CollectionViewSource grouping one item to multiple groups

Question

I am trying to mimic the msn messenger contactlist treeview display. I have a Contact object which has a Groups property that returns an array msngroups that the Contact belongs, this meaning say I have something as per bellow

Class Contact
{
    string Name;
    string[] Groups {get;set;}
 }

 ObservableCollection<Contact> ContactList;

So a contact can be in mutiple groups, is that possible to use CollectionViewSource to generate the correct view to feed a wpf TreeView?

Answer 1

The grouping would work when you flatten this hierarchy i.e. "Contact having Groups" into "Repeated Contacts having each single group" ...

e.g.

If you have 4 items with groups like ...

Dog { mammal, quadruped }
Man { mammal, biped }
PrayingMantis { insect, quadruped }
Pegion { bird, biped }

Then you new flat list should be like this...

<mammal, Dog>
<mammal, Man>
<bird, Pigeon> 
<insect, PrayingMantis>
<biped, Man>
<biped, Pigeon>
<quadruped, Dog>
<quadruped, PrayingMantis>

So after applyin grouping on the Keys above it should be

mammal { Dog, Man }
bird { Pigeon }
insect { PrayingMantis }
biped { Man,  Pigeon }
quadruped { Dog, PrayingMantis }

C# Code:

//Flatten the groups into a KeyValuePair<string, Contacts> list using LINQ.
var flatGroups 
    = listGroups.SelectMany(
        ctc => ctc.Groups.Select(
             grp => new KeyValuePair<string, Contact>(grp, ctc))).ToList();          

//Apply CollectionViewSource group on the `Key`.
var collectionVwSrc = new CollectionViewSource();
collectionVwSrc.Source = flatGroups;
collectionVwSrc.GroupDescriptions.Add(new PropertyGroupDescription("Key"));

//Apply groups as itemssource to the TreeView.
MyGroupsTree.ItemsSource = collectionVwSrc.View.Groups; 

XAML

    <TreeView x:Name="MyGroupsTree">
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding Items}">
                <!--GroupItem.Name--> 
                <TextBlock Text="{Binding Path=Name}" 
                           FontWeight="Bold"/>
                <HierarchicalDataTemplate.ItemTemplate>
                    <DataTemplate>
                        <!--Contact.Name-->
                        <TextBlock Text="{Binding Value.Name}"/>
                    </DataTemplate>
                </HierarchicalDataTemplate.ItemTemplate>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>

Let me know if this helps...