Dart: convert Map to List of Objects

List<Weight> weightData = List();

weights.forEach((k,v) => weightData.add(Weight(k,v))); 

Following on Richard Heap's comment above, I would:

List<Weight> weightData =
  mapData.entries.map( (entry) => Weight(entry.key, entry.value)).toList();

Don't forget to call toList, as Dart's map returns a kind of Iterable.