionView.bounds;
        }

    }

    return attributes;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    // returns the layout attributes for the item at the specified index path
    UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForItemAtIndexPath:indexPath];
    CGPoint currentCenter = attributes.center;
    CGPoint updatedCenter = CGPointMake(currentCenter.x + self.offset.horizontal, currentCenter.y + self.offset.vertical);
    attributes.center = updatedCenter;
    return attributes;
}


@end