Ios Objective-C错误：使用NSArray的单元格上的IndexPath错误

我通过Swift Bridgeting在我的代码中使用CollectionView

目标C（不工作） 我的问题是IndexPath返回错误的

项

索引。以下是最低限度的代码：

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.collectionViewEvents.collectionViewLayout = [[CardsCollectionViewLayout alloc] init];
    self.collectionViewEvents.dataSource = self;
    self.collectionViewEvents.delegate = self;
    self.collectionViewEvents.pagingEnabled = YES;
    self.collectionViewEvents.showsHorizontalScrollIndicator = NO;

    [self load];
}

// Issue visible here, the indexPath.item is not correct
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    for (UICollectionViewCell *cell in self.collectionViewEvents.visibleCells) {
        NSIndexPath *indexPath = [[self collectionViewEvents] indexPathForCell:cell];
        NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
        return;
    }
}

- (void)load
{

    // self.eventData is declares as: @property (nonatomic) NSArray *eventData;
    self.eventData = [[NSArray alloc] initWithObjects:UIColor.blackColor, UIColor.whiteColor, UIColor.brownColor, nil];
    [[self collectionViewEvents] reloadData];
}

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

    cell.layer.cornerRadius = 7.0;
    cell.backgroundColor = UIColor.blackColor;

    return cell;
}

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

结果（注意第一个和第二个单元格如何具有相同的indexath项）：

---

斯威夫特（工作） 我从他的代码库中进行了尝试，它静态地声明了

colors

：

  var colors: [UIColor]  = [
    UIColor(red: 237, green: 37, blue: 78),
    UIColor(red: 249, green: 220, blue: 92),
    UIColor(red: 194, green: 234, blue: 189),
    UIColor(red: 1, green: 25, blue: 54),
    UIColor(red: 255, green: 184, blue: 209)
  ]
...

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCellReuseIdentifier", for: indexPath)

        cell.layer.cornerRadius = 7.0
        cell.backgroundColor = .black

        return cell
    }

在实现下面的代码之后，它将返回正确的indexath

    // Issue NOT visible here, the indexPath.item IS correct
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {

        for cell in collectionView.visibleCells {
            let indexPath = collectionView.indexPath(for: cell)
            print(indexPath?.item)
            return
        }
    }

结果：

2020-03-19 14:48:05.334905+0100 App[7422:2617858] Visible Cell IndexPath Item 2 # => 3rd cell
2020-03-19 14:48:05.741805+0100 App[7422:2617858] Visible Cell IndexPath Item 1 # => 2nd cell
2020-03-19 14:48:06.184932+0100 App[7422:2617858] Visible Cell IndexPath Item 0 # => 1st cell

我在我的

Objective-C

代码中做错了什么

---

我尝试过的事情

---

问题是在这个循环中有一个返回

for (UICollectionViewCell *cell in [[self collectionViewEvents] visibleCells]) {
    NSIndexPath *indexPath = [[self collectionViewEvents] indexPathForCell:cell];
    NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
    return; // <- This here
}

for（UICollectionViewCell*位于[[self-collectionViewEvents]visibleCells]中的单元格）{
nsindepath*indepath=[[self-collectionViewEvents]indexPathForCell:cell]；
NSLog（@“可见单元格indexath项%ld”，indexath.Item）；
return；//检查答案我认为您的问题是您没有将数据源设置为您的集合view@Was“Siimbenhsen为您的评论添加了澄清，并修复了Swift代码。我不想设置
backgroundColor
，而是想获得正确的
IndexPath.item
和in-Objective-C代码。您尝试过使用
[[self collectionViewEvents]indexPathsForVisibleItems]
？可能是indexPaths尚未更新的情况下，您可能需要将
for
循环排队到主队列的末尾（
dispatch\u async（dispatch\u get\u main\u queue（），^{for…}）
）.@AlejandroIván刚刚试过，检查问题的结尾。没有帮助。当你在单元格上循环时，你可以尝试打印单元格本身吗？我现在能想到的唯一解释是，当你在单元格上迭代时，可见单元格会因某种原因发生变化，但似乎不太可能。返回必须在那里。代码与Swift相同示例（我实际上希望在第一项中尽早返回）。问题在于不同卡片上的索引错误，使用相同的Objective-C和Swift代码。请参阅我再次发布的示例。
// 1st cell has index 1, instead of 0
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    for (UICollectionViewCell *cell in [[self collectionViewEvents] visibleCells]) {
        NSIndexPath *indexPath = [[self collectionViewEvents] indexPathForCell:cell];
        NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
        return;
    }

// 1st cell has index 1, instead of 0
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    NSArray *visible = [self.collectionViewEvents indexPathsForVisibleItems];
    NSIndexPath *indexPath = [visible firstObject];
    NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
    return;

// Calling it in main thread, same result
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    dispatch_async(dispatch_get_main_queue(), ^{
        for (UICollectionViewCell *cell in [[self collectionViewEvents] visibleCells]) {
            NSIndexPath *indexPath = [[self collectionViewEvents] indexPathForCell:cell];
            NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
            return;
        }
    });

for (UICollectionViewCell *cell in [[self collectionViewEvents] visibleCells]) {
    NSIndexPath *indexPath = [[self collectionViewEvents] indexPathForCell:cell];
    NSLog(@"Visible Cell IndexPath Item %ld", indexPath.item);
    return; // <- This here
}