ANDistributedFlowLayout/ANDistributedFlowLayout.m at master · argon/ANDistributedFlowLayout · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
//
//  ANDistributedFlowLayout.m
//
//  Originally: KTCenterFlowLayout.m
//  Created by Kyle Truscott on 10/9/14.
//  Copyright (c) 2014 keighl. All rights reserved.
//
//  Modified by Andrew Naylor on 30/07/14
//

#import "ANDistributedFlowLayout.h"

@implementation ANDistributedFlowLayout

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *superAttributes = [NSMutableArray arrayWithArray:[super layoutAttributesForElementsInRect:rect]];

    NSMutableDictionary *rowCollections = [NSMutableDictionary new];

    // Collect attributes by their midY coordinate.. i.e. rows!

    for (UICollectionViewLayoutAttributes *itemAttributes in superAttributes)
    {
        // Normalize the midY to others in the row
        // with variable cell heights the midYs can be ever so slightly
        // different.
        CGFloat midYRound = roundf(CGRectGetMidY(itemAttributes.frame));
        CGFloat midYPlus = midYRound + 1;
        CGFloat midYMinus = midYRound - 1;
        NSNumber *key;

        if (rowCollections[@(midYPlus)])
            key = @(midYPlus);

        if (rowCollections[@(midYMinus)])
            key = @(midYMinus);

        if (!key)
            key = @(midYRound);

        if (!rowCollections[key])
            rowCollections[key] = [NSMutableArray new];

        [(NSMutableArray *) rowCollections[key] addObject:itemAttributes];
    }

    CGFloat collectionViewWidth = CGRectGetWidth(self.collectionView.bounds) - self.collectionView.contentInset.left - self.collectionView.contentInset.right;


    // Adjust the items in each row
    [rowCollections enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {

        NSArray *itemAttributesCollection = obj;
        NSInteger itemsInRow = [itemAttributesCollection count];

        // Sum the width of all elements in the row
        CGFloat aggregateItemWidths = 0.f;
        for (UICollectionViewLayoutAttributes *itemAttributes in itemAttributesCollection)
            aggregateItemWidths += CGRectGetWidth(itemAttributes.frame);

        // |-x-x-x-x-| ... calculate the total space left
        CGFloat aggregateInteritemSpacing = collectionViewWidth - aggregateItemWidths;

        CGFloat interItemSpacing = aggregateInteritemSpacing / (itemsInRow + 1);

        // Adjust each item's position to be centered
        CGRect previousFrame = CGRectZero;
        for (UICollectionViewLayoutAttributes *itemAttributes in itemAttributesCollection)
        {
            CGRect itemFrame = itemAttributes.frame;

            itemFrame.origin.x = CGRectGetMaxX(previousFrame) + interItemSpacing;

            itemAttributes.frame = itemFrame;
            previousFrame = itemFrame;
        }
    }];

    return superAttributes;
}

@end