iOS懒人加载表格图像 [英] iOS lazy-loading of table images

问题描述

我已经使用apple提供的示例在我的应用中成功实现了图像的延迟加载此处。问题是，我希望在我滚动时加载图像，但只有当我完成拖动时才将图像加载到单元格中（从屏幕释放我的手指。此时单元格保持为空）。我修改了代码如下：

I have successfully implemented lazy-loading of images in my app using the example provided by apple here. The thing is that, I want the image to load as I am scrolling, but the image loads into the cell only when I finish dragging (Release my finger from the screen. Until then the cell remains empty). I have modified the code as follows:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

    //NSLog(@"cell for row at indexpath, size - %f, current - %d", flowTable.contentSize.height, self.current);

    NSString *CellIdentifier = @"FlowCell";

    MyFlowCell *cell = (MyFlowCell *)[self.flowTable dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {

        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"FlowCell" owner:nil options:nil];
       // cell = [nib objectAtIndex:0];

        for(id currentObject in nib)

        {

        if([currentObject isKindOfClass:[MyFlowCell class]])

        {
            cell = (MyFlowCell *)currentObject;

            break;
        }
        }
    }

    ImageDetails *rowItem = [self.imageData objectAtIndex:indexPath.row];

    if (!rowItem.mainImage)
    {  
       // if (self.flowTable.dragging == NO && self.flowTable.decelerating == NO)
       // {

            [self startIconDownload:rowItem forIndexPath:indexPath];

        //}

        cell.mainImage.backgroundColor = [UIColor grayColor];

    }
    else
    {

            cell.mainImage.image = rowItem.mainImage;

    }
    }


    return cell;
}


- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
    if (!decelerate)
    {
      //  [self loadImagesForOnscreenRows];
    }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    //[self loadImagesForOnscreenRows];
}

此外，我发现在我的ImageDownloader类中，NSURLConnection没有甚至收到响应，直到我从屏幕上释放手指。我一直试图找出为什么会这样，但到目前为止我还没有成功。请告诉我是否遗漏了某些内容。

Moreover, I found out that in my ImageDownloader class, the NSURLConnection doesn't even receive the response until I release my finger from the screen. I have been trying to find out why this is happening, but I haven't been successful so far. Please tell me if I've been missing something.

推荐答案

您可以按照以下步骤在tableview中实现延迟加载：

You can achieve lazy loading in your tableview by following these steps :

在Class.h中，放置：

In your Class.h, put:

NSMutableDictionary *Dict_name;
BOOL isDragging_msg, isDecliring_msg;

现在在Class.m文件中，将此代码放入视图中加载：

Now In Class.m file, put this code in view did load:

Dict_name = [[NSMutableDictionary alloc] init];

在cellForRowAtIndexPath中：

In cellForRowAtIndexPath:

if ([dicImages_msg valueForKey:[[msg_array objectAtIndex:indexPath.row] valueForKey:@"image name or image link"]]) { 
    cell.image_profile.image=[dicImages_msg valueForKey:[[msg_array objectAtIndex:indexPath.row] valueForKey:@"image name or image link"]];
}
else
{
    if (!isDragging_msg && !isDecliring_msg)
    {
        [dicImages_msg setObject:[UIImage imageNamed:@"Placeholder.png"] forKey:[[msg_array objectAtIndex:indexPath.row] valueForKey:@"image name or image link"]];
        [self performSelectorInBackground:@selector(downloadImage_3:) withObject:indexPath];
    }
    else
    {
        cell.image_profile.image=[UIImage imageNamed:@"Placeholder.png"];
    }
}

对于下载图片，该功能为：

And for the download image the function is:

-(void)downloadImage_3:(NSIndexPath *)path{
    NSAutoreleasePool *pl = [[NSAutoreleasePool alloc] init];

    NSString *str=[here Your image link for download];

    UIImage *img = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:str]]]; 

    [dicImages_msg setObject:img forKey:[[msg_array objectAtIndex:path.row] valueForKey:@"image name or image link same as cell for row"]];

    [tableview performSelectorOnMainThread:@selector(reloadData) withObject:nil waitUntilDone:NO];

    [pl release];
}

最后将这些方法放入你的班级：

And at last put these methods in your class:

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
    isDragging_msg = FALSE;     
    [tableview reloadData];
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
    isDecliring_msg = FALSE;
    [tableview reloadData]; 
}
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
    isDragging_msg = TRUE;
}
- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView{
    isDecliring_msg = TRUE; 
}

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