/*

     File: APLTransitionLayout.m

 Abstract: Helps in the transition the of cell positions based on the pinch gesture position.

  Version: 1.1

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#import "APLTransitionLayout.h"

static NSString *kOffsetH = @"offsetH";

static NSString *kOffsetV = @"offsetV";

@implementation APLTransitionLayout

// 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 APLTransitionManager 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)

    {

        CGPoint currentCenter = currentAttribute.center;

        CGPoint updatedCenter = CGPointMake(currentCenter.x + self.offset.horizontal, currentCenter.y + self.offset.vertical);

        currentAttribute.center = updatedCenter;

    }

    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