继承关系

UICollectionViewLayout

UICollectionViewLayout

ViewController.m里
#import "ViewController.h"
#import "TestCollectionViewCell.h"
#import "DetailCollectionViewController.h"
#import "HeaderCollectionReusableView.h"
@interface ViewController ()<UICollectionViewDelegateFlowLayout,UICollectionViewDataSource>
@end
@implementation ViewController
NSString *identifier =  @"cell";
NSString *headerIdentifier = @"header";
NSString *footerIdentifier = @"footer";
- (void)viewDidLoad {
    [super viewDidLoad];
    // 创建布局对象
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    // 1.设置最小行间距
    flowLayout.minimumLineSpacing = 50;
    // 2.设置最小列间距 (大于最小列间距后 自适应距离大小)
    flowLayout.minimumInteritemSpacing = 20;
    // 3.设置Item大小
    flowLayout.itemSize = CGSizeMake(50, 50);
    // 4.设置滚动方向 (水平 和 垂直)
    flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;
    // 5.设置集合视图内边距大小(上 左 下 右)
    flowLayout.sectionInset = UIEdgeInsetsMake(20, 20, 20, 20);
    // 6.设置header区域大小 (设置大小就要返回视图)
    flowLayout.headerReferenceSize = CGSizeMake(414, 70);
    // 7.设置footer区域大小
//    flowLayout.footerReferenceSize = CGSizeMake(414, 40);

// 注册增补视图(没有头和尾 只有增补视图)  UICollectionReusableView增补视图基类
    // header注册
    [collectionView registerClass:[HeaderCollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerIdentifier];
    // footer注册
   //    [collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerIdentifier];
    // 创建UICollectionView之前必须先创建布局对象
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:[UIScreen mainScreen].bounds collectionViewLayout:flowLayout];
    // 设置属性
    collectionView.backgroundColor = [UIColor whiteColor];// 默认是黑色
    // 是否显示垂直反向指示标    collectionView.showsVerticalScrollIndicator = NO;
    // 设置代理
    collectionView.delegate = self;
    collectionView.dataSource = self;
    // 注册cell
    [collectionView registerClass:[TestCollectionViewCell class] forCellWithReuseIdentifier:identifier];
     // 添加到视图上 
    [self.view addSubview:collectionView];
  }
#pragma --- UICollectionViewDelegateFlowLayout ---
// 返回cell (必须实现一般自定义,因为属性少)
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    TestCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
    cell.contentView.backgroundColor = [UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0 blue:arc4random()%256/255.0 alpha:1];
    cell.imgView.image = [UIImage imageNamed:@"2"];
       return cell;
}
// 设置每个分区返回多少Item (必须实现)
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return 13;
}
// 设置区域个数
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
    return 3;
}
// 返回增补视图
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    // 如果是头视图
    if (kind == UICollectionElementKindSectionHeader) {
        // 从重用池里面取
        HeaderCollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:headerIdentifier forIndexPath:indexPath]; 
       headerView.backgroundColor = [UIColor brownColor];
        headerView.titleLabel.text = @"测试";
        return headerView;
    }else{
//        UICollectionReusableView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerIdentifier forIndexPath:indexPath];
//        footerView.backgroundColor = [UIColor orangeColor];
//        return footerView;
        return nil;
    }
}
// 点击每个item触发的方法
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    NSLog(@"%ld --- %ld",indexPath.section,indexPath.row);
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init]; 
    DetailCollectionViewController *detailVC = [[DetailCollectionViewController alloc] 
initWithCollectionViewLayout:flowLayout];
    detailVC.collectionView.backgroundColor = [UIColor whiteColor];
    [self.navigationController pushViewController:detailVC animated:YES];
}
// 指定哪些路径可以被点击
-(BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    if (indexPath.section == 0) {
        return NO;
    }
    return YES;}
// 返回内边距的上左下右的边距
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
       return UIEdgeInsetsMake(30, 30, 30, 30);
}

HeaderCollectionReusableView.h里
#import <UIKit/UIKit.h>
@interface HeaderCollectionReusableView : UICollectionReusableView
@property (nonatomic,strong) UILabel *titleLabel;
@end

#import "HeaderCollectionReusableView.h"
@implementation HeaderCollectionReusableView
-(instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        self.titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 0, 200, 40)];
        _titleLabel.backgroundColor = [UIColor redColor];
        [self addSubview:_titleLabel];
    }
    return self;
}
@end

TestCollectionViewCell.h里
#import <UIKit/UIKit.h>
@interface TestCollectionViewCell : UICollectionViewCell
@property (nonatomic,strong) UIImageView *imgView;
@end
TestCollectionViewCell.h 里
@implementation TestCollectionViewCell- (instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        // 跟cell等大的imgView
        self.imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];
        [self.contentView addSubview:_imgView];
    }
    return self;
}
@end