Objective

The objective of this task is to migrate away from using TextKit 1 APIs in iOS implementation of Live Markdown.

Current state

Currently, we access .layoutManager property which causes RCTUITextView to switch back to TextKit 1 compatibility mode with the following warning:

UITextView 0x108021a00 is switching to TextKit 1 compatibility mode because its layoutManager was accessed.
Break on void _UITextViewEnablingCompatibilityMode(UITextView *__strong, BOOL) to debug.

Previous attempts

1. Define class MarkdownTextLayoutManagerDelegate that conforms to NSTextLayoutManagerDelegate
2. Create an instance of this class in [MarkdownTextInputDecoratorView didMoveToWindow:]
3. Store the instance using a strong pointer as a private field
4. Assign an instance of this class to _textView.textLayoutManager.delegate (this is a weak pointer!)
5. Define class MarkdownBlockquoteTextLayoutFragment that inherits from NSTextLayoutFragment
6. Implement drawAtPoint:inContext: to draw a rectangle and set a breakpoint inside
7. Implement textLayoutManager:textLayoutFragmentForLocation:inTextElement: method that returns an instance of MarkdownBlockquoteTextLayoutFragment

This worked successfully, however there was a new issue with alternating content offset on each keypress (see #144 (comment) for details).

Resources

• https://developer.apple.com/videos/play/wwdc2021/10061/ (tutorial + sample code)