AppKit: NSFormatter maxLength with Korean IME composition not applied consistently

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Created 5d

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Environment

Description I set a formatter to allow only 1 character.
When typing with Korean IME, the field sometimes shows 2 characters while typing.

Question How should I handle this case? Should it be done in NSFormatter or in the field editor (NSTextView)?

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Answer 1

5d

**i've tried **

Formatter-only (isPartialStringValid…) — still see composition phases where length appears > 1 and rejection leads to awkward UX / broken composition.
Delegate + hasMarkedText (via field editor NSTextView) — clamp only when hasMarkedText == NO. Works better, but timing can still allow transient over-length during composition.
Notification approach (NSControlTextDidChangeNotification) — similar limitations to (2); timing depends on field editor behavior.

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