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从文档目录加载多个图像时,UICollectionView卡住

uicollectionview asynchronous objective-c ios

Monika Patel · 技术社区 · 8 年前

我正在加载超过30-50个图像,这些图像存储在文档目录中。所有图像都会立即加载到 collectionView ,但当滚动时 集合视图 到那时它会卡住的。

- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *cellIdentifier = @"ImageCell";
    ImageCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];

    //Load image from document  directory
    NSString *imageName = [arrCollection objectAtIndex:indexPath.row];
    NSString *imagePath = [NSString stringWithFormat:@"%@/%@",(AppObj).imagefolderPath, imageName];
    UIImage *localImg = [[UIImage alloc]initWithContentsOfFile:imagePath];

    cell.imgSketch.image = localImg;

    cell.txtName.text = [NSString stringWithFormat:@"%@",[imageName stringByReplacingOccurrencesOfString:@".png" withString:@""]];

    cell.layer.masksToBounds = YES;
    return cell;
}

我也试着跟踪调度组

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
                UIImage *localImg = [[UIImage alloc]initWithContentsOfFile:[NSString stringWithFormat:@"%@/%@",(AppObj).imagefolderPath,[arrCollection objectAtIndex:indexPath.row]]];
                dispatch_async(dispatch_get_main_queue(), ^{
                    cell.imgSketch.image = localImg;
                });
            });

请给我建议解决这个问题的办法。

提前谢谢

4 回复 | 直到 8 年前

Nirav D 8 年前

你可以用 SDWebImage 它还显示来自文档目录的图像。

[cell.imgSketch sd_setImageWithURL:[NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@",(AppObj).imagefolderPath,[arrCollection objectAtIndex:indexPath.row]]]];

注: 使用 fileURLWithPath 创建对象时 NSURL 因为它是文件的路径。

bseh 8 年前

我建议将图像加载操作移到后台线程。

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL), ^{
   UIImage* localImage = [[UIImage alloc] initWithContentsOfFile:[NSString stringWithFormat:@"%@/%@",(AppObj).imagefolderPath,[arrCollection objectAtIndex:indexPath.row]]];    
   dispatch_async(dispatch_get_main_queue(), ^{
      cell.imgSketch.image = localImage;
   });
});

Shehata Gamal 8 年前

我建议只加载一次所有的图像 cellForRowAt

NSMutableArray*images; // every instance is of type UIImage not imageName

而不是这个

UIImage *localImg = [[UIImage alloc]initWithContentsOfFile:[NSString stringWithFormat:@"%@/%@",(AppObj).imagefolderPath,[arrCollection objectAtIndex:indexPath.row]]];

注: 这种方法 initWithContentsOfFile 在主队列中运行,所以这是卡滞的主要原因

Lal Krishna 8 年前

如果使用大图像,collectionview/tableview单元格将闪烁。尝试使用小尺寸图像或在 cellForItemAtIndexPath 在后台队列中。

可以通过在数组中缓存图像来提高性能。 注意:如果容量增加了限制,请尝试清洁它。

cell.imgSketch.image = nil;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{

     UIImage *localImg = [[UIImage alloc] initWithContentsOfFile:[NSString stringWithFormat:@"%@/%@", (AppObj).imagefolderPath, [arrCollection objectAtIndex:indexPath.row]]];

     NSData *imgData = UIImageJPEGRepresentation(localImg, 0.5);
     localImg = [UIImage imageWithData:imgData];

     dispatch_async(dispatch_get_main_queue(), ^{
         ImageCell *imageCell = [collectionView cellForItemAtIndexPath:indexPath];
         if (imageCell) {
             cell.imgSketch.image = localImg;
         }
    });
});