我正在对 UICollectionViewCell 进行子类化，因为我想向单元格添加一个 UIImageView 和一个 UIProgressView:

- (id)initWithFrame:(CGRect)frame {

    self = [super initWithFrame:frame];
    if (self) {

        // ImageView
        _imageView = [[UIImageView alloc] initWithFrame:self.bounds];
        _imageView.layer.borderColor = [UIColor whiteColor].CGColor;
        _imageView.layer.borderWidth = 0.7;
        [self.contentView addSubview:_imageView];

        // Progress View
        _progressView = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleBar];
        _progressView.frame = CGRectMake(5, self.bounds.size.height - 20, self.bounds.size.width - 10, 10);
        _progressView.hidden = YES;
        [self.contentView addSubview:_progressView];

    }
    return self;
}

当我触摸一个单元格并调用 collectionView:didSelectItemAtIndexPath: 我设置 cell.progressView.hidden = NO; 并开始下载和更新 progressView.

但是，当我滚动时，该单元格被重用并且 progressView 显示在其他单元格上。我尝试了很多不同的方法来只在正确的单元格上显示它，但我尝试过的任何方法都不起作用。

是否有更好的方法来做到这一点，比如在 prepareForReuse 中做一些事情？

编辑:要求的完整方法

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    PUCViewpointItem *item = [self.items objectAtIndex:indexPath.row];
    PUCImageGridCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CollectionViewCellIdentifier forIndexPath:indexPath];
    [cell.imageView setImageWithURL:[NSURL URLWithString:item.imageURLHigh] placeholderImage:[UIImage imageNamed:@"PUCDefaultBackground.png"]];

    // See if we have the file already
    if (![self.itemPaths objectForKey:item.name]) {
        cell.imageView.alpha = 0.4;
    } else {
        cell.imageView.alpha = 1.0;
    }

    // See if we are downloading
    if (![self.progressItems objectForKey:item.name]) {
        cell.progressView.hidden = YES;
    } else {
        cell.progressView.hidden = NO;
    }

    return cell;
}


- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {

    PUCViewpointItem *item = [self.items objectAtIndex:indexPath.row];
    PUCImageGridCell *cell = (PUCImageGridCell *)[collectionView cellForItemAtIndexPath:indexPath];

    // File Path
    NSString *path = [self itemPath:item];
    if (!path) {

        // Set the indexPath we are downloading
        [self.progressItems setObject:indexPath forKey:item.name];

        Utility *utility = [[Utility alloc] init];
        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:item.url]];
        AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];

        NSString *localPath = [[utility localDirectory] stringByAppendingFormat:@"/%@.pdf", item.name];
        operation.outputStream = [NSOutputStream outputStreamToFileAtPath:localPath append:NO];

        [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {

            float totalProgress = (float)totalBytesRead/(float)totalBytesExpectedToRead;
            if ([[collectionView indexPathForCell:cell] isEqual:indexPath]) {
                cell.progressView.alpha = 1.0;
                cell.progressView.progress = totalProgress;
            }

        }];
        [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

            // This section seems to not get called or updated correctly when the cell 
            // that is showing the activityView is offscreen
            if ([[collectionView indexPathForCell:cell] isEqual:indexPath]) {
                [self.itemPaths setObject:localPath forKey:item.name];
                [self.progressItems removeObjectForKey:item.name];
                cell.imageView.alpha = 1.0;
                cell.progressView.alpha = 0.0;
            }

        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSLog(@"Error: %@", error);
            [self.progressItems removeObjectForKey:item.name];
            cell.progressView.alpha = 0.0;
        }];

        [operation start];

    } else {

        [self readIssueAtPath:path];

    }

}//end

最佳答案

应该存储某个项目是否正在进行下载的信息 在某些数据源(或模型)中而不是在单元格( View )中。

然后您可以根据该索引处项目的状态更新数据源委托(delegate)方法 collectionView:cellForItemAtIndexPath: 中的单元格外观 路径并显示或隐藏单元格的进度 View 。

ADDED:进度 block 、完成 block 和失败 block 都捕获当前单元格。 因此，他们将修改此单元格，即使它已被重新用于不同的索引路径。 要解决这个问题，您可以检查单元格的(当前)索引路径是否仍然相等 到原始(捕获的)索引路径:

[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {

    float totalProgress = (float)totalBytesRead/(float)totalBytesExpectedToRead;
    if ([[collectionView indexPathForCell:cell] isEqual:indexPath]) {
       cell.progressView.alpha = 1.0;
       cell.progressView.progress = totalProgress;
    }
}];

完成和失败 block 类似:

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    [self.itemPaths setObject:localPath forKey:item.name];
    [self.progressItems removeObjectForKey:item.name];
    if ([[collectionView indexPathForCell:cell] isEqual:indexPath]) {
        cell.imageView.alpha = 1.0;
        cell.progressView.alpha = 0.0;
    }

} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
    [self.progressItems removeObjectForKey:item.name];
    if ([[collectionView indexPathForCell:cell] isEqual:indexPath]) {
        cell.progressView.alpha = 0.0;
    }
}];

关于ios - 带有 UIProgressView 的自定义 UICollectionViewCell 在重复使用的单元格上显示 progressView，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16923840/