UICollectionView基本使用

1.首先创建 UICollectionViewFlowLayout对象布局。

UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc]init];
 layout.minimumLineSpacing = 5.0;
 layout.minimumInteritemSpacing = 5.0;
 layout.sectionInset = UIEdgeInsetsMake(5.0, 5.0, 5.0, 5.0);
 _myCollectionView.collectionViewLayout = layout;

2.注册collectionViewCell 和头部示图

[_myCollectionView registerNib:[UINib nibWithNibName:@"CT_MyCollectionReusableView" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"CT_MyCollectionReusableView"];
//    [_myCollectionView registerClass:[CT_MyCollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"CT_MyCollectionReusableView"];
[_myCollectionView registerNib:[UINib nibWithNibName:@"CT_MyCollectionViewCell" bundle:[NSBundle mainBundle]] forCellWithReuseIdentifier:@"myCollectionViewCell"];
_myCollectionView.dataSource = self;
_myCollectionView.delegate = self;

3.实现协议代理

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 2;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    if (section == 0) {
        return 15;
    } else if (section == 1) {
        return 12;
    } else {
       return 0;
    }
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    CT_MyCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"myCollectionViewCell" forIndexPath:indexPath];
    cell.imag.backgroundColor = [UIColor whiteColor];
    NSString *imagName ;
    if (indexPath.section == 0) {
        imagName = [NSString stringWithFormat:@"Stickers I-01-%02d",indexPath.row+1];
    } else {
        imagName = [NSString stringWithFormat:@"Stickers I-03-%02d",indexPath.row+1];
    }
    cell.imag.image = [UIImage imageNamed:imagName];
    return cell;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    CGFloat width = ((kScreenW-20)/3);
    CGSize size = CGSizeMake(width, width);
    return size;
}


- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    if (kind == UICollectionElementKindSectionHeader) {
        CT_MyCollectionReusableView *aView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"CT_MyCollectionReusableView" forIndexPath:indexPath];
        if (indexPath.section == 0) {
            aView.titleLbl.text = @"生活类贴纸展示";
        } else {
            aView.titleLbl.text = @"美食类贴纸展示";
        }
        aView.titleLbl.textColor = [UIColor whiteColor];
        return aView;
    }
    return nil;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
    if (section == 0) {
        return CGSizeMake(kScreenW, 40);
    }else{
        return CGSizeMake(kScreenW, 40);
    }
}

4.整个collectionView的头部可以通过设置contentInset实现

    UIView *head = [[UIView alloc] initWithFrame:CGRectMake(0, -300,kScreenW,300)];
    [_myCollectionView addSubview:head];
    _myCollectionView.contentInset = UIEdgeInsetsMake(300, 0, 0, 0);