UICollectionHeaderView

我们都知道UITableView有个ViewForHeaderInSection
然后我们在做UICollectionView的时候同样需要一个SectionHeaderView

首先需要自定义一个view

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface SSChoosePhotoHeaderView : UICollectionReusableView

@property (nonatomic, strong)UILabel* testLabel;

@end

NS_ASSUME_NONNULL_END

#import "SSChoosePhotoHeaderView.h"

@implementation SSChoosePhotoHeaderView

-(instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        UILabel* label = [[UILabel alloc] initWithFrame:CGRectMake(5, 0, KMAIN_SCREEN_WIDTH, 44)];
        _testLabel = label;
        [self addSubview:label];
    }
    return self;
}

然后呢需要在CollectionView去注册, 并实现代理方法, 重点:必须在Layout的HeaderReferenceSize里给个size

-(void)setBasicUI{
  
    CGFloat kItemWidth = (self.view.width-6)/3;
    CGFloat kItemHeight = kItemWidth;
    UICollectionViewFlowLayout *layout= [[UICollectionViewFlowLayout alloc]init];
    [layout setItemSize:CGSizeMake(kItemWidth, kItemHeight)];
    //    [layout setSectionInset:UIEdgeInsetsMake(2, 2, 2 ,2)];
    [layout setSectionInset:UIEdgeInsetsMake(1, 1, 1 , 1)];
    layout.headerReferenceSize = CGSizeMake(KMAIN_SCREEN_WIDTH, 44);

    
    self.collectionView = [[UICollectionView alloc]initWithFrame:(CGRect){0, 0, self.view.width, self.view.height} collectionViewLayout:layout];
    self.collectionView.backgroundColor = [UIColor whiteColor];
    self.collectionView.delegate=self;
    self.collectionView.dataSource=self;
    self.collectionView.alwaysBounceVertical = YES;
    [self.collectionView registerNib:[UINib nibWithNibName:NSStringFromClass([SSChoosePhotoCollectionViewCell class]) bundle:nil] forCellWithReuseIdentifier:NSStringFromClass([SSChoosePhotoCollectionViewCell class])];
    [self.view addSubview:self.collectionView];
    [self.collectionView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.mas_equalTo(self.naviBar.mas_bottom);
        make.left.right.bottom.equalTo(self.view);
    }];
     [_collectionView registerClass:[SSChoosePhotoHeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:NSStringFromClass([SSChoosePhotoHeaderView class])];
    if ([self.collectionView respondsToSelector:@selector(setPrefetchingEnabled:)]) {
        self.collectionView.prefetchingEnabled = false;
    }
    //    [self.collectionView reloadData];
}

-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        SSChoosePhotoHeaderView* view = [_collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:NSStringFromClass([SSChoosePhotoHeaderView class]) forIndexPath:indexPath];
        if (view == nil) {
            view = [[SSChoosePhotoHeaderView alloc] initWithFrame:CGRectMake(0, 0, KMAIN_SCREEN_WIDTH, 44)];
        }
        JSDateModel* model = _itemsArray[indexPath.section];
        view.testLabel.text = model.dateString;
        return view;
    }
    return nil;
    
}

接下来就是如果headsize有所变化的话就必须实现代理方法UICollectionViewDelegateFlowLayout

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;//item尺寸
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;//section Inset
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section;//行间距
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;//列间距
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section;//head size
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section;//footer size