- (UICollectionView *)collectionView{
    if (_collectionView == nil) {
        
        UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
        
        flowLayout.headerReferenceSize = CGSizeMake(fDeviceWidth, AD_height+10);//头部大小
        
        _collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, fDeviceWidth, fDeviceHeight) collectionViewLayout:flowLayout];
        
        //定义每个UICollectionView 的大小
        flowLayout.itemSize = CGSizeMake((fDeviceWidth-20)/2, (fDeviceWidth-20)/2+50);
        //定义每个UICollectionView 横向的间距
        flowLayout.minimumLineSpacing = 5;
        //定义每个UICollectionView 纵向的间距
        flowLayout.minimumInteritemSpacing = 0;
        //定义每个UICollectionView 的边距距
        flowLayout.sectionInset = UIEdgeInsetsMake(0, 5, 5, 5);//上左下右
        
        //注册cell和ReusableView（相当于头部）
        [_collectionView registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:@"cell"];
        [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"ReusableView"];
        
        //设置代理
        _collectionView.delegate = self;
        _collectionView.dataSource = self;
        
        //背景颜色
        _collectionView.backgroundColor = [UIColor whiteColor];
        //自适应大小
        _collectionView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        
    }
    return _collectionView;
}

#pragma mark 定义展示的UICollectionViewCell的个数
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 30;
}

#pragma mark 定义展示的Section的个数
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 1;
}

#pragma mark 每个UICollectionView展示的内容
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *identify = @"cell";
    CollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identify forIndexPath:indexPath];
    [cell sizeToFit];
    
    cell.imgView.image = [UIImage imageNamed:@"cat.png"];
    cell.text.text = [NSString stringWithFormat:@"Cell %ld",indexPath.item];
    
    return cell;
}

#pragma mark 头部显示的内容
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
    
    UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:
                                            UICollectionElementKindSectionHeader withReuseIdentifier:@"ReusableView" forIndexPath:indexPath];
    
    [headerView addSubview:_headerView];//头部广告栏
    return headerView;
}

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@"选择%ld",indexPath.item);
}