How can I decode a hexadecimal to a byte array in Dart?
HexDecoder isn't actually in dart:convert. It's in a package (also) called convert.
You need to add it to your pubspec.yaml and then use an import like:
import 'package:convert/convert.dart';Then use it like this:
hex.decode('abcdef');hex is a const singleton instance of the codec. (The constructor is private; you don't need to instantiate your own - use the existing const instance.)