Delay when refreshing UITableView custom cell - objective-c

Question

I have a UITableView with a custom cell which i fill (with array infoservices) after parsing the xml data.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
ApplicationCell *cell = (ApplicationCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
[self.cellNib instantiateWithOwner:self options:nil];
cell = tmpCell;
self.tmpCell = nil;
}
infoService *e = [self.infoservices objectAtIndex:indexPath.row];
cell.name = [e infoName];
NSString *infodetails = [e infoDetails];
if ( infodetails == nil ) {
cell.details = #"Loading...";
[self startInfoDownload:e forIndexPath:indexPath];
NSLog(#"Loading...");
} else {
cell.details = infodetails;
NSLog(#"Show info detail: %#", infodetails );
}
return cell;
}
- (void)infoDidFinishLoading:(NSIndexPath *)indexPath
{
infoDownloader *infoserv = [imageDownloadsInProgress objectForKey:indexPath];
if (infoserv != nil)
{
[infoservices replaceObjectAtIndex:[indexPath row] withObject:infoserv.appRecord];
NSIndexPath *a = [NSIndexPath indexPathForRow:indexPath.row inSection:0]; // I wanted to update this cell specifically
ApplicationCell *cell = (ApplicationCell *)[self.tableView cellForRowAtIndexPath:a];
cell.details = [[infoservices objectAtIndex:[indexPath row]] infoDetails];
NSLog(#"Updating=%#", [[infoservices objectAtIndex:[indexPath row]] infoDetails]);
}
}
For each cell i'm using NSURLConnection sendAsynchronousRequest to retrieve and parse xml data from object infoDownloader with
- (void)startDownload
for each individual cell.
After data has been successfully parsed delegate method from infoDownloader is called
- (void)infoDidFinishLoading:(NSIndexPath *)indexPath
The problem is that, while the
- (void)infoDidFinishLoading:(NSIndexPath *)indexPath
gets called after parsing each cell and i can see the
NSLog(#"Updating=%#", [[infoservices objectAtIndex:[indexPath row]] infoDetails]);
in the debugger with the correct details, the cell does not get refreshed immediately but after 6 or 7 seconds. Also cellForRowAtIndexPath does not get called from
- (void)infoDidFinishLoading:(NSIndexPath *)indexPath
for some reason because there is not debug output after the infoDidFinishLoading. Also i don't understand how the cell.details gets actually refreshed since cellForRowAtIndexPath isn't called again.
I've tried to setup this function using Apple's LazyTableImages loading example, which i have used successful, but i don't know what's going wrong.

Answer 1

You may need to call reloadRowsAtIndexPaths once the data has been loaded. What could be happening is that the cell data has been loaded but the cell drawing is not updated.
Also I believe your code can request the same data multiple times because if [e infoDetails] is nil a request is made, but the cell could be requested multiple times before the data is loaded so [self startInfoDownload:e forIndexPath:indexPath] would be called multiple times, downloading the same data. You should look into keeping track of which rows you have requested data for.
Check out this code for some ideas on how to solve this: https://github.com/kgn/Spectttator/blob/master/SpectttatorTest-iOS/RootViewController.m#L123

Answer 2

Any changes affecting UI must be performed on main thread.
Refreshing tableView, by changing cells details, realoading tabe view, realoding rows... are changes affecting UI.
In particular, you should perform your changes in the main thread using :
dispatch_async(dispatch_get_main_queue(), ^{
cell.details = [[infoservices objectAtIndex:[indexPath row]] infoDetails];
}
or prior to iOS 4 :
cell performSelectorOnMainThread:#selector(setDetails:) withObject:[[infoservices objectAtIndex:[indexPath row]] infoDetails];