效果图

实现逻辑和原理

就是在 didEndDisplayingCell 方法中通过indexPathsForVisibleItems 接口获取当前可见的cell对应的indexPath， 然后获取到item最小的那一个，即可，同时，还要在 willDisplayCell 方法中直接设置标题的选中属性，否则
由于重用机制，导致选中的展示错乱

代码

//
//  LBLinkedContentView.m
//  LBTwoLinkedScrollingCollectionView
//
//  Created by mac on 2024/6/25.
//#import "LBLinkedContentView.h"
#import "LBLinkedContentViewTittleCell.h"
#import "LBLinkedContentViewContentCell.h"@interface LBLinkedContentView () <UICollectionViewDelegate, UICollectionViewDataSource>@property (nonatomic, strong) UICollectionView *titleView;
@property (nonatomic, strong) UICollectionView *contentView;@property (nonatomic, strong) NSMutableArray *titleArray;
@property (nonatomic, strong) NSMutableArray *contentArray;@property (nonatomic, strong) NSIndexPath *selectedGroupIndex;@end@implementation LBLinkedContentView- (instancetype)initWithFrame:(CGRect)frame
{if (self = [super initWithFrame:frame]) {[self configData];[self setUpUI];}return self;
}- (void)setUpUI
{[self addSubview:self.titleView];[self addSubview:self.contentView];[self.titleView reloadData];[self.contentView reloadData];self.selectedGroupIndex = [NSIndexPath indexPathForRow:0 inSection:0];LBLinkedContentViewTittleCell *titleCell = [self.titleView cellForItemAtIndexPath:self.selectedGroupIndex];titleCell.selected = YES;
}#pragma mark - configData- (void)configData
{for (int i = 0; i < 10; i ++)  {NSString *title = [NSString stringWithFormat:@"%d",i];[self.titleArray addObject:title];NSMutableArray *array = [NSMutableArray array];for (int j = 0; j < 10; j ++) {NSString *content = [NSString stringWithFormat:@"第%d分区第%d条", i,j];[array addObject:content];}[self.contentArray addObject:array];}
}#pragma mark - data Delegate- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{if (collectionView == self.contentView) {LBLinkedContentViewContentCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([LBLinkedContentViewContentCell class]) forIndexPath:indexPath];NSString *title = self.contentArray[indexPath.section][indexPath.item];[cell updateWithContent:title];return cell;}LBLinkedContentViewTittleCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([LBLinkedContentViewTittleCell class]) forIndexPath:indexPath];[cell updateWithIndexPath:indexPath];return cell;
}- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{if (collectionView == self.titleView) {return 1;}return self.contentArray.count;
}- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{return 10;
}- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath
{if (collectionView == self.titleView) {if (self.selectedGroupIndex && [self.selectedGroupIndex compare:indexPath] == NSOrderedSame) {cell.selected = YES;} else {cell.selected = NO;}}
}- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath
{if (collectionView == self.contentView) {[self handleGroupViewWithIndex:nil];}
}#pragma mark - private- (void)handleGroupViewWithIndex:(NSIndexPath *)indexPathCell
{NSArray <NSIndexPath *> *visibleIndexPaths = [self.contentView indexPathsForVisibleItems];if (!visibleIndexPaths.count) {return;}NSInteger section = indexPathCell ? indexPathCell.section : [self.contentView numberOfSections] - 1;for (NSIndexPath *indexPath in visibleIndexPaths) {if (indexPath.section < section) {section = indexPath.section;}}NSIndexPath *groupIndexPath = [NSIndexPath indexPathForItem:section inSection:0];if(self.selectedGroupIndex && [self.selectedGroupIndex compare:groupIndexPath] != NSOrderedSame) {LBLinkedContentViewTittleCell *cell = [self.titleView cellForItemAtIndexPath:self.selectedGroupIndex];cell.selected = NO;self.selectedGroupIndex = groupIndexPath;LBLinkedContentViewTittleCell *titleCell = [self.titleView cellForItemAtIndexPath:groupIndexPath];titleCell.selected = YES;[self.titleView scrollToItemAtIndexPath:groupIndexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];}
}#pragma mark - lazy load- (UICollectionView *)titleView
{if (!_titleView) {UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];layout.minimumLineSpacing = 29;layout.minimumInteritemSpacing = 29;layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;layout.itemSize = CGSizeMake(40, 50);_titleView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.bounds), 60) collectionViewLayout:layout];[_titleView registerClass:[LBLinkedContentViewTittleCell class] forCellWithReuseIdentifier:NSStringFromClass([LBLinkedContentViewTittleCell class])];_titleView.delegate = self;_titleView.dataSource = self;}return _titleView;
}- (UICollectionView *)contentView
{if (!_contentView) {UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];layout.minimumLineSpacing = 10;layout.minimumInteritemSpacing = 10;layout.itemSize = CGSizeMake(100, 80);layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;layout.sectionInset = UIEdgeInsetsMake(0, 40, 0, 40);_contentView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 80, CGRectGetWidth(self.bounds), 80) collectionViewLayout:layout];[_contentView registerClass:[LBLinkedContentViewContentCell class] forCellWithReuseIdentifier:NSStringFromClass([LBLinkedContentViewContentCell class])];_contentView.delegate = self;_contentView.dataSource = self;_contentView.backgroundColor = [UIColor yellowColor];}return _contentView;
}- (NSMutableArray *)titleArray
{if (!_titleArray) {_titleArray = [NSMutableArray array];}return _titleArray;
}- (NSMutableArray *)contentArray
{if (!_contentArray) {_contentArray = [NSMutableArray array];}return _contentArray;
}@end

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