UICollectionView的基础应用

@interface ViewController ()
设置遵从的代理


@property (nonatomic,strong)UICollectionViewFlowLayout *flowLayout;
@property (nonatomic,strong)UICollectionView *collectionView;
@end

1.UICollectionViewDelegateFlowLayout 代理方法

设置item大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.section==0) {
        return CGSizeMake(100, 100);
    }
    return CGSizeMake(90, 90);
}
设置边缘约束---上、下、左、右
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    if (section==0) {
        return UIEdgeInsetsMake(10, 75/4, 10, 75/4);
    }
    return UIEdgeInsetsMake(10, 105/4, 10, 105/4);
}
增广头视图大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
    return CGSizeMake(0, 50);
}
增广尾视图大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
{
    return CGSizeMake(0, 30);
}

2.集合视图布局

 ①布局必须借助UICollectionViewFlowLayout布局类完成, UICollectionViewFlowLayout为公共类, 一般采用其子类UICollectionViewFlowLayout完成布局任务
 ②集合视图默认背景颜色为穿透色(黑色), 必须手动设置其背景颜色
 ③每行item的个数多少由多因素影响, 不能人为规定(sectionInset、itemSize、minimumLineSpacing)
 ④增广视图也具有代理方法, 必须存在重用机制(需注册, 可重用, 可自定义)
 ⑤集合视图的Cell、item子控件只有一层view,实现多功能布局必须自定义

- (void)layoutCollectionView
{
    self.flowLayout = [[UICollectionViewFlowLayout alloc]init];
    // 属性
    //item大小
    _flowLayout.itemSize = CGSizeMake(100, 100);
    // 最小列间距
    _flowLayout.minimumInteritemSpacing = 75/4.f;
    // 最小行间距
    _flowLayout.minimumLineSpacing = 10.f;
    // 分区内容边间距
    _flowLayout.sectionInset = UIEdgeInsetsMake(10, 75/4, 10, 75/4);
    // 增广头视图尺寸
    _flowLayout.headerReferenceSize = CGSizeMake(30, 30);
    // 增广尾视图尺寸
    _flowLayout.footerReferenceSize = CGSizeMake(50, 50);
    // 滑动方向
    _flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;
}

// 创建集合视图CollectionView
- (void)creatCollectionView
{
    self.collectionView = [[UICollectionView alloc]initWithFrame:[UIScreen mainScreen].bounds collectionViewLayout:_flowLayout];
    _collectionView.delegate = self;
    _collectionView.dataSource = self;
    // 设置背景颜色
    _collectionView.backgroundColor = [UIColor cyanColor];
    // 注册Cell/item
//    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"CollectionCell"];
    [_collectionView registerNib:[UINib nibWithNibName:@"ApCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"ApCollectionViewCell"];
    
    
    // 注册增广头视图
//    [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"];
    [_collectionView registerNib:[UINib nibWithNibName:@"ApReusableView" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"ApReusableView"];
    
    // 注册增广尾视图
    [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"FooterView"];
     self.view = _collectionView;
}

3.collectionView相关代理

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    if (section==0) {
        return 9;
    }else{
        return 21;
    }
    
//    return 100;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
//    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"CollectionCell" forIndexPath:indexPath];
     ApCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"ApCollectionViewCell" forIndexPath:indexPath];
    cell.backgroundColor =[UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0  blue:arc4random()%256/255.0  alpha:1.f];
    return cell;
}

// 增广视图代理方法
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
//        UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
        
        ApReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"ApReusableView" forIndexPath:indexPath];
        headerView.backgroundColor = [UIColor redColor];
        return headerView;
    }else{
        UICollectionReusableView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"FooterView" forIndexPath:indexPath];
        footerView.backgroundColor = [UIColor greenColor];
        return footerView;
    }
}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 2;
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@"第%ld分区，第%ld个Item",indexPath.section+1,indexPath.row+1);
}