UICollectionview 单元格选择

Question

我已经制作了一个图像网格，为了显示它的选择，我在选择时为图像绘制了边框。但问题是当我在顶部选择一些图像并向下滚动图像网格时，底部的一些其他图像似乎也被选中了。下面是我的代码sn-p：

UINib *cellNib = [UINib nibWithNibName:@"collectionCell" bundle:nil];
[self.collectionView registerNib:cellNib forCellWithReuseIdentifier:@"cellCV"];

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setItemSize:CGSizeMake(95, 95)];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];

[self.collectionView setCollectionViewLayout:flowLayout];

以上已添加到 viewDidLoad 中，并在 nib 中设计了集合视图单元格。

并实现了以下委托：

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{   
selectedImageIndex = indexPath.row;
[collectionView reloadData]; 
}

-(CollectionCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UIImage *img = [imageArray objectAtIndex:indexPath.row];

static NSString *cellIdentifier = @"cellCV";
CollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:   
cellIdentifier forIndexPath:indexPath];
cell.imageView.image = img;
cell.imageView.tag = indexPath.row;
UIImageView *imgView = (UIImageView *)[cell viewWithTag:indexPath.row];
if (indexPath.row == selectedImageIndex) {
    imgView.layer.borderWidth =  4.0;
    imgView.layer.borderColor = [UIColor redColor].CGColor;
    NSLog(@"selected indexpath: %d", indexPath.row);
}
else {
    imgView.layer.borderWidth =  0.0;
    imgView.layer.borderColor = nil;
}
return cell;    
}

我可以猜到重用单元格出了点问题，但不确定也想不出解决问题的想法。 等待任何形式的帮助和建议。

提前致谢。

Answer 1

我不明白为什么会发生这种情况。我不认为问题在于使用row 与item，尽管您确实应该使用item。不过，我可以想象，如果您的收藏视图有多个 section，那么只查看 row/item 而忽略 section 将是一个问题（即它会选择相同的 item 数字每个 section)。

要快刀斩乱麻，我建议保存所选项目的NSIndexPath，然后将其用作比较的基础。这也使得在didSelectItemAtIndexPath 中进行优化变得容易。无论如何，首先定义你的属性：

@property (nonatomic, strong) NSIndexPath *selectedItemIndexPath;

然后实现cellForItemAtIndexPath和didSelectItemAtIndexPath：

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *cellIdentifier = @"Cell";

    CollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];

    cell.imageView.image = ...

    if (self.selectedItemIndexPath != nil && [indexPath compare:self.selectedItemIndexPath] == NSOrderedSame) {
        cell.imageView.layer.borderColor = [[UIColor redColor] CGColor];
        cell.imageView.layer.borderWidth = 4.0;
    } else {
        cell.imageView.layer.borderColor = nil;
        cell.imageView.layer.borderWidth = 0.0;
    }

    return cell;
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    // always reload the selected cell, so we will add the border to that cell

    NSMutableArray *indexPaths = [NSMutableArray arrayWithObject:indexPath];

    if (self.selectedItemIndexPath)
    {
        // if we had a previously selected cell

        if ([indexPath compare:self.selectedItemIndexPath] == NSOrderedSame)
        {
            // if it's the same as the one we just tapped on, then we're unselecting it

            self.selectedItemIndexPath = nil;
        }
        else
        {
            // if it's different, then add that old one to our list of cells to reload, and
            // save the currently selected indexPath

            [indexPaths addObject:self.selectedItemIndexPath];
            self.selectedItemIndexPath = indexPath;
        }
    }
    else
    {
        // else, we didn't have previously selected cell, so we only need to save this indexPath for future reference

        self.selectedItemIndexPath = indexPath;
    }

    // and now only reload only the cells that need updating

    [collectionView reloadItemsAtIndexPaths:indexPaths];
}

顺便说一句，请注意我并没有搞乱tag 属性（我认为没有任何价值）。另请注意，我不是重新加载整个集合视图，而是仅重新加载选定的单元格（如果以前有一个选定的单元格，那也是），这应该更有效。

Answer 2

这段代码在 Swift 3 中：

if self.selectedItemIndexPath != nil && indexPath.compare(self.selectedItemIndexPath) == .orderedSame {
    cell.imageView!.layer.borderColor = UIColor.red.cgColor
    cell.imageView!.layer.borderWidth = 4.0
} else {
    cell.imageView!.layer.borderColor = nil
    cell.imageView!.layer.borderWidth = 0.0
}

return cell