Question

I use apple’s code IconDownloader to download the image,I have added the IconDownloader file,but it doesn’t work.

- (void)startIconDownload:(UserInfo *)userImageObject forIndexPath:(NSIndexPath *)indexPath
{
    IconDownLoader *iconDownloader = [imageDownloadsInProgress objectForKey:indexPath];
    if (iconDownloader == nil) 
    {
        iconDownloader = [[IconDownLoader alloc] init];
        iconDownloader.appRecord = userImageObject;
        iconDownloader.indexPathInTableView = indexPath;
        iconDownloader.delegate = self;
        [imageDownloadsInProgress setObject:iconDownloader forKey:indexPath];
        NSLog(@"indexPath:%@",indexPath);
        NSLog(@"iconDownloader:%@",iconDownloader);
        NSLog(@"imageDownloadsInProgress:%@",[imageDownloadsInProgress objectForKey:indexPath]);
        [iconDownloader startDownload];
        [iconDownloader release];
    }

}
// called by our ImageDownloader when an icon is ready to be displayed
- (void)appImageDidLoad:(NSIndexPath *)indexPath
{
    IconDownLoader *iconDownloader = [imageDownloadsInProgress objectForKey:indexPath];
    NSLog(@"%@",imageDownloadsInProgress);
    if (iconDownloader != nil)
    {
        UITableViewCell *cell = [myTableView cellForRowAtIndexPath:iconDownloader.indexPathInTableView];

        // Display the newly loaded image
        cell.imageView.image = iconDownloader.appRecord.image;

    }
}

this is my log:

1970-01-13 14:44:32.-714 Mo[5726:307] indexPath:<NSIndexPath 0x275260> 2 indexes [0, 0]
1970-01-13 14:44:32.-694 Mo[5726:307] iconDownloader:<IconDownLoaderTan: 0x2c57a0>
1970-01-13 14:44:32.-689 Mo[5726:307] imageDownloadsInProgress:(null)

we can see the problem is imageDownloadsInProgress dictionary is null,why?but the key(indexPath) and the object(iconDownloader) are not null.who can tell me why?thanks in advance.

I have defined the imageDownloadsInProgress in my .h file:

NSMutableDictionary *imageDownloadsInProgress;  

Answer 1

two issues i think are in your code.

1) imageDownloadsInProgress might not be initialized ..
so initialize it in your vieDidLoad (can’t add objects without initializing)

imageDownloadsInProgress = [NSMutableDictionary dictionary];

2) You are setting index path as a key for the object in the dictionary…i believe you can only set NSString as a key so make a string with the index path using NSString stringWithFormat: and then store it in the dictionary