CODEWITHSUNDEEP
iosuicollectionviewuicollectionviewlayout
Payal Maniyar
Payal Maniyar

Reputation: 4402

Resize the cell of UICollectionView without the reload methods

How can I resize the cell size of UICollectionView without reload methods? Just want to call following method on some event. I do not want to reload UICollectionView or any of its section or row.

   func collectionView(collectionView: UICollectionView,
                    layout collectionViewLayout: UICollectionViewLayout,
                           sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize

Upvotes: 13

Views: 12074

Answers (3)

Zafar Ahmad
Zafar Ahmad

Reputation: 3219

I'm showing the video inside UICollectionViewCell. I've seen that UIView.animate doesn't work correctly for updating the height with fade animation. The below code works perfectly.

collectionView.performBatchUpdates({
    collectionView.collectionViewLayout.invalidateLayout()
})

Upvotes: 1

Payal Maniyar
Payal Maniyar

Reputation: 4402

I got the solution to my question with following line of code.

collectionView?.collectionViewLayout.invalidateLayout()

N.B. To animate this resizing, use UIView.animate :

let duration: TimeInterval = 0.3
UIView.animate(withDuration: duration, animations: {
    collectionView.collectionViewLayout.invalidateLayout() 
})

Upvotes: 56

deniz
deniz

Reputation: 975

I can confirm that Payal Maniyar's solution also works for UICollectionCompositional layouts as well. In my situation, I had a CollectionViewCell which only embedded a UITextView. Compositional layout correctly figured out the initial size of the text view in the cell. (Side note: you do this by disabling scrolling within the UITextView since it is already inside of another scrollable view). The problem was as the user typed directly into the text view, I wanted to change the height of the cell without reloading it. I wanted to avoid reloading the cell for 2 reasons. a) the reloaded cell flickers as the user types, b) the text view loses focus; thereby, forcing the user to click on the text view again to continue to type. So my solution is as follows:

  1. I have a cell with only UITextView inside of it where the cell is also the UITextView's delegate as such:

    class MyCollectionCell: UICollectionViewCell {
  @IBOutlet private weak var myTextView: UITextView!
  //this local variable used to determine if the intrinsic content size has changed or not
  private var textViewHeight: CGFloat = .zero
  ...
  ...
  override func awakeFromNib() {
   super.awakeFromNib()
   myTextView.delegate = self
  }
  ...
  ...
}

  2. Conform this cell to UITextViewDelegate

    extension MyCollectionCell: UITextViewDelegate { 

func textViewShouldBeginEditing(_ textView: UITextView) -> Bool {
  //this assumes that collection view already correctly laid out the cell
  //to the correct height for the contents of the UITextView
  //textViewHeight simply needs to catch up to it before user starts typing
  let fittingSize = textView.sizeThatFits(CGSize(width: myTextView.frame.width, height: CGFloat.greatestFiniteMagnitude))
  textViewHeight = fittingSize.height

  return true
}

func textViewDidChange(_ textView: UITextView) {
  //flag to determine whether textview's size is changing
  var shouldResize = false
  //calculate fitting size after the content has changed
  let fittingSize = textView.sizeThatFits(CGSize(width: myTextView.frame.width, height: CGFloat.greatestFiniteMagnitude))

  //if the current height is not equal to 
  if textViewHeight != fittingSize.height {
    shouldResize = true
    //save the new height 
    textViewHeight = fittingSize.height
  }

  //notify the cell's delegate (most likely a UIViewController) 
  //that UITextView's intrinsic content size has changed
  //perhaps with a protocol such as this:
  delegate?.textViewDidChange(newText: textView.text, alsoRequiresResize: shouldResize)
}

  3. Then when the delegate receives the notification, perhaps saves the updated text and updates the layout such as this:

    myCollectionView.collectionViewLayout.invalidateLayout()

The best part of this solution is that you do not have to invoke collectionView(_:layout:sizeForItemAt:) to resize the cell because you are not using the clunky FlowLayout to begin with.

Cheers!

Upvotes: 1

Related Questions