转载自:http://jinqianchina.github.io/2015/08/16/UICollectionview%E7%9A%84%E4%BD%BF%E7%94%A8%E8%AF%A6%E8%A7%A3/

UICollectionview的使用详解

1. 三个代理<uicollectionviewdatasource,uicollectionviewdelegate,uicollectionviewdelegateflowlayout>
   前两个的用法和tableView的很像，第三个是布局的协议。（注意：头视图尾视图都是由代理方法获得，而且需要写注册，缺少了也不行。） 注册以后，就不需要再去管理复用的问题了。这点就很简单。这个如果用好的话，会非常的简单。
2. item（即cell）的布局原理（类似tableView）
3. header/footer View的布局原理
   都是继承于UICollectionReusableView，并且必须要从dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:这个代理方法中获取，而且根据不同的kind作为headerView或者footerView，切记：collectionView中头部视图和尾部视图也需要注册

下面直接上代码，看注释即可：

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>{

}
@property (strong, nonatomic)UICollectionView *collectionView;

@end

ViewController.m

#import "ViewController.h"
#import "NewSceneCollectionHeaderView.h"
#import "NewSceneCollectionFooterView.h"
#import "NewSceneCollectionViewCell.h"

@interface ViewController ()

@end

//cell、header、footerView 标识
static NSString *cellIdentifier = @"NewSceneCollectionViewCell";
static NSString *headerIdentifier = @"NewSceneCollectionHeaderView";
static NSString *footerIdentifier = @"NewSceneCollectionFooterView";

@implementation ViewController

- (void)viewDidLoad
{
      [super viewDidLoad];
     //创建布局对象
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    //flowlaout的属性，确定是水平滚动，还是垂直滚动
    flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;

    //接下来就在创建collectionView的时候初始化，就很方便了（能直接带上layout）
    self.collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 200, 320, 280) collectionViewLayout:flowLayout];
    self.collectionView.backgroundColor = [UIColor grayColor]; 

    //指定数据源和代理
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;

    //添加到主页面上去
    [self.view addSubview:self.collectionView];

    //collectionCell的注册
    [self.collectionView registerClass:[NewSceneCollectionViewCell class] forCellWithReuseIdentifier:cellIdentifier];

    //collection头视图的注册。  注意：奇葩的地方来了，头视图和尾部视图也得注册
    [self.collectionView registerClass:[NewSceneCollectionHeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerIdentifier];
    [self.collectionView registerClass:[NewSceneCollectionFooterView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:footerIdentifier];

      /*另一种方式
      //从Xib上注册
    UINib *nib = nil;
    nib = [UINib nibWithNibName:cellIdentifier bundle:nil];
    [self.collectionView registerNib:nib
                 forCellWithReuseIdentifier:cellIdentifier];
    //注册headerview和footerview
    nib = [UINib nibWithNibName:headerIdentifier bundle:nil];
    [self.collectionView registerNib:nib forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerIdentifier];
    nib = [UINib nibWithNibName:footerIdentifier bundle:nil];
    [self.collectionView registerNib:nib forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerIdentifier];
    */
      [self.view addSubview:self.collectionView];
}

/********************************************************
 *UICollectionViewDataSource/Delegate/DelegateFlowLayout
 ********************************************************/
#pragma mark  UICollectionViewDataSource/Delegate

//返回多少组（section），此方法不写默认是1组(跟tableview类似)
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 2;
}

#pragma mark required
//每组返回多少个Item，这个Item类似tableview中的cell
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 10;
}

//返回cell，这里构建Item（即cell）
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    //这里是自定义的cell
    NewSceneCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
    cell.backgroundColor = [UIColor redColor];
    return cell;
}

#pragma mark  optional
//自定义header/footerView
// The view that is returned must be retrieved from a call to -dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
//这里返回的view必须要从dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:这个方法中获取，而且根据不同的kind作为headerView或者footerView，切记：collectionView中头部视图和尾部视图也需要注册
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    UICollectionReusableView *reusableView = nil;
    if (UICollectionElementKindSectionHeader == kind) {
        //这里是自定义的头视图
        NewSceneCollectionHeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:headerIdentifier forIndexPath:indexPath];
        headerView.backgroundColor = [UIColor whiteColor];
        return headerView;
    }
    if (UICollectionElementKindSectionFooter == kind {
        //这里是自定义的尾视图
        NewSceneCollectionFooterView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:footerIdentifier forIndexPath:indexPath];
        footerView.backgroundColor = [UIColor whiteColor];
        return footerView;
    }
    return reusableView;
}

#pragma mark --UICollectionViewDelegateFlowLayout

//布局确定每个Item 的大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(100, 100);
}

//布局确定每个section内的Item距离section四周的间距 UIEdgeInsets
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    return UIEdgeInsetsMake(10, 10, 10, 10);
}

//返回每个section内上下两个Item之间的间距
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 10;
}
//返回每个section内左右两个Item之间的间距
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 10;
}

//返回headerView的尺寸
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
    CGFloat width = CGRectGetWidth(collectionView.bounds);
    CGFloat height = width + 86;
    return CGSizeMake(width, height);
}

//返回footerView的尺寸
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
{
    CGFloat width = CGRectGetWidth(collectionView.bounds);
    CGFloat height = 144;
    return CGSizeMake(width, height);
}

#pragma mark --UICollectionViewDelegate

//UICollectionView被选中时调用的方法
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NewSceneCollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
    cell.backgroundColor = [UIColor greenColor];
    NSLog(@"item======%ld",(long)indexPath.item);
    NSLog(@"row=======%ld",(long)indexPath.row);
    NSLog(@"section===%ld",(long)indexPath.section);
}

//返回这个UICollectionView是否可以被选择
-(BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}