This works because attribute fixing seems to be part of the call chain before the NSLayoutManager is notified. To simplify the explanation, let’s assume you subclass NSTextStorage and override processEditing() to apply syntax highlighting as advertised on objc.io:Ĭlass CustomTextStorage : NSTextStorage Others use the NSTextStorageDelegate.textStorage(_:willProcessEditing:range:changeInLength:) callback with similar results. Illustrated in steps, it looks like this when you edit a line at the beginning and change the color of the whole line in accordance to the syntax: The user types #, followed by a space character, to change the text line to a heading in Markdown and ends up with the caret at the end of the lineĪ lot of examples on the web are based off of NSTextStorage subclasses.

Instead, subscribe to NSText.didChangeNotification, or hook into NSTextViewDelegate.textDidChange(_:) (actually declared in its ancestor protocol, NSTextDelegate.textDidChange(_:)) Description of the Problem TL DR: Do not perform style changes inside of NSTextStorage.processEditing() or NSTextStorageDelegate methods.

In short: when you type and the attributes of the line change, the insertion point is moved to the end of the line. On iOS, this does maybe not happen at all, but when you want to write syntax highlighting code for macOS apps, copying together stuff from around the web, you’ll end up with broken application behavior.

Why the Selection Changes When You Do Syntax Highlighting in a NSTextView and What You Can Do About It

Markdown monster keeps crashing