CollectionView NSURL Session Speed and Reloading - ios

Question

I'm fairly new to iOS and developing weather App in when I download hourly forecast along with icon of conditions. I have been able to implement UICollection with NSURL Connection. However, I'm having issues regarding speed/performance issues regarding NSURL Session. Here are the two issues:
1) the speed of downloading and presenting the downloaded icons is very slow (and there are extremely small images). This download process can take anywhere from 5-10 seconds.
2) when I put a button to reset the collection, all data is reset, however the existing images remain until the new images are downloaded. Again this can take anywhere from 5-10 seconds.
Here is my code:
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return self.hours.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = #"ConditionsCell";
ConditionsCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
cell.conditionsTime.text = [self.hours objectAtIndex:indexPath.row];
cell.conditionsTemp.text = [NSString stringWithFormat:#"%#°", [self.hoursTemp objectAtIndex:indexPath.row]];
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:[NSURL URLWithString:[self.hoursIcons objectAtIndex:indexPath.row]] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
UIImage * serverImage = [UIImage imageWithData: data];
cell.conditionsImage.image = serverImage;
}];
[dataTask resume];
return cell;
}
And here is the IBAction for the button and to reload the CollectionView:
- (IBAction)selectDay:(UISegmentedControl *)sender {
if (sender.selectedSegmentIndex == 0)
{
self.todayOrTomorrow = #"today";
}
else if (sender.selectedSegmentIndex == 1)
{
self.todayOrTomorrow = #"tomorrow";
}
self.hours = [self hours];
self.hoursIcons = [self hoursIcons];
self.hoursTemp = [self hoursTemp];
[_collectionViewHours reloadData];
}

Answer 1

You are downloading data in background that, but not updating UI on main thread,try below pattern it willlhelp you
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = #"ConditionsCell";
ConditionsCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
cell.conditionsTime.text = [self.hours objectAtIndex:indexPath.row];
cell.conditionsTemp.text = [NSString stringWithFormat:#"%#°", [self.hoursTemp objectAtIndex:indexPath.row]];
cell.conditionsImage.image = [UIImage imageNamed:""];//reseting image
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:[NSURL URLWithString: [self.hoursIcons objectAtIndex:indexPath.row]] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
#autoreleasepool {//autorelease pool for memory release
if (!error) {
//UIImage * serverImage = [UIImage imageWithData: data];//comment this extra variable and can increase memory overhead.
dispatch_async(dispatch_get_main_queue(), ^{
cell.conditionsImage.image = [UIImage imageWithData: data];//update UI
});
}}//autorelease pool
}];
[dataTask resume];
return cell;
}
it will definetly help you for your first part.
Thanks.