滚动后，collectionView中可重用单元的子视图大小错误

Question

I have a collectionView for a chat page. I created an UICollectionViewCell subclass named TextChatCollectionViewCell . I have another class that fills my collection view and specify a CGSize for each item (following UICollectionViewDelegateFlowLayout and UICollectionViewDataSource protocols).

The cell frame size is correct but subviews have a wrong frame size when I scroll, probably because dequeueReusableCell return an instance of another cell and subviews doesn't reload, I tried to call layoutIfNeeded() to force the layout of subviews drawing again but it has no effect.

My xib file for my cell with constraints :

My code to fill and return cell :

public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    guard let cell = self.manager.collectionView.dequeueReusableCell(withReuseIdentifier: "TextChatCollectionViewCell", for: indexPath) as? TextChatCollectionViewCell else {
        return UICollectionViewCell()
    }

    self.fillCellUsingMessageUUID(cell, self.messagesUUIDs[indexPath.row]) // Hide labelDate (set height to 0 for the moment), fill UITextView etc...


    print("=================\(self.messagesUUIDs[indexPath.row])===================")
    print("Cell text : " + cell.textMessage.text)
    print("Cell frame size : " + cell.frame.size.debugDescription)
    print("UITextView frame size : " + cell.textMessage.frame.size.debugDescription)
    print("UITextView parent size : " + cell.textBackgroundView.frame.size.debugDescription)
    print("Cell content view frame size : " + cell.globalView.frame.size.debugDescription)
    print("====================================")
    return cell
}

My debug output :

=================B00C74D6-C3F1-4039-948B-0BAC59DC0D83===================

Cell text : "Ggg"
Cell frame size : (320.0, 80.0) // Expected size
UITextView frame size : (240.0, 59.5) // Wrong height
UITextView parent size : (240.0, 59.5) // Wrong height
Cell content view frame size : (320.0, 59.5) // Wrong height
====================================
=================2704FFF5-17D1-4E0E-9399-DD7EB4C60D36===================
Cell text : "Zyehdhzhdhdhzhejajeksvshdjajdjhhhjhhjjhhhhthhytgjuhjjyghjuyghhuygghuutghjutghkiygvcwqazdxcfeerggvbhtyjjnkkuilloomppolpôkkjjîîîukhgkurghhhhhgoohgosohsohdohsohsohshowlhdlhslhslhsglslydlgsotwyod [...]"
Cell frame size : (320.0, 411.5) // Expected size
UITextView frame size : (240.0, 59.5) // Wrong height
UITextView parent size : (240.0, 59.5) // Wrong height
Cell content view frame size : (320.0, 59.5) // Wrong height

Expected output :

=================B00C74D6-C3F1-4039-948B-0BAC59DC0D83===================

Cell text : "Ggg"
Cell frame size : (320.0, 80.0)
UITextView frame size : (240.0, 80.0)
UITextView parent size : (240.0, 80.0)
Cell content view frame size : (320.0, 80.0)
====================================
=================2704FFF5-17D1-4E0E-9399-DD7EB4C60D36===================
Cell text : "Zyehdhzhdhdhzhejajeksvshdjajdjhhhjhhjjhhhhthhytgjuhjjyghjuyghhuygghuutghjutghkiygvcwqazdxcfeerggvbhtyjjnkkuilloomppolpôkkjjîîîukhgkurghhhhhgoohgosohsohdohsohsohshowlhdlhslhslhsglslydlgsotwyod [...]"
Cell frame size : (320.0, 411.5) 
UITextView frame size : (240.0, 411.5) 
UITextView parent size : (240.0, 411.5)
Cell content view frame size : (320.0, 411.5)

Answer 1

It's probably the constraint's are not getting updated before you assign new values to the cell.

Here is a small code which I hope should fix it. layoutIfNeeded()

Just call this on the Cell before you assign new values to it, like

cell.layoutIfNeeded()

Did fix a lot of issues for me. Hope it helps you.