iOS collectionView添加类似tableView的tableHeaderView

我们都知道UITableview有一个tableHeaderFooterView,这样我们在布局页面的时候，如果顶部有轮播图，可以直接把轮播图设置为tableView的HeaderFooterView,用起来很好用，但是，当我们用上CollectionView的时候，发现collectionView并没有HeaderFooterView这个属性，可是此时我们页面的架构是以colletction来实现的，而且collectionViewHeaderView也是有用到，如果有这样的需求，这里提供一种解决方案把：

我的思路是利用collectionView的contentInset和scrollViewInset属性，让collectionView的滚动区域和内容区域向下偏移一定的距离，这样，顶部就腾出空间，这个空间可以用来填补我们想要设置的header(可能是轮播图),创建一个自定义view,设置view的frame，然后让view的空间完全填充上面利用偏移腾出的空间，就可以完美解决上述问题了

思路是这样的思路，具体部分代码实现如下：

#import "ViewController.h"
#import "TYCustomCell.h"
#import "TYHeaderFooterView.h"

#define SCREEN_WIDTH   [UIScreen mainScreen].bounds.size.width

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

@property (nonatomic, strong) UICollectionView *collectionView;

@end

@implementation ViewController

-(UICollectionView *)collectionView{
    if (!_collectionView) {
        UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
        layout.itemSize = CGSizeMake(100, 100);
        layout.minimumInteritemSpacing = 10;
        layout.minimumLineSpacing = 10;
        layout.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);
        _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
        _collectionView.delegate = self;
        _collectionView.dataSource = self;
        _collectionView.backgroundColor = [UIColor whiteColor];
        [_collectionView registerClass:[TYCustomCell class] forCellWithReuseIdentifier:@"TYCustomCell"];
        [_collectionView registerClass:[TYHeaderFooterView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footer"];
        [_collectionView registerClass:[TYHeaderFooterView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header"];
        //设置滚动范围偏移200
        _collectionView.scrollIndicatorInsets = UIEdgeInsetsMake(200, 0, 0, 0);
        //设置内容范围偏移200
        _collectionView.contentInset = UIEdgeInsetsMake(200, 0, 0, 0);
        _collectionView.alwaysBounceVertical = YES;
    }
    return _collectionView;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self setupUI];
}

-(void)setupUI{
    
    //给collectionView添加子控件 这里是作为头部 记得设置y轴为负值
    UIView *header = [[UIView alloc] initWithFrame:CGRectMake(0, -200, SCREEN_WIDTH, 200)];
    header.backgroundColor = [UIColor cyanColor];
    [self.collectionView addSubview:header];
    
    //添加内容到视图上
    [self.view addSubview:self.collectionView];

}

#pragma mark - CollectonViewDataSource Delegate
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return 9;
}

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    TYCustomCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"TYCustomCell" forIndexPath:indexPath];
    cell.backgroundColor = [UIColor colorWithRed:arc4random_uniform(256)/255.0 green:arc4random_uniform(256)/255.0 blue:arc4random_uniform(256)/255.0 alpha:1];
    return cell;
}

//设置头部
-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    if ([kind  isEqualToString:UICollectionElementKindSectionHeader]) {  //header
        TYHeaderFooterView *header = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header" forIndexPath:indexPath];
        header.backgroundColor = [UIColor redColor];
        return header;
    }else if([kind isEqualToString:UICollectionElementKindSectionFooter]){  //footer
        TYHeaderFooterView *footer = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footer" forIndexPath:indexPath];
        footer.backgroundColor = [UIColor blueColor];
        return footer;
    }
    return [UICollectionReusableView new];
}

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section{
    return CGSizeMake(SCREEN_WIDTH, 44);
}

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section{
    return CGSizeMake(SCREEN_WIDTH, 44);
}