GCD UITableView异步加载图像，加载错误的单元格直到新图像下载

发布于 2024-12-11 00:24:23 字数 1177 浏览 0 评论 0原文

我有一个带有自定义单元格的 UITableView。我使用 Grand Central Dispatch 异步加载图像。一切正常，但是当我向下滚动时，会显示以前加载的图像，直到下载新图像为止。这是我的代码：

if (![[NSFileManager defaultManager] fileExistsAtPath:[path stringByAppendingPathComponent:@"image.png"]])
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,  0ul);
    dispatch_async(queue, ^{
        NSString *url=[pat stringByAppendingPathComponent:@"comments.txt"];
        NSString *u=[NSString stringWithContentsOfFile:url encoding:NSUTF8StringEncoding error:nil];
        NSURL *imageURL=[NSURL URLWithString:u];
        NSData *image=[NSData dataWithContentsOfURL:imageURL];
        [image writeToFile:[pat stringByAppendingPathComponent:@"image.png"] atomically:YES];
        dispatch_sync(dispatch_get_main_queue(), ^{
            cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
            [cell setNeedsLayout];
            NSLog(@"Download");
        });
    });
}
else
{
    NSLog(@"cache");
    cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
}

任何建议表示赞赏。 PS我重复使用细胞

原文

I have a UITableView with custom cells. I load images asynchronously using Grand Central Dispatch. Everything works fine, but when I scroll down, previously loaded images are shown till the new image is downloaded. Here is my code:

if (![[NSFileManager defaultManager] fileExistsAtPath:[path stringByAppendingPathComponent:@"image.png"]])
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,  0ul);
    dispatch_async(queue, ^{
        NSString *url=[pat stringByAppendingPathComponent:@"comments.txt"];
        NSString *u=[NSString stringWithContentsOfFile:url encoding:NSUTF8StringEncoding error:nil];
        NSURL *imageURL=[NSURL URLWithString:u];
        NSData *image=[NSData dataWithContentsOfURL:imageURL];
        [image writeToFile:[pat stringByAppendingPathComponent:@"image.png"] atomically:YES];
        dispatch_sync(dispatch_get_main_queue(), ^{
            cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
            [cell setNeedsLayout];
            NSLog(@"Download");
        });
    });
}
else
{
    NSLog(@"cache");
    cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
}

Any suggestions appreciated.
P.S. I reuse the cells

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孤云独去闲 2024-12-18 00:24:23

您不需要捕获单元格，而是需要捕获索引路径，然后使用以下方法取回单元格：

UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

这样，如果单元格现在不在屏幕上，您将返回 nil，并且图像不会设置在错误的单元格上。

您需要在 dispatch_async() 之后添加的另一件事是 cell.imageView.image=somePlaceholderImage。

例如：

if (![[NSFileManager defaultManager] fileExistsAtPath:[path stringByAppendingPathComponent:@"image.png"]])
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,  0ul);
    dispatch_async(queue, ^{
        NSString *url=[pat stringByAppendingPathComponent:@"comments.txt"];
        NSString *u=[NSString stringWithContentsOfFile:url encoding:NSUTF8StringEncoding error:nil];
        NSURL *imageURL=[NSURL URLWithString:u];
        NSData *image=[NSData dataWithContentsOfURL:imageURL];
        [image writeToFile:[pat stringByAppendingPathComponent:@"image.png"] atomically:YES];
        dispatch_sync(dispatch_get_main_queue(), ^{
            UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
            cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
            [cell setNeedsLayout];
            NSLog(@"Download");
        });
    });
    cell.imageView.image=[UIImage imageNamed:@"placeholder"];
}
else
{
    NSLog(@"cache");
    cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
}

Rather than capturing the cell you need to capture the index path, then get the cell back using:

UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

That way, if the cell is now off screen you'll get nil back and the image won't be set on the wrong cell.

The other thing you need to add after your dispatch_async() is a cell.imageView.image=somePlaceholderImage.

E.g.:

if (![[NSFileManager defaultManager] fileExistsAtPath:[path stringByAppendingPathComponent:@"image.png"]])
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,  0ul);
    dispatch_async(queue, ^{
        NSString *url=[pat stringByAppendingPathComponent:@"comments.txt"];
        NSString *u=[NSString stringWithContentsOfFile:url encoding:NSUTF8StringEncoding error:nil];
        NSURL *imageURL=[NSURL URLWithString:u];
        NSData *image=[NSData dataWithContentsOfURL:imageURL];
        [image writeToFile:[pat stringByAppendingPathComponent:@"image.png"] atomically:YES];
        dispatch_sync(dispatch_get_main_queue(), ^{
            UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
            cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
            [cell setNeedsLayout];
            NSLog(@"Download");
        });
    });
    cell.imageView.image=[UIImage imageNamed:@"placeholder"];
}
else
{
    NSLog(@"cache");
    cell.imageView.image=[UIImage imageWithContentsOfFile:[pat stringByAppendingPathComponent:@"image.png"]];
}

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鸢与 2024-12-18 00:24:23

在您的 - (void)tableView:(UITableView *)aTableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath { 中，您需要清除图像，或将其重置为微调器。由于表视图行被重用，这就是您将看到的行为。

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