Flutter Developer Documents Three Refactoring Attempts on an 800-Line State Class

A Flutter developer shared a detailed account of trying to refactor an 800-line HomeScreen State class that had grown unmanageable by mixing too many unrelated responsibilities. The first approach used Dart mixins extracted into separate files, but failed because Dart's underscore prefix denotes library-level privacy, not class-level privacy, making private members inaccessible across file boundaries. A second attempt used Dart's 'part' directive to share private members across files, but top-level functions in part files lack a 'this' context, breaking access to instance methods and properties. Each failed attempt revealed a distinct constraint in Dart's language design around visibility and file boundaries. The write-up serves as a practical reference for Flutter developers facing similar large-State refactoring challenges, ultimately pointing toward a solution that accounts for these Dart-specific limitations.