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CUSTOM_CELLS.md

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MessageKit Custom Cell Guide(s)

How can I add a custom cell?

Note: If you choose to use the .custom kind you are responsible for all of the cell's layout. You can design the cell in code or Interface Builder. Any UICollectionViewCell can be returned for custom cells which means any of the styling you provide from the MessageDisplayDelegate will not affect your custom cell, even if you subclass your cell from MessageContentCell.

Creating a custom cell involves four parts:

  1. Build a cell in Interface Builder or code that inherits from UICollectionViewCell
  2. Set the size of your cell. Subclass MessageSizeCalculator if you want your cell to have the default MessageKit layout design. Subclass CellSizeCalculator if you want to further customize your own cell design. The implementation of this class will allow your custom cell to automatically size itself within the messagesCollectionView.
  3. Add your custom cell size to the collection view flow layout. Subclass MessagesCollectionViewFlowLayout, and use the custom message size calculator from step 2, above.
  4. Register your custom cell and reference your custom collection view flow layout.

Example:

Let's take a look at what it takes to create a custom cell that displays a red block for your custom message.

  • 1. Custom Cell: We create a cell that inherits from UICollectionViewCell MyCustomCell.swift
open class MyCustomCell: UICollectionViewCell {
    open func configure(with message: MessageType, at indexPath: IndexPath, and messagesCollectionView: MessagesCollectionView) {
        self.contentView.backgroundColor = UIColor.red
    }
}
  • 2. MessageSizeCalculator: We set the size of our cell by creating a class that inherits from MessageSizeCalculator CustomMessageSizeCalculator.swift
open class CustomMessageSizeCalculator: MessageSizeCalculator {
    open override func messageContainerSize(for message: MessageType) -> CGSize {
    // Customize this function implementation to size your content appropriately. This example simply returns a constant size
    // Refer to the default MessageKit cell implementations, and the Example App to see how to size a custom cell dynamically
        return CGSize(width: 300, height: 130)
    }
}
  • 3. MessageFlowLayout: We add our custom message size calculator to our collection view layout by creating a class that inherits from MessagesCollectionViewFlowLayout MyCustomMessagesFlowLayout.swift
open class MyCustomMessagesFlowLayout: MessagesCollectionViewFlowLayout {
    lazy open var customMessageSizeCalculator = CustomMessageSizeCalculator(layout: self)

    override open func cellSizeCalculatorForItem(at indexPath: IndexPath) -> CellSizeCalculator {
        //before checking the messages check if section is reserved for typing otherwise it will cause IndexOutOfBounds error
        if isSectionReservedForTypingIndicator(indexPath.section) {
            return typingIndicatorSizeCalculator
        }
        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)
        if case .custom = message.kind {
            return customMessageSizeCalculator
        }
        return super.cellSizeCalculatorForItem(at: indexPath);
    }
}
  • 4. Implementation: We register our custom cell and reference our newly created MyCustomMessagesFlowLayout.swift ConversationViewController.swift
internal class ConversationViewController: MessagesViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        messagesCollectionView = MessagesCollectionView(frame: .zero, collectionViewLayout: MyCustomMessagesFlowLayout())
        messagesCollectionView.register(MyCustomCell.self)
        //...
    }
//...
    override open func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        guard let messagesDataSource = messagesCollectionView.messagesDataSource else {
            fatalError("Ouch. nil data source for messages")
        }
        //before checking the messages check if section is reserved for typing otherwise it will cause IndexOutOfBounds error
        if isSectionReservedForTypingIndicator(indexPath.section){
            return super.collectionView(collectionView, cellForItemAt: indexPath)
        }
        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)
        if case .custom = message.kind {
            let cell = messagesCollectionView.dequeueReusableCell(MyCustomCell.self, for: indexPath)
            cell.configure(with: message, at: indexPath, and: messagesCollectionView)
            return cell
        }
        return super.collectionView(collectionView, cellForItemAt: indexPath)
    }
}