Anonymous Objects with Strongly Type Properties in Dart and Flutter

I am using the following code in my Dart which uses redux and flutter_redux packages. Everything works fine but as you can see I have to use the following syntax to call the appropriate action.

callback['onIncrement'](34) 

It works but it is ugly. How can I improve it so it reads more like this:

callback.onIncrement(34)

Here is the code:

StoreConnector<AppState,Map<String,Function>>(
    converter: (store) {
      return {
        'onIncrement': (value) => store.dispatch(IncrementAction(value)), 
        'onDecrement': () => store.dispatch(Actions.decrement)
      };
    },
    builder: (context, callback) {
      return Column(
        children: <Widget>[
          FlatButton(
          child: Text('Increment Counter', style: TextStyle(color: Colors.white)),
          color: Colors.orange, 
          onPressed: () => callback['onIncrement'](1)

UPDATE:

Now, I am using enums and it is little better:

StoreConnector<AppState,Map<Actions,Function>>(
        converter: (store) {
          return {
            Actions.increment: (value) => store.dispatch(IncrementAction(value)), 
            Actions.decrement: () => store.dispatch(Actions.decrement)
          };
        },
        builder: (context, callback) {
          return Column(
            children: <Widget>[
              FlatButton(
              child: Text('Increment Counter', style: TextStyle(color: Colors.white)),
              color: Colors.orange, 
              onPressed: () => callback[Actions.increment](23)

Solution 1: Hugo Passos

As far as I'm concerned, it's not possible to do this in Dart. You should work with ViewModel instead:

StoreConnector<AppState, ViewModel>(
  converter: ViewModel.fromStore,
  builder: (context, viewModel) {
    return FlatButton( 
      onPressed: () => viewModel.onIncrement(1),
      ...
    );
  },
}

...

class ViewModel {
  final void Function(int) onIncrement;
  final void Function(int) onDecrement;

  ViewModel({@required this.onIncrement, @required this.onDecrement});

  factory ViewModel.fromStore(Store store) {
    return ViewModel(
      onIncrement: (value) => store.dispatch(IncrementAction(value)),
      onDecrement: (value) => store.dispatch(DecrementAction(value)),
    );
  }
}