思路：

collectionView如何将子类目录签入，可放置在footerView内，形成一种嵌入的错觉。

建立好模型可以更清晰的将数据对应放入。

1.先子类化一个view里面用于显示三级目录。

2.在子类话一个collectionView下面用到就可以直接用了，子类一个cell。

#import 
    
     @interface ViewController : UIViewController@end#import "ViewController.h"#import "DataModel.h"#import "LXJCollectionView.h"@interface ViewController ()@property (nonatomic, strong)NSMutableArray * dataArr;@end@implementation ViewController-(NSMutableArray *)dataArr{    if (_dataArr == nil) {        _dataArr = [[NSMutableArray alloc]init];    }    return _dataArr;}- (void)viewDidLoad {    [super viewDidLoad];    [self createModel];}- (void)createModel{    NSArray * image = @[@[@"image1",@"image2",@"image3"],                        @[@"image4",@"image5",@"image6"],                        @[@"image7",@"image8"]];        NSArray * title = @[@[@"项目一",@"项目二",@"项目三"],                        @[@"项目四",@"项目五",@"项目六"],                        @[@"项目七",@"项目八"]];        NSArray * bigTitle = @[@"大类一",@"大类二",@"大类三"];        NSArray * sonsServe = @[@[@[@"修电脑1",@"修洗衣机",@"理发",@"收垃圾",@"阿道夫",@"阿道夫",],@[@"修电脑2",@"修洗衣机",@"理发",@"收垃圾",@"阿道夫",@"阿道夫",@"修电脑bug",@"修洗衣机",@"理发",@"收垃圾",@"阿道夫",@"阿道夫"],@[@"修洗衣机3",@"理发",@"收垃圾",@"阿道夫",@"阿道夫",@"修电脑"]],                                                        @[@[@"理发1",@"收垃圾",@"阿道夫",@"阿道夫"],@[@"阿道夫2"],@[@"理发3"]],                                                        @[@[@"阿道夫1",@"修电脑",@"收垃圾",@"阿道夫"],@[@"修洗衣机2"],@[@"理发3"]]];        for (int i = 0; i < 3; i++) {                DataModel * model = [[DataModel alloc]init];        model.ID = i;        model.name = bigTitle[i];        for (int j = 0; j < [image[i] count]; j++) {            DataModel * sonModel = [[DataModel alloc]init];            sonModel.name = title[i][j];            sonModel.ID = j;            sonModel.imageName = image[i][j];                        for (int h = 0; h < [sonsServe[i][j] count]; h++) {                DataModel * grandSon = [[DataModel alloc]init];                grandSon.name = sonsServe[i][j][h];                grandSon.ID = h;                [sonModel.sons addObject:grandSon];            }                        [model.sons addObject:sonModel];        }        [self.dataArr addObject:model];    }        LXJCollectionView * collectionView = [[LXJCollectionView alloc]initWithFrame:CGRectMake(0, 64, self.view.frame.size.width, self.view.frame.size.height-64)];    collectionView.data = self.dataArr;    [self.view addSubview:collectionView];}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>#import "JSONModel.h"@interface DataModel : JSONModel@property (nonatomic, assign)NSInteger ID;@property (nonatomic, copy)NSString * name;@property (nonatomic, strong)NSMutableArray * sons;@property (nonatomic, copy)NSString * imageName;@end#import "DataModel.h"@implementation DataModel-(NSMutableArray *)sons{    if (_sons == nil) {        _sons = [[NSMutableArray alloc]init];    }    return _sons;}//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>#import 
     
      @interface LXJCollectionView : UIView@property (nonatomic, strong)NSArray * data;@property (nonatomic, strong)NSArray * secondData;@end#define kSelfWidth self.frame.size.width#define kSelfHeight self.frame.size.height#import "LXJCollectionView.h"#import "LXJHomeCollectionViewCell.h"#import "DataModel.h"#import "SecondView.h"@interface LXJCollectionView ()
      
       {    UICollectionView * _collectionView;}@property (nonatomic, strong)NSMutableDictionary * stateDic;@end@implementation LXJCollectionView- (instancetype)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        self.backgroundColor = [UIColor whiteColor];        [self createCollectionView];            }    return self;}#pragma mark - create- (void)createCollectionView{    UICollectionViewFlowLayout * flowLayout = [[UICollectionViewFlowLayout alloc]init];    flowLayout.minimumInteritemSpacing = 0;    flowLayout.minimumLineSpacing = 0;    flowLayout.itemSize = CGSizeMake(kSelfWidth/3.0, kSelfWidth/3.0);        _collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, kSelfWidth, kSelfHeight) collectionViewLayout:flowLayout];    _collectionView.delegate = self;    _collectionView.dataSource = self;    _collectionView.backgroundColor = [UIColor whiteColor];    [self addSubview:_collectionView];        //注册    [_collectionView registerClass:[LXJHomeCollectionViewCell class] forCellWithReuseIdentifier:@"cellID"];    [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"headerView"];    [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footerView"];    //状态字典 需要用这个字典来记录点击的Cell它的二级目录对应的三级目录是开还是合    //并且记录每个section下的footerView是开还是合    //分开两张情况记录 是因为：    //如果点击了section = 1,row = 1;后 section对应的footerview应该是张开的，而后在点击section = 1,row = 2;的时候 section对应的footer还是张开的 如果只记住了一种的话footerview就会合上    //所以需要记入section开合状态 并且seciton.row开合状态 最后将section.row的状态赋予section，不直接记录section.row是因为//    - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section    //这个方法最多只能拿到section 所以只能两个都记录    _stateDic = [[NSMutableDictionary alloc]init];}#pragma mark - UICollection DataSource-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    NSString * cellID = @"cellID";    LXJHomeCollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellID forIndexPath:indexPath];    if (cell == nil) {        cell = [[LXJHomeCollectionViewCell alloc]init];    }    NSArray * arry = [_data[indexPath.section] sons];    DataModel * model = arry[indexPath.row];    cell.titleImage.image = [UIImage imageNamed:model.imageName];    cell.titleLabel.text = model.name;    return cell;}-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{    DataModel * model = _data[section];    return model.sons.count;}-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{    return _data.count;}-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{    UICollectionReusableView * headerView = nil;    UICollectionReusableView * footerView = nil;    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {                headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"headerView" forIndexPath:indexPath];        headerView.backgroundColor = [UIColor lightGrayColor];        [headerView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];        UILabel * label = [[UILabel alloc]initWithFrame:CGRectMake(12, 0, kSelfWidth, 40)];        [headerView addSubview:label];        label.textColor = [UIColor darkTextColor];        label.font = [UIFont systemFontOfSize:14.0f];        label.textAlignment = NSTextAlignmentLeft;        label.text = [_data[indexPath.section] name];        return headerView;    }else if ([kind isEqualToString:UICollectionElementKindSectionFooter])    {        footerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footerView" forIndexPath:indexPath];                NSString *key = [NSString stringWithFormat:@"%ld",indexPath.section];        NSInteger createID = [[_stateDic valueForKey:key] integerValue];                [footerView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];        if (createID == 1) {                        NSInteger lineNum = (_secondData.count+2)/3;//计算出行 加二是为了当数为4 7 这一类的数是计算出的结果为正确行数                        SecondView * secondView = [[SecondView alloc]initWithFrame:CGRectMake(0, 0, kSelfWidth, 40*lineNum)];            [footerView addSubview:secondView];            secondView.secondData = _secondData;                    }        return footerView;    }else{        return nil;    }    }-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section{    return CGSizeMake(kSelfWidth, 53);}- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section{    NSString *key = [NSString stringWithFormat:@"%ld",section];    NSInteger createID = [[_stateDic valueForKey:key] integerValue];    if (createID == 1) {                NSInteger lineNum = (_secondData.count+2)/3;        return CGSizeMake(kSelfWidth, 40*lineNum);    }    return CGSizeMake(0, 0);}- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{    NSArray * arry1 = [_data[indexPath.section] sons];    DataModel * model = arry1[indexPath.row];    _secondData = model.sons;        NSString *key = [NSString stringWithFormat:@"%ld",indexPath.section];    //0合 1开    NSString * key1 = [NSString stringWithFormat:@"%ld",10000*(indexPath.section+1)+indexPath.row+1];    NSInteger createID = [[_stateDic valueForKey:key1] integerValue];        if (createID == 0) {        createID = 1;    }else{        createID = 0;    }        //将所有的footerview重新掷为闭合状态    NSArray * allKey = _stateDic.allKeys;    for (int i = 0; i < allKey.count; i++) {        [_stateDic setValue:@(0) forKey:allKey[i]];    }        [_stateDic setValue:@(createID) forKeyPath:key1];//section.row 对应的开合状态    [_stateDic setValue:@(createID) forKey:key];      //section 对应的开合状态    [_collectionView reloadData];}- (void)setData:(NSArray *)data{    _data = data;    [_collectionView reloadData];}@end//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>#import 
       
        @interface LXJHomeCollectionViewCell : UICollectionViewCell@property (nonatomic, strong)UIImageView * titleImage;@property (nonatomic, strong)UITextView * titleLabel;@end#import "LXJHomeCollectionViewCell.h"@implementation LXJHomeCollectionViewCell- (instancetype)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        self.backgroundColor = [UIColor whiteColor];        [self createContent];            }    return self;}- (void)createContent{    float width = [UIScreen mainScreen].bounds.size.width;    CGFloat gap = (width - 43.75*3)/6.0;        _titleImage = [[UIImageView alloc]initWithFrame:CGRectMake(gap, 12, 43.75, 43.75)];    [self.contentView addSubview:_titleImage];        _titleLabel = [[UITextView alloc]initWithFrame:CGRectMake(5, CGRectGetMaxY(_titleImage.frame), width/3.0-10, 35)];    _titleLabel.editable = NO;    _titleLabel.userInteractionEnabled = NO;    _titleLabel.font = [UIFont systemFontOfSize:12.0f];    _titleLabel.textAlignment = NSTextAlignmentCenter;    _titleLabel.textColor = [UIColor darkTextColor];    [self.contentView addSubview:_titleLabel];}@end//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>#import 
        
         @interface SecondView : UIView@property (nonatomic, strong)NSArray * secondData;@end#import "SecondView.h"#import "DataModel.h"#define kWidth self.frame.size.width#define kHeight self.frame.size.height@implementation SecondView- (void)setSecondData:(NSArray *)secondData{    _secondData = secondData;    float btnWidth = kWidth/3.0;    float btnHeight = 40;        for (int i = 1; i <= secondData.count; i++) {                DataModel * model = secondData[i-1];                NSInteger lineNum = (i+2)/3;        UIButton * button = [[UIButton alloc]initWithFrame:CGRectMake(btnWidth*(i-1)- (lineNum-1)*kWidth,(lineNum-1) *btnHeight, btnWidth, btnHeight)];        [button setTitle:model.name forState:UIControlStateNormal];        [button.layer setBorderColor:[UIColor orangeColor].CGColor];        [button.layer setBorderWidth:0.5];        button.backgroundColor = [UIColor clearColor];        [button setTitleColor:[UIColor orangeColor] forState:UIControlStateNormal];        button.layer.cornerRadius = 4;        button.layer.masksToBounds = YES;        [self addSubview:button];            }}@end
        
       
      
     
    

Demo :