Question

我正在制作我的UIcollectionviewcell以下载图像异步但只有最后一个图像来自最后一个单元格。以下是我的代码

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

  self.collectionViewCell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

NSMutableDictionary *temperoryDictionary = [[NSMutableDictionary alloc] initWithDictionary:[self.weatherArray objectAtIndex:indexPath.row]];

NSString *imageURL = [[[temperoryDictionary valueForKey:@"weatherIconUrl"] objectAtIndex:0] valueForKey:@"value"];

 [self downloadImageWithURL:[NSURL URLWithString:imageURL] completionBlock:^(BOOL succeeded, UIImage *image) {

   if (succeeded) {

       self.collectionViewCell.weatherImage.image= image;

    }
}];

return self.collectionViewCell;
}


- (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, UIImage *image))completionBlock{


   NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

[NSURLConnection sendAsynchronousRequest:request
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
                           if (!error)
                           {
                               UIImage *imageAsync = [[UIImage alloc] initWithData:data];

                               completionBlock(YES,imageAsync);

                           } else {

                               completionBlock(NO,nil);
                           }
                       }];
}

我不知道自己犯了什么错误。

Answer 1

self.collectionViewCell只会引用一个单元格。将其替换为局部变量UICollectionViewCell * collectionViewCell

Answer 2

您不应该需要指向最后一个单元格的指针，因为它很可能是表格在图像加载完成时要求的最后一个单元格。

相反，试试这个：

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

    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];
    NSInteger currentTag = indexPath.row;
    cell.tag = currentTag;

    NSMutableDictionary *temperoryDictionary = [[NSMutableDictionary alloc] initWithDictionary:[self.weatherArray objectAtIndex:indexPath.row]];

    NSString *imageURL = [[[temperoryDictionary valueForKey:@"weatherIconUrl"] objectAtIndex:0] valueForKey:@"value"];

    __weak __typeof(cell) weakCell = cell;
    [self downloadImageWithURL:[NSURL URLWithString:imageURL] completionBlock:^(BOOL succeeded, UIImage *image) {
        if (succeeded && weakCell.tag == currentTag) {
            weakCell.weatherImage.image = image;
        }
    }];

}

这会保留指向当前单元格的弱指针，当完成加载图像时，它将检查单元格的标记（indexPath.row）是否相同，并在这种情况下设置图像。

Answer 3

而不是self.collectionViewCell，您应该使用__block UICollectionViewCell * cell：

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

        __block UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

        NSMutableDictionary *temperoryDictionary = [[NSMutableDictionary alloc] initWithDictionary:[self.weatherArray objectAtIndex:indexPath.row]];

        NSString *imageURL = [[[temperoryDictionary valueForKey:@"weatherIconUrl"] objectAtIndex:0] valueForKey:@"value"];

         [self downloadImageWithURL:[NSURL URLWithString:imageURL] completionBlock:^(BOOL succeeded, UIImage *image) {

           if (succeeded) {

               cell.weatherImage.image= image;

            }
        }];
        return cell;
    }

对于自定义单元格，请使用__block CustomClass * cell。 CustomClass是自定义单元格的类。

UICollectionViewCell中的异步映像下载？

3 个答案: