Dart/Flutter: StatefulWidget + TextEditingController + FutureBuilder

future.dart

class EditCaptionView extends StatefulWidget {
  final String postId;
  const EditCaptionView({super.key, required this.postId});

  @override
  State<EditCaptionView> createState() => _EditCaptionViewState();
}

class _EditCaptionViewState extends State<EditCaptionView> {
  final _controller = TextEditingController();
  late final Future<PostModel?> _post;

  @override
  void initState() {
    super.initState();
    _post = () async {
      final post = await PostRepository().get(widget.postId);
      // TODO: what if _controller is already disposed?
      // I put this line here, not in build() or builder(), to avoid to get it called multiple times.
      _controller.text = post?.caption.text ?? '';
      return post;
    }();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<PostModel?>(
      future: _post,
      builder: (BuildContext context, AsyncSnapshot<PostModel?> snapshot) {
        ...
      }
     );
  }
}

Check out https://stackoverflow.com/a/50337157