请写一个OC瀑布流列表

以下是一个简单的OC瀑布流列表的实现：

首先，我们需要导入UICollectionView和UICollectionViewFlowLayout：

#import <UIKit/UIKit.h>

@interface WaterfallViewController : UIViewController<UICollectionViewDataSource, UICollectionViewDelegate>

@end

接下来，在ViewController中实现UICollectionViewDataSource和UICollectionViewDelegate协议：

@interface WaterfallViewController ()<UICollectionViewDataSource, UICollectionViewDelegate>

@property (nonatomic, strong) UICollectionView *collectionView;
@property (nonatomic, strong) NSMutableArray *dataList;

@end

@implementation WaterfallViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];

    [self.view addSubview:self.collectionView];

    [self loadData];
}

- (void)loadData {
    // 模拟数据
    self.dataList = [NSMutableArray arrayWithObjects:@(200), @(150), @(180), @(220), @(250), @(190), @(170), @(240), @(160), @(200), @(150), @(180), @(220), @(250), @(190), @(170), @(240), @(160), nil];
}

#pragma mark - UICollectionViewDataSource

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return self.dataList.count;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *cellIdentifier = @"cellIdentifier";
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];

    cell.backgroundColor = [UIColor grayColor];

    // 设置高度
    CGFloat height = [self.dataList[indexPath.row] floatValue];
    cell.frame = CGRectMake(cell.frame.origin.x, cell.frame.origin.y, cell.frame.size.width, height);

    return cell;
}

#pragma mark - UICollectionViewDelegate

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"Selected item at index %ld", (long)indexPath.row);
}

#pragma mark - Lazy Load

- (UICollectionView *)collectionView {
    if (!_collectionView) {
        UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
        layout.minimumLineSpacing = 10;
        layout.minimumInteritemSpacing = 10;
        layout.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);

        CGFloat width = (self.view.frame.size.width - 30) / 2;
        layout.itemSize = CGSizeMake(width, 0);

        _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
        _collectionView.backgroundColor = [UIColor whiteColor];
        _collectionView.dataSource = self;
        _collectionView.delegate = self;
        [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
    }
    return _collectionView;
}

@end

这里我们模拟了一个简单的数据源数组dataList，包含了一些高度数据。在UICollectionViewDataSource代理方法中，我们根据对应的高度数据设置了每个cell的高度，实现了瀑布流效果。

另外，我们通过UICollectionViewFlowLayout设置了UICollectionView的布局方式，包括行间距、列间距、边距和每个cell的大小等。

最后，我们将UICollectionView注册到了ViewController中，并在viewDidLoad方法中加载数据源和UICollectionView。