Dart APIsettings_listSettingsListPageonSelectAppearance onSelectAppearance property Null safety VoidCallback onSelectAppearance final Implementation final VoidCallback onSelectAppearance; unself_settings_list settings_list SettingsListPage onSelectAppearance property SettingsListPage class Constructors SettingsListPage Properties hashCode key onSelectAppearance onSelectData onSelectFeedback onSelectLicense onSelectPrivacy onSelectTerms runtimeType trailing Methods build createElement debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==