在Swift iOS中更改方向时更改UICollectionViewCell标签textColor

Question

I want to change the colour of a UILabel inside a UICollectionViewCell when the device orientation changes. How can I achieve this.

NotificationCenter.default.addObserver(self, selector: #selector(deviceOrientationDidChange),
                                           name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)

I wanted to observer orientation changed notification inside of the cell but i though it's not right, because there would be no way to remove the observer. The question is if I observe orientation changes in view controller, how do I get a reference to the UICollectionView cells inside the notification selector to change the cell's label textColor? This is what I was tried to use:

let indexPath = IndexPath(item: 0, section: 0)
if let cell = collectionView.cellForItem(at: indexPath) as? CommentCell {
    cell.displayNameLabel.textColor = .white
    cell.commentLabel.textColor = .white
}

but i can only access one cell view that indexPath. When I set an Int variable and set it value inside cellForRowAtIndexPath, nothing happens because it holds the value of the last item.

Answer 1

Put this in cellForRowAt

 if(orinatedLogic)
 {
         cell.displayNameLabel.textColor = .white
         cell.commentLabel.textColor = .white
  }
  else
  {
         cell.displayNameLabel.textColor = .blue
          cell.commentLabel.textColor = .blue
  }

and reload the collection whenever orientation changed

Answer 2

If you are using Storyboard you can use Vary for traits to change your label colour depending upon the orientation.

Answer 3

There is lot of possibilities depends on you requirements. I assume you don't want to reload entire collection view. But you can enumerate all visible cells and either reload them,

collectionView.reloadItems(at: collectionView.indexPathsForVisibleItems)

or change them directly.

collectionView.visibleCells.flatMap{ $0 as? CommentCell}.forEach {
    $0.commentLabel.textColor = ...
}

Answer 4

For Orientation change you can simply add

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {

    super.viewWillTransition(to: size, with: coordinator)

       collectionView.reloadItems(at: collectionView.indexPathsForVisibleItems)

}

In your collection view cell for item

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "item", for: indexPath) as! YourCellType

    cell.displayNameLabel.textColor = UIDevice.current.orientation.isPortrait ? .white : .red

    cell.commentLabel.textColor = UIDevice.current.orientation.isPortrait ? .white : .red

}

That's It , You did it !!