Asynchronous call not refreshing table - objective-c

Question

I'm noticing some very weird behavior, I'm hoping to see if anyone else has come across this. I am making an asynchronous api call (code below). When the call completes an array is populated from the results of the call, and then I reload my table (which should cause cellForRowAtIndexPath to be called), which should update my table view with my array's data. However, the data in the tableview still doesn't appear until it needs to be reloaded from some other means - for instance, if I change views by clicking on a tab and then going back to the original view. It seems like there is some aspect of "refreshing the table" that I am missing, however I am calling reloadData when the asynchronous call returns.
Code:
-(void)refreshWeeksOffers
{
[array removeAllObjects];
NSMutableURLRequest *request =
[WebRequests createPostRequestWithApiCall:#"getResults" bodyData:#"params={\"locale\" : \"US\"}"];
[NSURLConnection
sendAsynchronousRequest:request
queue:[[NSOperationQueue alloc] init]
completionHandler:^(NSURLResponse *response,
NSData *data,
NSError *error)
{
if ([data length] >0 && error == nil)
{
// parse home page offers from resulting json
JsonParser *parser = [[JsonParser alloc] initWithData:data];
array = [parser parseHomepageResults];
[self.topWeekTable reloadData];
}
else if ([data length] == 0 && error == nil)
{
NSLog(#"Nothing was downloaded.");
}
else if (error != nil){
NSLog(#"Error = %#", error);
}
}];
[self.topWeekTable reloadData];
}
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [array count];
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if(!cell)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
}
Offer *currentOffer = (Offer *)[array objectAtIndex:indexPath.row];
cell.textLabel.text = [NSString stringWithFormat:#"%.1f%% Back", currentOffer.advertisedRate];
NSData *data = [NSData dataWithContentsOfURL:currentOffer.storeImage];
UIImage *img = [[UIImage alloc] initWithData:data];
cell.imageView.image = img;
return cell;
}

Answer 1

It's because you are invoking UIKit from a background thread, which is not supported.
Try this:
[ self.tableView performSelectorOnMainThread:#selector( reloadData ) withObject:nil waitUntilDone:NO ] ;
Another strategy which I prefer is like this:
-(void)startAsyncSomething
{
[ obj operationWithAsyncHandler:^{
[ [ NSThread mainThread ] performBlock:^{
... handle completion here ...
} ]
}]
}
You can add -performBlock: to NSThread with a category something like this:
#implementation NSThread (BlockPerforming)
-(void)performBlock:(void(^)())block
{
if ( !block ) { return ; }
[ self performSelector:#selector( performBlock: ) onThread:self withObject:[ block copy ] waitUntilDone:NO ] ;
}
#end