UICollectionview單元格選擇

Question

我制作了一個圖像網格，為了顯示其選擇，我在選擇時為圖像繪制了邊框。 但問題是當我在頂部選擇一些圖像並向下滾動圖像網格時，底部的其他一些圖像似乎也被選中。 下面是我的代碼片段：

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，其中集合視圖單元格設計為nib。

並實施以下代表：

-(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;    
}

我可以猜到重復使用單元格會出現問題，但不確定並且無法解決問題。 等待任何形式的幫助和建議。

提前致謝。

Answer 1

我不明白為什么會發生這種情況。 我不相信問題是使用row與item ，雖然你真的應該使用item 。 但是，我可以想象，如果你的集合視圖有多個section ，那么僅查看row / item但忽略section將是一個問題（即它將在每個 section選擇相同的item編號）。

為了減少Gordian結，我建議保存所選項目的NSIndexPath ，然后使用它作為比較的基礎。 這也使得在didSelectItemAtIndexPath呈現優化變得容易。 無論如何，首先定義你的財產：

@property (nonatomic, strong) NSIndexPath *selectedItemIndexPath;

然后實現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];
}

順便說一句，請注意我並沒有搞亂tag屬性（我認為沒有價值）。 另請注意，我不是重新加載整個集合視圖，而是僅重新加載所選單元格（如果還有一個先前選定的單元格，那也應該更高效）。

Answer 2

這段代碼在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