How to retain previous selection in collectionview after reload in Apple TV - uitableview

Question

Hi in my Apple TV application i have one left collectionview right collectionview.Like splitview.When ever i focus cell on left data will refresh on right and when i select any cell in right collection view i am refreshing left and right collectionviews with new data (Like next level).And when on click on menu i will refresh both collectionviews with old data (Like coming to previous level). I want to highlight cell in left collectionview with red colour but i am reloading left collectionview while going forward or coming backward so always first cell is highlighting with Red colour. Can anyone suggest how to maintain previous selection in left collection-views because i am using only one collectionview for left menu and just reloading data.

Answer 1

The easiest way to retain focus in a UITableView or UICollectionView is to use UICollectionView.remembersLastFocusedIndexPath = true. This will automatically restore focus to the last focused item in a collection/table view and also automatically focus on the first item if there was no previously focused item or if the collection view data is reloaded.
If you need more control, the next level is to set UICollectionView.remembersLastFocusedIndexPath = false and use UICollectionViewDelegate.indexPathForPreferredFocusedView from your UIViewController instead. This method is only called whenever focus changes to a collection view programmatically though (but not if focus changes to a collection view as a result of TV remote interaction).
Now to ensure that indexPathForPreferredFocusedView is called when you switch between the left and right collection views using a TV remote, you will need to intercept shouldUpdateFocusInContext to override focus switches between the left and right collection view programmatically:
override func shouldUpdateFocusInContext( ... ) -> Bool {
if let nextView: UIView = context.nextFocusedView, let previousView: UIView = context.previouslyFocusedView{
if (nextView.isDescendant(of:leftCollectionView) && previousView.isDescendant(of:rightCollectionView)){
setFocusTo(leftCollectionView) // will invoke delegate indexPath method
return false // prevent system default focus change in favor of programmatic change
}
else if (nextView.isDescendant(of:rightCollectionView && previousView.isDescendant(of:leftCollectionView){
setFocusTo(rightCollectionView) // will invoke delegate indexPath method
return false
}
}
return true
}
internal var focusedView: UIView?
internal func setFocusTo(_ view:UIView){
focusedView = view
setNeedsFocusUpdate()
}
override var preferredFocusEnvironments -> [UIFocusEnvironment]{
return focusedView != nil ? [focusedView!] : super.preferredFocusEnvironments
}
func indexPathForPreferredFocusedView(in collectionView: UICollectionView) -> IndexPath? {
...
}
Alternatively, instead of using setFocusTo( collectionView ) + indexPathForPreferredFocusedView, you can just use setFocusTo( collectionViewCell ). Overriding indexPathForPreferredFocusedView is more robust though since it catches all cases where focus shifts for reasons other than user interaction (ex: system focus update due to an alert displaying + dismissing)