Reload UICollectionView header or footer?

Question

I have some data that is fetched in another thread that updates a UICollectionView\'s header. However, I\'ve not found an efficient way of reloading a supplementary view suc

Answer 1

Here's what I did to update only the section headers that are currently loaded in memory:

• Add a weakToStrong NSMapTable. When you create a header, add the header as the weakly held key, with the indexPath object. If we reuse the header we'll update the indexPath.
• When you need to update the headers, you can now enumerate the objects/keys from the NSMapTable as needed.

    @interface YourCVController ()
        @property (nonatomic, strong) NSMapTable *sectionHeaders;
    @end

    @implementation YourCVContoller

    - (void)viewDidLoad {
        [super viewDidLoad];
        // This will weakly hold on to the KEYS and strongly hold on to the OBJECTS
        // keys == HeaderView, object == indexPath
        self.sectionHeaders = [NSMapTable weakToStrongObjectsMapTable];
    }

    // Creating a Header. Shove it into our map so we can update on the fly
    - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
    {
        PresentationSectionHeader *header = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"presentationHeader" forIndexPath:indexPath];
        // Shove data into header here
        ...
        // Use header as our weak key. If it goes away we don't care about it
        // Set indexPath as object so we can easily find our indexPath if we need it
        [self.sectionHeaders setObject:indexPath forKey:header];
        return header;
    }

    // Update Received, need to update our headers
    - (void) updateHeaders {
        NSEnumerator *enumerator = self.sectionHeaders.keyEnumerator;
        PresentationSectionHeader *header = nil;
        while ((header = enumerator.nextObject)) {
            // Update the header as needed here
            NSIndexPath *indexPath = [self.sectionHeaders objectForKey:header];
        }
    }

    @end