Pass value from child model to parent model in MVVM

Question

Hi all,

 

I am coding an MVVM C# WPF software with 2 models. I am using Caliburn.Micro FYI.

 

The parent Model :

namespace Expense_Manager.Models

{

   public class Receipt: PropertyChangedBase

   {

      public Receipt()

      {

         Items = new List<Item>();

      }

      public List<Item> Items{ get; set; }

      private double _total;

      public double Total

      {

         get { return _total; }

         set

         {

            _total= value;

            NotifyOfPropertyChange(() => Total);

         }

      }

   }

}

 

The second model:

namespace Expense_Manager.Models

{

   public class Item: PropertyChangedBase

   {

      public Item()

      { }

      

      private double _amount;

      public double Amount

      {

         get { return _amount; }

         set

         {

            _amount= value;

            NotifyOfPropertyChange(() => Amount

         }

      }

   }

}

 

I have simplified the models for the purpose of posting this question.

 

So my question is: How can I have the Total amount in the parent model calculate itself either by:

• adding each value of the Item model everytime it is added to teh parent's items list 
• calculating the sum of each item value once the full list of items is entered in the items list (this would mean that if an item is added at a later date, it would not recalculate itself which I am not too happy about so 1 would prefer to do option 1 above)