Manipulating collections & the ViewModel pattern

Question

I'm relatively new to WPF, and I'm having trouble with what I'm fairly certain is a relatively simple problem.

I have my underlying data object, a Person:

class Person
{
    public string Surname {get; set; }
    public string Firstname {get; set; }
    public List<Address> Addresses {get; }
}

And I wish to display and edit this object in my WPF app. To this end I've created a ViewModel that I bind to in my xaml:

class PersonViewModel
{
    public string Fullname {get; }
    public ObservableCollection<AddressViewModel> Addresses {get; }
}

This is fine, except when it comes to manipulating my Address collection, where I can't work out what I should be doing:

• Should I add methods AddAddress, RemoveAddress etc... to my PersonViewModel class for manipulating my collection with instances of AddressViewModel
• Should I just add instances of AddressViewModel to my Addresses observable collection

Both of the above seem a bit messy - is there a better way of dealing with collections?

Answer 1

I would recommend adding commands in your ViewModel. For example, you would have a AddAddressCommand and a RemoveAddressCommand. you could bind these commands to the View (e.g. you could bind a button to the AddAddressCommand) that will execute a method in your ViewModel that will add to the collection.

        public ObservableCollection<AddressViewModel> Addresses { get; set; }

    public RelayCommand AddAddressCommand
    {
        get
        {
            if (_addAddressCommand == null)
            {
                _addAddressCommand = new RelayCommand(p => this.AddAddress_Execute());
            }
            return _addAddressCommand;
        }
    }

    private void AddAddress_Execute()
    {
        Addresses.Add(new AddressViewModel());
    }

(In the above example i'm using RelayCommand, this is a custom Class that implements ICommand, you can read more on this RelayCommand here

Also a side note: I wouldn't create an AddressViewModel I would Just have an AddressModel that implements INotifyPropertyChanged. There is no need to another address viewmodel unless you have display logic that is not in your model.