Question

我的问题是----我在UITableView中使用custom cell时在tableview中加载数据时它正在加载描述并且标题也是日期但不在tableview中加载图像。将所有图像加载到一行中。当我使用此代码时，滚动效果很好，但不能在TableView中加载图像。我想要延迟加载概念。转到下面的链接。

enter image description here

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
  static NSString *CellIdentifier = @"Cell";
  newsobject=(newscustamCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
  if (newsobject ==nil)
   {
        [[NSBundle mainBundle]loadNibNamed:@"newscustamCell" owner:self options:nil];
   }
    dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
    dispatch_async(q, ^{

         NSURL *url=[NSURL URLWithString:[NSString stringWithFormat:@"%@",[[newsarry objectAtIndex:indexPath.row] objectForKey:@"image_file"]]];

        /* Fetch the image from the server... */

        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *img = [[UIImage alloc] initWithData:data];

        dispatch_async(dispatch_get_main_queue(), ^{

            /* This is the main thread again, where we set the tableView's image to
         be what we just fetched. */

         newsobject.allnewsimg.image = img;
    // newsobject.allnewsimg.image=[UIImage imageWithData:data];

        });

    });

      newsobject.allnewsdes.text=[[[newsarry objectAtIndex:indexPath.row]            objectForKey:@"long_desc"]stringByStrippingTags];

       newsobject.allnewslabel.text=[[newsarry objectAtIndex:indexPath.row]        objectForKey:@"title"];
   ![enter image description here][1] 
        newsobject.timelabel.text=[[newsarry objectAtIndex:indexPath.row] objectForKey:@"date"];

     return newsobject;
   }

Answer 1

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
            dispatch_async(queue, ^{

                NSURL *url=[NSURL URLWithString:[NSString stringWithFormat:@"%@",[[newsarry objectAtIndex:indexPath.row] objectForKey:@"image_file"]]];

                NSData *data = [NSData dataWithContentsOfURL:url];
                UIImage *image = [UIImage imageWithData:data];

                dispatch_async(dispatch_get_main_queue(), ^{

            [tableView cellForRowAtIndexPath:indexPath].imageView.image = image;


        });
    });

Answer 2

您可以使用某些Lib，例如SDWebImage或Afnetworking。 Libs支持延迟加载图像并自动缓存此图像。所有你需要做的：

[cell.imageView setImageWithURL:[NSURL URLWithString:@"url of image"]
                   placeholderImage:nil];

Answer 3

我会与你分享一些代码。请遵循此代码。

首先，您必须从服务器检索所有数据。在tableview上加载之后。

试试这段代码：

- (void)viewDidLoad
{    
   NSString *urlString=@"http://put your url";
   self.responseData=[NSMutableData data];
   NSURLConnection *connection=[[NSURLConnection alloc]initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:urlString]] delegate:self];
   NSLog(@"connection====%@",connection);
}

JSON委托方法-------------

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
  [self.responseData setLength:0];
}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
  [self.responseData appendData:data];
}
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
  self.responseData=nil;
}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSArray *response_Array = [NSJSONSerialization JSONObjectWithData:self.responseRankData options:kNilOptions error:nil];

    NSDictionary *dataDictionary=nil;
    NSDictionary *imgurlDic=nil;
    NSArray *imgDic=nil;

   // I am retrieve image according to my url. So please edit this according to your url. i am just write the format.

    for (int i=0; i < response_Array.count; i++)
    {
        imgurlDic = [imgDic objectAtIndex:i];
        imgDic = [dataDictionary objectForKey:@"imageKey"]; // Take your Key according to URL

        NSURL *url = [NSURL URLWithString:[imgurlDic objectForKey:@"url"]];
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *img = [[UIImage alloc] initWithData:data];
        [self.Img_Array addObject:img]; // Adding all image in your image Array.

        NSLog(@"imgurlDic == %@",imgurlDic);
     }

    [self.tableview reloadData]; // reload your tableview here.
}

获取阵列中的所有图像，您可以在cellForRowAtIndexPath方法或要加载图像的位置使用此数组。

Answer 4

由于表格视图单元格快速排队/重复使用的方式，当您的网络请求完成加载时所指的单元格可能与您认为不一样（因为它已脱离屏幕并排队等待）然后重新分配给另一个indexPath）。此外，在返回单元格之前，您需要确保将其imageView的{{1}}属性重置为image或某个默认值。有关详情，请参阅我的回答：https://stackoverflow.com/a/23473911/91458

此外 - 保留已检索图像的缓存是个好主意。检查nil类，这与使用可变字典但具有内置内存管理等非常相似。

Answer 5

我也使用了这个技巧，但是线程和线程之间的索引弄得一团糟，所以我搜索了一下，我在GitHub上找到了一个很棒的库。

SDWebImage

您只需要#import <SDWebImage/UIImageView+WebCache.h>到项目中，并且只需使用以下代码即可在下载图像时定义占位符：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
        static NSString *CellIdentifier;
        CustomCell *cell = [tableview dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

        MyObject *object = (MyObject *)[self.list.array objectAtIndex:indexPath.row];

        [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                       placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

        return cell;
}

它还可以缓存下载的图像并为您提供出色的性能。

希望它会对你有所帮助！

Answer 6

我希望此链接对您有所帮助。通过使用asyn类图像加载异步...

https://github.com/nicklockwood/AsyncImageView

延迟加载tableview中的图像

6 个答案: