How do I create a UICollectionView with column and row headers?

Question

I want to create a UICollectionView that looks like this:

It won't be scrollable or editable. I'm currently wondering how to write the layout for this. I'm guessing it won't be a subclass of UICollectionViewFlowLayout. I can think of a number of ways, but was curious if there was any "right" way. The cells will be animate-able.

Should each row or column be its own section?

Answer 1

I've done something like what you want with a subclass of UICollectionViewFlowLayout. It looks like this,

 @implementation MultpleLineLayout {
    NSInteger itemWidth;
    NSInteger itemHeight;
}

-(id)init {
    if (self = [super init]) {
        itemWidth = 80;
        itemHeight = 80;
    }
    return self;
}

-(CGSize)collectionViewContentSize {
    NSInteger xSize = [self.collectionView numberOfItemsInSection:0] * (itemWidth + 2); // the 2 is for spacing between cells.
    NSInteger ySize = [self.collectionView numberOfSections] * (itemHeight + 2);
    return CGSizeMake(xSize, ySize);
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)path {
    UICollectionViewLayoutAttributes* attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:path];
    NSInteger xValue;
    attributes.size = CGSizeMake(itemWidth,itemHeight);
    xValue = itemWidth/2 + path.row * (itemWidth +2);
    NSInteger yValue = itemHeight + path.section * (itemHeight +2);
    attributes.center = CGPointMake(xValue, yValue);
    return attributes;
}


-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {
    NSInteger minRow =  (rect.origin.x > 0)?  rect.origin.x/(itemWidth +2) : 0; // need to check because bounce gives negative values  for x.
    NSInteger maxRow = rect.size.width/(itemWidth +2) + minRow;
    NSMutableArray* attributes = [NSMutableArray array];
    for(NSInteger i=0 ; i < self.collectionView.numberOfSections; i++) {
        for (NSInteger j=minRow ; j < maxRow; j++) {
            NSIndexPath* indexPath = [NSIndexPath indexPathForItem:j inSection:i];
            [attributes addObject:[self layoutAttributesForItemAtIndexPath:indexPath]];
        }
    }
    return attributes;
}

The data is arranged as an array of arrays where each inner array supplies the data for one horizontal row. With the values I have in there now, and using your data as an example, the view looked like this,

This is the code I haven the view controller,

@interface ViewController ()
@property (strong,nonatomic) UICollectionView *collectionView;
@property (strong,nonatomic) NSArray *theData;
@end

@implementation ViewController

- (void)viewDidLoad {
    self.theData = @[@[@"",@"A",@"B",@"C"],@[@"1",@"115",@"127",@"132"],@[@"2",@"",@"",@"153"],@[@"3",@"",@"199",@""]];

    MultpleLineLayout *layout = [[MultpleLineLayout alloc] init];
    self.collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    self.collectionView.dataSource = self;
    self.collectionView.delegate = self;
    layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    self.view.backgroundColor = [UIColor blackColor];
    [self.view addSubview:self.collectionView];
    [self.collectionView registerNib:[UINib nibWithNibName:@"CustomDataCell" bundle:nil] forCellWithReuseIdentifier:@"DataCell"];
}


- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section {
    return [self.theData[section] count];
}

- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView {
    return [self.theData count];
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView  cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    DataCell *cell = [collectionView  dequeueReusableCellWithReuseIdentifier:@"DataCell" forIndexPath:indexPath];
    cell.label.text = self.theData[indexPath.section][indexPath.row];
    return cell;
}