123.png
先分析一下结构，整体是UICollectionView， 在UICollectionView头部嵌套一个UICollectionView，详细内容如图所示：
12.png
先创建一个UICollectionView, UICollectionView的顶部偏移120高度，来做为UICollectionView的头部试图，在头部添加一个UICollectionView。
UICollectionViewFlowLayout * fl = [[UICollectionViewFlowLayout alloc]init];
fl.scrollDirection = UICollectionViewScrollDirectionVertical;
_collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, GFMainScreenHeight) collectionViewLayout:fl];
fl.sectionInset = UIEdgeInsetsMake(0, 0, 0, 0);
fl.minimumLineSpacing = 0;
fl.minimumInteritemSpacing= 0;
fl.itemSize = CGSizeMake(GFMainScreenWidth/2, 30);
_collectionView.backgroundColor=[UIColor whiteColor];
_collectionView.delegate = self;
_collectionView.dataSource = self;
//顶部偏移120
_collectionView.contentInset = UIEdgeInsetsMake(120, 0, 0, 0);
//_collectionView 宽高自动
_collectionView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
[_collectionView registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
[_collectionView registerClass:[TitleCollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"collectionCellIndentider"];
[self.view addSubview:_collectionView];
//头部
// 注意这里设置headerView的头视图的y坐标一定是从"负值"开始,因为headerView是添加在collectionView上的.
UIView *headerView = [[UIView alloc]initWithFrame:CGRectMake(0, -120, self.view.frame.size.width, 120)];
headerView.backgroundColor = [UIColor greenColor];
UICollectionViewFlowLayout * fl2 = [[UICollectionViewFlowLayout alloc]init];
fl2.scrollDirection = UICollectionViewScrollDirectionVertical;
_headCollectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, 120) collectionViewLayout:fl2];
fl2.sectionInset = UIEdgeInsetsMake(0, 0, 0, 0);
fl2.minimumLineSpacing = 0;
fl2.minimumInteritemSpacing= 0;
fl2.itemSize = CGSizeMake(GFMainScreenWidth/2, 30);
_headCollectionView.backgroundColor=[UIColor whiteColor];
_headCollectionView.delegate = self;
_headCollectionView.dataSource = self;
[_headCollectionView registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:@"cellIdentifierTwo"];
[headerView addSubview:_headCollectionView];
[_collectionView addSubview:headerView];
实现UICollectionViewDataSource、UICollectionViewDelegate
确定有几个区域，先判断是哪一个UICollectionView， 如果是头部UICollectionView，区数为1，如果是_collectionView，区数是3；
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
if (collectionView == _collectionView) {
return 3;
}else{
return 1;
}
return 0;
}
确定每个区有多少行，先判断是哪一个UICollectionView， 如果是头部UICollectionView，行数为_titleArray.count； 如果是_collectionView，先判断下拉列表是否打开，如果是打开的行数为 _productTitleArray.count，如果不打开行数就为0；
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
if (collectionView == _collectionView) {
if ([_isExpandArray[section]isEqualToString:@"1"]) {
return _productTitleArray.count;
}else{
return 0;
}
}else{
return _titleArray.count;
}
return 0;
}
添加区头内容，使用区头首先需要注册TitleCollectionReusableView，上面我已经注册过了，如果没有注册，区头就会不出来。这里加了一个一个判断，主要是将区头添加到_collectionView，如果不加判断我们的头部试图也会有区头。
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
UICollectionReusableView *reusableview = nil;
if (collectionView == _collectionView) {
TitleCollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"collectionCellIndentider" forIndexPath:indexPath];
headerView.backgroundColor = [UIColor whiteColor];
reusableview = headerView;
if ([_isExpandArray[indexPath.section] isEqualToString:@"0"]) {
//未展开
headerView.selectImageView.image = [UIImage imageNamed:@"off"];
}else{
//展开
headerView.selectImageView.image = [UIImage imageNamed:@"open"];
}
headerView.provinceLabel.text = [NSString stringWithFormat:@"商品%ld", (long)indexPath.section];
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapAction:)];
tap.delegate = self;
headerView.tag = indexPath.section;
[headerView addGestureRecognizer:tap];
}
return reusableview;
}
区头的大小设置,要判断一个加大小添加到有区头的UICollectionView上去，要不然会崩溃的
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section {
if (collectionView == _collectionView) {
return CGSizeMake(GFMainScreenWidth, 40);
}else{
return CGSizeMake(GFMainScreenWidth, 0);
}
}
加载cell， 判断不同的UICollectionView，加载不同样式、内容的cell
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
if (collectionView == _headCollectionView) {
CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifierTwo" forIndexPath:indexPath];
cell.titleLable.text = _titleArray[indexPath.row];
cell.detailLable.text = _detailArray[indexPath.row];
switch (indexPath.row) {
case 0:case 1:case 4:case 5:case 8:case 9:case 12:case 13:case 16:case 17:case 20:case 21:
cell.backgroundColor = [UIColor colorWithRed:230.0/255.0 green:230.0/255.0 blue:230.0/255.0 alpha:1.0];
break;
case 2:case 3:case 6:case 7:case 10:case 11:case 14:case 15:case 18:case 19:case 22:case 23:
cell.backgroundColor = [UIColor whiteColor];
break;
default:
break;
}
return cell;
}else{
CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath];
cell.titleLable.text = _productTitleArray[indexPath.row];
cell.detailLable.text = _productDetailArray[indexPath.row];
return cell;
}
return nil;
}
添加区头的点击下拉或者关闭方法，现将开关数组的属性调整，然后刷新当前区域的内容
- (void)tapAction:(UITapGestureRecognizer *)tap{
if ([_isExpandArray[tap.view.tag] isEqualToString:@"0"]) {
//关闭 => 展开
[_isExpandArray removeObjectAtIndex:tap.view.tag];
[_isExpandArray insertObject:@"1" atIndex:tap.view.tag];
}else{
//展开 => 关闭
[_isExpandArray removeObjectAtIndex:tap.view.tag];
[_isExpandArray insertObject:@"0" atIndex:tap.view.tag];
}
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:tap.view.tag];
NSRange rang = NSMakeRange(indexPath.section, 1);
NSIndexSet *set = [NSIndexSet indexSetWithIndexesInRange:rang];
[_collectionView reloadSections:set];
}
最后效果：
Simulator Screen Shot 2017年9月12日 下午5.22.50.png
