Action Subclassing

Suppose we have the following app state:

class AppState {  
  List<Item> items;    
  Item? selectedItem;
  // ...
}

class Item {
  String id;
  // ...
}

And then we have an action, which selects an item by id:

class SelectItem extends AppAction {
  final int id;
  SelectItem(this.id);
    
  AppState reduce() {
    Item? item = state.items.firstWhereOrNull((item) => item.id == id);
    if (item == null) throw UserException('Item not found');
    return state.copy(selectedItem: item);
  }    
}

You would use it like this:

var item = Item('A'); 
dispatch(SelectItem(item));

Since all actions extend ReduxAction<AppState>, you may use object-oriented principles to reduce boilerplate. Start by creating an abstract base action class to allow easier access to the sub-states of your store.

You could name is BaseAction, Action or any other name. Here, we'll call it AppAction:

abstract class AppAction extends ReduxAction<AppState> {

  // Getter shortcuts   
  List<Item> get items => state.items;
  Item get selectedItem => state.selectedItem;
  
  // Selectors 
  Item? findById(int id) => items.firstWhereOrNull((item) => item.id == id);
  Item? searchByText(String text) => items.firstWhereOrNull((item) => item.text.contains(text));
  int get selectedIndex => items.indexOf(selectedItem);  
}

And then your actions have an easier time accessing the store state:

class SelectItem extends AppAction {
  final int id;
  SelectItem(this.id);
    
  AppState reduce() {
    Item? item = findById(id); // Here!
    if (item == null) throw UserException('Item not found');
    return state.copy(selected: item);
  }    
}

The difference above is that, instead of writing:

Item? item = state.items.firstWhereOrNull((item) => item.id == id); 

You can simply write:

Item? item = findById(id);

It may seem a small reduction of boilerplate, but it adds up.

In practice, your base action class may end up containing a lot of elaborate "selector methods", which then can be used by all your actions.

The only requirement is that your actions now extend AppAction instead of ReduxAction<AppState>.