SectionIndexTitles for a UICollectionView

Question

So I implemented a proper TableView with a search functionality and sectionIndexTitles. Now, I am trying to implement a UICollectionView

Answer 1

You can now simply use (as of iOS 10.3)

optional func indexTitles(for collectionView: UICollectionView) -> [String]?

Which expects an array like: ['A', 'B' ,'C'] as its return value.

Answer 2

You can provide this header by implementing and returning a value for the following function for UICollectionViewDataSource

collectionView:viewForSupplementaryElementOfKind:atIndexPath:

Note that the size of the header will be from the height value of the CGRect returned from UICollectionViewFlowLayoutDelegate method collectionView:layout:referenceSizeForHeaderInSection:

Answer 3

I had a similar requirement (for a horizontal collection view) and ended up building an index view subclass myself.

I plan to open-source it but that will likely have to wait until next month, so here's a stub to get you started:

YMCollectionIndexView.h

@interface YMCollectionIndexView : UIControl

- (id) initWithFrame:(CGRect)frame indexTitles:(NSArray *)indexTitles;

// Model
@property (strong, nonatomic) NSArray *indexTitles; // NSString
@property (readonly, nonatomic) NSUInteger currentIndex;
- (NSString *)currentIndexTitle;

@end

YMCollectionIndexView.m

#import "YMCollectionIndexView.h"

@interface YMCollectionIndexView ()
@property (readwrite, nonatomic) NSUInteger currentIndex;
@property (strong, nonatomic) NSArray *indexLabels;
@end

@implementation YMCollectionIndexView

- (id) initWithFrame:(CGRect)frame indexTitles:(NSArray *)indexTitles {
    self = [super initWithFrame:frame];
    if (self) {
        self.indexTitles = indexTitles;
        self.currentIndex = 0;
        // add pan recognizer
    }
    return self;
}

- (void)setIndexTitles:(NSArray *)indexTitles {
    if (_indexTitles == indexTitles) return;
    _indexTitles = indexTitles;
    [self.indexLabels makeObjectsPerformSelector:@selector(removeFromSuperview)];
    [self buildIndexLabels];
}

- (NSString *)currentIndexTitle {
    return self.indexTitles[self.currentIndex];
}

#pragma mark - Subviews

- (void) buildIndexLabels {
    CGFloat cumulativeItemWidth = 0.0; // or height in your (vertical) case
    for (NSString *indexTitle in self.indexTitles) {
            // build and add label
        // add tap recognizer
    }
    self.indexLabels = indexLabels;
}

#pragma mark - Gestures

- (void) handleTap:(UITapGestureRecognizer*)recognizer {
    NSString *indexTitle = ((UILabel *)recognizer.view).text;
    self.currentIndex = [self.indexTitles indexOfObject:indexTitle];
    [self sendActionsForControlEvents:UIControlEventTouchUpInside];
}

// similarly for pan recognizer

@end

In your view controller:

- (void)viewDidLoad {
    [super viewDidLoad];
    [self.collectionIndexView addTarget:self action:@selector(indexWasTapped:) forControlEvents:UIControlEventTouchUpInside];
    // similarly for pan recognizer
}

- (void)indexWasTapped:(id)sender {
    [self.collectionView scrollToIndexPath:...];
}

// similarly for pan recognizer

Answer 4

As of iOS 14 (which has severely enhanced UICollectionView, in particular for making UITableView obsolete), this works as expected by implementing the delegate method indexTitles.