UICollectionView : Don't reload supplementary views - ios

Question

I am using a collection view to display datas fetched from the web service. I also have a supplementary view (header), which contains a UIImageView and a label. The UIImageView animates to show an array of images. The problem arises when I scroll the view. When the header is hidden and then scrolled up showing it, the app freezes briefly.
func collectionView(collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionReusableView {
let headerView = categoryView.dequeueReusableSupplementaryViewOfKind(UICollectionElementKindSectionHeader, withReuseIdentifier: "bannerHeader", forIndexPath: indexPath) as! HeaderBanner
print("Got into header")
print("THE NUMBER OF AD ITEMS IS: \(self.adItems.count)")
var sliderImages = [UIImage]()
var imageAddressArray = [String]()
if(self.adItems.count>0) {
print("AD ITEMS IS GREATER THAN 0")
for i in 0..<self.adItems.count {
imageAddressArray.append(URLEncoder.encodeURL(self.adItems[i].filePath!))
}
dispatch_async(dispatch_get_main_queue(), {
AdsImageDataFetch.fetchImageData(imageAddressArray) { result -> () in
sliderImages = result
self.animateImageView(headerView.bannerImage, images: sliderImages, label: headerView.bannerLabel)
}
})
}
return headerView
}
I think I have done this correctly. So, I was wondering if there is any way to not load the header when the scrolling takes place. New to iOS and Swift.

Answer 1

Since I couldn't find a solution I used a floating header view instead so that it wouldn't get refreshed every time on scroll. For other's who want to use the floating header view in Swift 2.0. Here is the code:
class StickyHeaderFlowLayout: UICollectionViewFlowLayout {
override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
// Return true so we're asked for layout attributes as the content is scrolled
return true
}
override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
// Get the layout attributes for a standard UICollectionViewFlowLayout
var elementsLayoutAttributes = super.layoutAttributesForElementsInRect(rect)
if elementsLayoutAttributes == nil {
return nil
}
// Define a struct we can use to store optional layout attributes in a dictionary
struct HeaderAttributes {
var layoutAttributes: UICollectionViewLayoutAttributes?
}
var visibleSectionHeaderLayoutAttributes = [Int : HeaderAttributes]()
// Loop through the layout attributes we have
for (index, layoutAttributes) in (elementsLayoutAttributes!).enumerate() {
let section = layoutAttributes.indexPath.section
switch layoutAttributes.representedElementCategory {
case .SupplementaryView:
// If this is a set of layout attributes for a section header, replace them with modified attributes
if layoutAttributes.representedElementKind == UICollectionElementKindSectionHeader {
let newLayoutAttributes = layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: layoutAttributes.indexPath)
elementsLayoutAttributes![index] = newLayoutAttributes!
// Store the layout attributes in the dictionary so we know they've been dealt with
visibleSectionHeaderLayoutAttributes[section] = HeaderAttributes(layoutAttributes: newLayoutAttributes)
}
case .Cell:
// Check if this is a cell for a section we've not dealt with yet
if visibleSectionHeaderLayoutAttributes[section] == nil {
// Stored a struct for this cell's section so we can can fill it out later if needed
visibleSectionHeaderLayoutAttributes[section] = HeaderAttributes(layoutAttributes: nil)
}
case .DecorationView:
break
}
}
// Loop through the sections we've found
for (section, headerAttributes) in visibleSectionHeaderLayoutAttributes {
// If the header for this section hasn't been set up, do it now
if headerAttributes.layoutAttributes == nil {
let newAttributes = layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: NSIndexPath(forItem: 0, inSection: section))
elementsLayoutAttributes!.append(newAttributes!)
}
}
return elementsLayoutAttributes
}
override func layoutAttributesForSupplementaryViewOfKind(elementKind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
// Get the layout attributes for a standard flow layout
let attributes = super.layoutAttributesForSupplementaryViewOfKind(elementKind, atIndexPath: indexPath)
// If this is a header, we should tweak it's attributes
if elementKind == UICollectionElementKindSectionHeader {
if let fullSectionFrame = frameForSection(indexPath.section) {
let minimumY = max(collectionView!.contentOffset.y + collectionView!.contentInset.top, fullSectionFrame.origin.y)
let maximumY = CGRectGetMaxY(fullSectionFrame) - headerReferenceSize.height - collectionView!.contentInset.bottom
attributes!.frame = CGRect(x: 0, y: min(minimumY, maximumY), width: collectionView!.bounds.size.width, height: headerReferenceSize.height)
attributes!.zIndex = 1
}
}
return attributes
}
// MARK: Private helper methods
private func frameForSection(section: Int) -> CGRect? {
// Sanity check
let numberOfItems = collectionView!.numberOfItemsInSection(section)
if numberOfItems == 0 {
return nil
}
// Get the index paths for the first and last cell in the section
let firstIndexPath = NSIndexPath(forRow: 0, inSection: section)
let lastIndexPath = numberOfItems == 0 ? firstIndexPath : NSIndexPath(forRow: numberOfItems - 1, inSection: section)
// Work out the top of the first cell and bottom of the last cell
let firstCellTop = layoutAttributesForItemAtIndexPath(firstIndexPath)!.frame.origin.y
let lastCellBottom = CGRectGetMaxY(layoutAttributesForItemAtIndexPath(lastIndexPath)!.frame)
// Build the frame for the section
var frame = CGRectZero
frame.size.width = collectionView!.bounds.size.width
frame.origin.y = firstCellTop
frame.size.height = lastCellBottom - firstCellTop
// Increase the frame to allow space for the header
frame.origin.y -= headerReferenceSize.height
frame.size.height += headerReferenceSize.height
// Increase the frame to allow space for an section insets
frame.origin.y -= sectionInset.top
frame.size.height += sectionInset.top
frame.size.height += sectionInset.bottom
return frame
}
}