Why is CompositeCollection not Freezable?

Question

I am writing an application using the MVVM pattern. I am providing data to my view by setting my view\'s DataContext property to an instance of my ViewModel. Generally I j

Answer 1

I just tried this tonight:

public class State
{
    public string Code { get; set; }
    public string Name { get; set; }
}

public class MyWindowViewModel
{
    ObservableCollection<State> _states = new ObservableCollection<State>
    {
        new State { Code = "FL", Name = "Florida" },
        new State { Code = "CA", Name = "California" },
    };

    public ObservableCollection<State> States
    {
        get
        {
            return _states;
        }
    }
}

<Window x:Class="WpfApplication1.MyWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:app="clr-namespace:WpfApplication1"
        Title="Window1"
        Height="300"
        Width="300">

  <Window.Resources>
    <app:ServiceLocator x:Key="Locator" />
  </Window.Resources>

  <StackPanel>
    <ComboBox x:Name="TestCombo" SelectedIndex="0" DisplayMemberPath="Name" SelectedValuePath="Code">
      <ComboBox.ItemsSource>
        <CompositeCollection>
          <app:State Code="" Name="Select a state..." />
          <app:State Code="TX" Name="Texas" />
          <CollectionContainer Collection="{Binding Source={StaticResource Locator}, Path=MyWindowViewModel.States}" />
        </CompositeCollection>
      </ComboBox.ItemsSource>
    </ComboBox>
  </StackPanel>
</Window>

The key here is to create an instance of your service locator as a static resource then go through it to get to your viewmodel. The service locator can wire up to instances of the ViewModel using Unity or whatever DI you want.

Edit:

Actually in my silverlight app I create the service locator as a static resoure in the App.xaml and then bind my other UserControls/Windows/Pages DataContext to a ViewModel property of the service locator. It should still work the same way for the combo boxes though even if the service locator is instantiated in the App.xaml's resources. I wish there was a silverlight version of CompositeCollection that I could use. This would work great for the app I'm working on. :(