Ios 不将图像的资源URL显示到UITableview单元格中？

嗨，我有一个包含以下资源URL的数组：

(
    "assets-library://asset/asset.JPG?id=4D80F378-FB5A-4696-B398-2C824B625CC5&ext=JPG",
    "assets-library://asset/asset.JPG?id=B727299D-3FEF-4F41-B98D-B863714356EB&ext=JPG"
)
ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
    {
        ALAssetRepresentation *rep = [myasset defaultRepresentation];
        CGImageRef iref = [rep fullResolutionImage];
        if (iref) {
            UIImage *largeimage = [UIImage imageWithCGImage:iref];
            cell.imageView.image = largeimage;
        }
    };

    ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)
    {
        NSLog(@"Can't get image - %@",[myerror localizedDescription]);
    };

    NSURL *asseturl = [arrDispImages objectAtIndex:indexPath.row];
    library = [[ALAssetsLibrary alloc] init] ;
    [library assetForURL:asseturl resultBlock:resultblock failureBlock:failureblock];

myasset is nil.
ALAssetRepresentation *rep = [myasset defaultRepresentation];
so rep is also nil.

---

我需要在UITableview中将此url显示为图像。如何显示此url？我的UITableview代码

通过抓取正确的单元格，在结果块内设置图像：

ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
{
    ALAssetRepresentation *rep = [myasset defaultRepresentation];
    CGImageRef iref = [rep fullResolutionImage];
    if (iref) {
        UIImage *largeimage = [UIImage imageWithCGImage:iref];

        NSInteger index = [arrDispImages indexOfObject:rep.url];
        UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:index inSection:0]];
        cell.imageView.image = largeimage;
    }
};

ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)
{
    NSLog(@"Can't get image - %@",[myerror localizedDescription]);
};

NSURL *asseturl = [arrDispImages objectAtIndex:indexPath.row];
library = [[ALAssetsLibrary alloc] init] ;
[library assetForURL:asseturl resultBlock:resultblock failureBlock:failureblock];

---

它在模拟器上工作，但在设备上不加载图像。因为ALAssetRepresentation*rep=[myasset defaultRepresentation]；我的资产是零