Question

I have two viewmodels with an observablecollection in each viewmodel.
These collection have an relation to each other.
For instance let say one is a collection of ClassA that have an Id and a Name the other is a collection of ClassB that has an ClassAId and some OtherValue
Is it possible to databind these to a ListView so that for each item in CollectionA the OtherValue is fetched from CollectionB

   <ListView ItemsSource="{Binding ViewModelA.CollectionClassA}">
       <ListView.View>
          <GridView>                            
            <GridViewColumn DisplayMemberBinding="{Binding Path=ClassA.Name}"/>
            <GridViewColumn DisplayMemberBinding="{Binding Path=ClassB.OtherValue}"/>
          </GridView>
         </ListView.View>
    </ListView>

I hope I didn’t confuse you to much with my explanation of my question:)

Answer 1

You’re best option is to return a new collection that is formed at the view-model level based upon a new view-model (or model) that is special to that collection:

public class OtherViewModel
{
    //Expand these if you want to make it INPC
    public int Id { get; private set; }
    public string Name { get; private set; }
    public Foo OtherValue { get; private set; }
}

public class MainViewModel
{
    // Somewhere in MainViewModel, create the collection
    ObservableCollection<OtherViewModel> CreateCollection(ICollection<ClassA> a, ICollection<ClassB> b)
    {
        var mix = a.Join(b, a => a.Id, b => b.Id,
            (a, b) => new OtherViewModel { Id = a.Id, Name = a.Name, OtherValue = b.OtherValue });

        return new ObservableCollection<OtherViewModel>(mix);
    }

    // Expose the collection (possibly INPC if needed)
    public ObservableCollection<OtherViewModel> MixedCollection { get; private set; }
}

XAML:

<!-- Assuming the DataContext is MainViewModel -->
<ListView ItemsSource="{Binding MixedCollection}">
  <ListView.View>
    <GridView>                            
      <GridViewColumn DisplayMemberBinding="{Binding Path=Name}"/>
      <GridViewColumn DisplayMemberBinding="{Binding Path=OtherValue}"/>
    </GridView>
  </ListView.View>
</ListView>

---

Caveats:

• You can choose to use ObservableCollection<T> or not, it’s up to you if you need this collection to be observable.
• You can also expand your view-model to subscribe to the ClassA and ClassB collections so that it can update your main collection when they either of them change.

Either way, this should give you a good idea of the direction to go in, with some minor adjustments to fit into your code.