Question

MVVM pattern is implemented in my Silverlight4 application.

Originally, I worked with ObservableCollection of objects in my ViewModel:

public class SquadViewModel : ViewModelBase<ISquadModel>
{
    public SquadViewModel(...) : base(...)
    {
        SquadPlayers = new ObservableCollection<SquadPlayerViewModel>();
        ...
        _model.DataReceivedEvent += _model_DataReceivedEvent;
        _model.RequestData(...);
    }

    private void _model_DataReceivedEvent(ObservableCollection<TeamPlayerData> allReadyPlayers, ...)
    {
        foreach (TeamPlayerData tpd in allReadyPlayers)
        {
            SquadPlayerViewModel sp = new SquadPlayerViewModel(...);
            SquadPlayers.Add(sp);
        }
    }
    ...
}

Here is a peacie of XAML code for grid displaying:

xmlns:DataControls="clr-namespace:System.Windows.Controls;
                    assembly=System.Windows.Controls.Data"
...
<DataControls:DataGrid ItemsSource="{Binding SquadPlayers}">
    ...</DataControls:DataGrid>

and my ViewModel is bound to DataContext property of the view.

This collection (SquadPlayers) is not changed after its creation so I would like to change its type to

List<SquadPlayerViewModel>

. When I did that, I also added

RaisePropertyChanged("SquadPlayers")

in the end of ‘_model_DataReceivedEvent’ method (to notify the grid that list data are changed.

The problem is that on initial displaying grid doesn’t show any record… Only when I click on any column header it will do ‘sorting’ and display all items from the list…

Question1: Why datagrid doesn’t contain items initially?
Q2: How to make them displayed automatically?

Thanks.

P.S. Here is a declaration of the new List object in my view-model:

        public List<SquadPlayerViewModel> SquadPlayers { get; set; }

Answer 1

You can’t use List as a binding source, because List not implement INotifyCollectionChanged it is require for WPF/Silverlight to have knowledge for whether the content of collection is change or not. WPF/Sivlerlight than can take further action.

I don’t know why you need List<> on your view model, but If for abstraction reason you can use IList<> instead. but make sure you put instance of ObservableCollection<> on it, not the List<>. No matter what Type you used in your ViewModel Binding Only care about runtime type.

so your code should like this:

//Your declaration
public IList<SquadPlayerViewModel> SquadPlayers { get; set; }
//in your implementation for WPF/Silverlight you should do
SquadPlayers = new ObservableCollection<SquadPlayerViewModel>();
//but for other reason (for non WPF binding) you can do
SquadPlayers = new List<SquadPlayerViewModel>();

I usually used this approach to abstract my “Proxied” Domain Model that returned by NHibernate.