objective-c - 如何在 UICollectionview 自定义单元格中显示 UI Activityindicator 直到图像在服务器端下载？

Question

任何人都可以帮助我如何显示事件指示器，直到 UICollection 单元格的图像在后端下载。

在我的代码中，事件指示器仅显示最后一个单元格。不知道我在哪里犯了错误

这是我的代码:

 - (collectionCell *)collectionView:(UICollectionView *)collectionView
 cellForItemAtIndexPath:(NSIndexPath *)indexPath{

[self.menuCollectionView registerNib:[UINib nibWithNibName:@"collectionCell"
bundle:nil] forCellWithReuseIdentifier:@"CELL"];

collectionCell= [menuCollectionView dequeueReusableCellWithReuseIdentifier:@"CELL" 
                 forIndexPath:indexPath];

MenuItems *item=[itemsfinal objectAtIndex:indexPath.row];

NSMutableString *str   = [NSMutableString  stringWithFormat:@"%@", item.itemImage];

NSLog(@" url %@",str);

UIImage *image = [UIImage imageWithContentsOfFile:[self loadImage:str]];

if(image !=nil){
    collectionCell.menuRecipeImage.image = image;

    collectionCell.activityIndicator.hidden = YES;

    [collectionCell.activityIndicator stopAnimating];

}else{
    collectionCell.activityIndicator.hidden = NO;

    [collectionCell.activityIndicator startAnimating];

    collectionCell.menuRecipeImage.image = [UIImage imageNamed:@"menudefualt.png"];
}

return collectionCell;

}

Answer 1

在cellForItemAtIndexPath中，您应该设置事件指示器。然后开始在后台加载单元格的图像。加载图像后，将其应用到主线程上的单元格。

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    __block UICollectionViewCell* cell = [cv dequeueReusableCellWithReuseIdentifier:@"cell"
                                                                       forIndexPath: indexPath];

    // Placeholder text --
    UILabel* label = [[UILabel alloc] initWithFrame:cell.bounds];
    label.text = @"Downloading...";
    [cell.contentView addSubview:label];

    // Load image in background  --
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{

        NSURL* url = [NSURL URLWithString: [NSString stringWithFormat:@"http://example.com/img/img%02lu.png", (long unsigned)indexPath.row]];

        // Load and decode image --
        NSData * imageData = [NSData dataWithContentsOfURL:url];
        UIImage *image = [UIImage imageWithData:imageData];

        // Apply image on the main thread --
        dispatch_sync(dispatch_get_main_queue(), ^{
            UIImageView* iv = [[UIImageView alloc] initWithImage:image];
            [cell.contentView addSubview:iv];
        });
    });

    return cell;

}

实际示例...