在tableview中异步设置图像 [英] Asynchronously set images in tableview

问题描述

我使用自定义单元格 TableView 。我最初设置从 cellForRowAtIndexPath 方法中的URL抓取图像

I have a TableView using custom cells. I initially was setting grabbing an image from a URL in the cellForRowAtIndexPath method

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *simpleTableIdentifier = @"SimpleTableCell";

    SimpleTableCell *cell = (SimpleTableCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
    if (cell == nil)
    {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"SimpleTableCell" owner:self options:nil];
        cell = [nib objectAtIndex:0];
    }

    NSDictionary *dictObject = [places objectAtIndex:indexPath.row];
    cell.nameLabel.text  = [dictObject valueForKey:@"PlaceTitle"];

    NSURL *url = [NSURL URLWithString:@"http://images1.fanpop.com/images/image_uploads/Mario-Kart-Wii-Items-mario-kart-1116309_600_600.jpg"];
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *image = [UIImage imageWithData:data];
    cell.thumbnailImageView.image = image;

    return cell;
}

但这使我的TableView滚动滞后。一旦我删除了图像提取，它滚动得很好，所以我知道这是我的问题。

but this was making my TableView scroll laggy. Once I removed the image fetch, it scrolled fine, so I know this is my problem.

我的问题是：如何异步获取此图像并将其设置在我的图像中细胞？是否有捷径可寻？谢谢！

My question is: how can I asynchronously fetch this image and set it in my cell? Is there an easy way to do this? Thanks!

推荐答案

步骤1：拥有包含图像的缓存。要么只是在内存中，要么在磁盘上更好。

Step 1: Have a cache containing images. Either just in memory, better on disk.

步骤2：当您需要图像时，调用一个方法，该方法从缓存中返回图像，或返回默认图像并开始下载。

Step 2: When you need an image, call a method which either returns an image from the cache, or returns a default image and starts a download.

步骤3：下载完成后，将图像添加到缓存中。然后找出哪些行需要图像。重新加载重新加载图像的所有行。

Step 3: When a download finishes, add the image to the cache. Then find out which rows need the image. Reload all the rows that reload the image.

下载应该使用GCD异步完成。我真的建议您将下载代码添加到单独的可重用方法中，以便您可以处理下载错误。即使你现在不这样做，你也会在以后再做。

The download should be done asynchronously using GCD. I would really recommend that you add the download code into a separate, reusable method so that you can handle download errors. Even if you don't do it now, you will do it later.

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