Maintaining the collection in a List/ObservableCollection

Question

i have been successfully adding an item to list in a MVVM, and now my problem is maintaining the list in the view model. Every time i navigate to a page or go back to a page and return to that listview, the list resets. how will i able to achieve that? i am currently using the prism to build the MVVM.

The ViewModel:

public ObservableCollection<CartData> _cartData;

public ObservableCollection<CartData> CartData
        {

         get {
               if (_cartData == null)
                {
                    _cartData = new ObservableCollection<CartData>();
                }
             return _cartData;
             }
        set {

                SetProperty(ref _cartData, value);
           }
        }




        private DelegateCommand _addItemCommand;
        public ICommand AddItemCommand
        {
            get
            {
                if (_addItemCommand == null)
                {
                    _addItemCommand = new DelegateCommand(AddToCart);
                }
                return _addItemCommand;
            }
        }

        public void AddToCart() {

CartData.Add(new CartData { Cakename = "Black Forest", Cakeprice = 104 });
                   }

Answer 1

You should be persisting the list to a permanent location, then calling it back up.  This is the same whether or not you use MVVM.

---

Matt Small - Microsoft Escalation Engineer - Forum Moderator
If my reply answers your question, please mark this post as answered.

NOTE: If I ask for code, please provide something that I can drop directly into a project and run (including XAML), or an actual application project. I'm trying to help a lot of people, so I don't have time to figure out weird snippets with undefined objects and unknown namespaces.

Answer 2

Two alternatives if you chose not to have an overhead of reading from disk frequently 1) to use a static reference to the data and access this in the VM constructor, or 2) use the IOC pattern by using a dependency injection container and have the data injected into the constructor of the view model. There pros and cons to all three depending on the app.