Dart APIunself_componentTextAreaonChanged onChanged property Null safety ValueChanged<String>? onChanged final Implementation final ValueChanged<String>? onChanged; unself_component unself_component TextArea onChanged property TextArea class Constructors TextArea Properties autofocus controller hashCode key onChanged onTap runtimeType Methods build createElement debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==