UICollectionview单元格选择 [英] UICollectionview cell selection

问题描述

我制作了一个图像网格，为了显示其选择，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，底部的其他一些图像似乎也被选中。下面是我的代码片段：

i have made a grid of images and in order to show its selection i drew border for the image when selected. but the problem is when i select some image at the top and scroll down the grid of images, some other image at the bottom also seemed to be selected. below is my code snippet:

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];

上面已添加到viewDidLoad中，其中集合视图单元格为nib设计。

Above has been added in viewDidLoad with the collection view cell designed in nib.

并在代表之后实现：

-(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;    
}

我可以猜到重复使用单元格出了问题，但不确定并且无法解决它的想法。
等待任何形式的帮助和建议。

i could guess that something is going wrong with reusing the cell, but not sure and couldnt het an idea to resolve it. Waiting for any kind of help and suggestions.

提前致谢。

推荐答案

我不明白为什么会这样。我不相信问题是使用行 vs item ，尽管你真的应该使用项目。但是，我可以想象，如果您的集合视图有多个部分，那只能查看行 / item 但是忽略部分会有问题（即它会选择相同的项目 每个 部分中的数字）。

I'm not seeing why this would take place. I do not believe the issue is the use of row vs item, though you really should use item. I can imagine, though, if your collection view has more than one section, that only looking at row/item but ignoring section would be a problem (i.e. it would select the same item number in every section).

要削减戈尔迪结，我建议保存所选项目的 NSIndexPath ，然后使用它作为比较的基础。这也使得在 didSelectItemAtIndexPath 中呈现优化变得容易。无论如何，首先定义你的属性：

To cut the Gordian knot, I'd suggest saving the NSIndexPath of the selected item, and then using that for the basis of comparison. That also makes it easy to render an optimization in didSelectItemAtIndexPath. Anyway, first define your property:

@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 property（我看不到任何值）。另请注意，我不是重新加载整个集合视图，而是仅重新加载所选单元格（如果还有一个先前选定的单元格，那也应该更高效）。

As an aside, note that I'm not messing around with the tag property (I see no value in that). Also note that rather than reloading entire collection view, I'm only reloading the selected cell (and if there was a previous selected cell, that one too), which should be more efficient.

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