由于UICollectionView的用处较多，每次使用都去网上查阅资料，今天抽空来总结一下UICollectionView的使用

collectionView和tableView最大的不同之处就是需要自定义cell,所以第一步自定义collectionViewCell

.h文件

@interface MoreMaterialCell : UICollectionViewCell
@property (strong, nonatomic) UIImageView *topImage;
@property (strong, nonatomic) UILabel *botlabel;
@end

.m文件

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        _topImage  = [[UIImageView alloc] initWithFrame:CGRectMake(10, 0, 70, 70)];
        _topImage.backgroundColor = [UIColor redColor];
        [self.contentView addSubview:_topImage];
        
        _botlabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 80, 70, 30)];
        _botlabel.textAlignment = NSTextAlignmentCenter;
        _botlabel.textColor = [UIColor blueColor];
        _botlabel.font = [UIFont systemFontOfSize:15];
        _botlabel.backgroundColor = [UIColor purpleColor];
        [self.contentView addSubview:_botlabel];
    }
    
    return self;
}

-在MoreMaterialVC(继承自UIcollectionView)中实现一下三个协议：

@interface MoreMaterialVC ()<UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>

MoreMaterialVC控制器中的具体代码如下：

//  Created by apple on 2018/12/17.
//  Copyright © 2018 apple. All rights reserved.

#import "MoreMaterialVC.h"
#import "MoreMaterialCell.h"
@interface MoreMaterialVC ()<UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>

@end

@implementation MoreMaterialVC

static NSString * const reuseIdentifier = @"Cell";

- (void)viewDidLoad {
    [super viewDidLoad];
    //1.初始化layout
    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    //设置collectionView滚动方向
    //    [layout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
    //设置headerView的尺寸大小
    layout.headerReferenceSize = CGSizeMake(self.view.frame.size.width, 100);
    //该方法也可以设置itemSize
    layout.itemSize =CGSizeMake(110, 150);
    
    //2.初始化collectionView
    self.collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    [self.view addSubview:self.collectionView];
    self.collectionView.backgroundColor = [UIColor clearColor];
    
    //3.注册collectionViewCell
    //注意，此处的ReuseIdentifier 必须和 cellForItemAtIndexPath 方法中 一致 均为 cellId
    [self.collectionView registerClass:[self.collectionView class] forCellWithReuseIdentifier:@"cellId"];
    
    //注册headerView  此处的ReuseIdentifier 必须和 cellForItemAtIndexPath 方法中 一致  均为reusableView
    [self.collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"reusableView"];
    
    //4.设置代理
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
    
  
  
}

#pragma mark collectionView代理方法
//返回section个数
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 3;
}
//每个section的item个数
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 9;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    
    MoreMaterialCell *cell = (MoreMaterialCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"cellId" forIndexPath:indexPath];
    
    cell.botlabel.text = [NSString stringWithFormat:@"{%ld,%ld}",(long)indexPath.section,(long)indexPath.row];
    
    cell.backgroundColor = [UIColor yellowColor];
    
    return cell;
}

//设置每个item的尺寸
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(90, 130);
}

//footer的size
//- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
//{
//    return CGSizeMake(10, 10);
//}

//header的size
//- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
//{
//    return CGSizeMake(10, 10);
//}

//设置每个item的UIEdgeInsets
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    return UIEdgeInsetsMake(10, 10, 10, 10);
}

//设置每个item水平间距
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 10;
}


//设置每个item垂直间距
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 15;
}

//通过设置SupplementaryViewOfKind 来设置头部或者底部的view，其中 ReuseIdentifier 的值必须和 注册是填写的一致，本例都为 “reusableView”
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"reusableView" forIndexPath:indexPath];
    headerView.backgroundColor =[UIColor grayColor];
    UILabel *label = [[UILabel alloc] initWithFrame:headerView.bounds];
    label.text = @"这是collectionView的头部";
    label.font = [UIFont systemFontOfSize:20];
    [headerView addSubview:label];
    return headerView;
}

//点击item方法
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    MoreMaterialCell *cell = (MoreMaterialCell *)[collectionView cellForItemAtIndexPath:indexPath];
    NSString *msg = cell.botlabel.text;
    NSLog(@"%@",msg);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
@end