Flutter Calculating the total price of the items in thier category

Issue

To-Do App

class ToDoItem{
  final String id;
  final String title;
  final Color color;
  final int price;
  final IconData icon;
  final String todoListId;

  const ToDoItem({
    @required this.color,
    @required this.id,
    @required this.todoListId,
    @required this.price,
    @required this.title,
    @required this.icon,
  });}

I am struggling to add up the total sum of items price in the to-Do lists that is equal to todoListId for example :

THE LISTS SCREEN

THE LISTS ITEMS SCREEN

so I am trying to calculate the Total Items Price

this is what I have tried:

  List<Map<String, Object>> get totalItemsPrice{
    return List.generate(1, (index) {
      var totalPriceSum = 0.0;
      for (var i = 0; i < toDo.length; i++) {
        totalPriceSum = toDo[index].amount + totalPriceSum ;
      }
      return {
        'price': totalSum,
      };
    }).toList();
  }

  double get totalPriceSum {
    return totalItemsPrice.fold(0.0, (sum, item) {
      return sum + item['price'];
    });
  }

the toDo looks like this:

List<ToDO> toDo= [];

But it is not working it is calculating the total price of all of the to-do items when I want it to only calculate the total price of the items that are in their category

Solution

If you want to filter based on the item's todoListId then you will need to provide it to the method. From there, use a where before the fold to only sum items with the matching id:

double totalPriceSum(int todoListId) {
  return ItemsPrice.where((item) => item.todoListId == todoListId)
                   .fold(0.0, (sum, item) => sum + item['price']); 
}

Answered By - Abion47