GroupedObservableCollection

An implementation of ObservableCollection that allows for grouped data to be presented in a XAML type of UI, providing support for updates to the underlying data.

Quick start

The demo UWP app in the repo shows most of these principals.

Create a new collection from an existing set of data:

var carList = GetListOfCarsFromSomewhere();

// Imaginary type called Car with a string property "Model"
// The delegate instructs the collection what data should be used to group entries together
var groupedCollection = new GroupedObservableCollection<string, Car>(c => c.Model, carList);

Bind that to a CollectionViewSource (or alternatively set it programmatically in code behind):

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.Resources>
        <CollectionViewSource IsSourceGrouped="True" x:Name="Source" Source="{Binding GroupedCollection}" />
    </Grid.Resources>
    ...

Configure a ListView to work from the CollectionViewSource:

<ListView ItemsSource="{Binding Source={StaticResource Source}}">
    <ListView.GroupStyle>
        <GroupStyle>
            <GroupStyle.HeaderTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Key}" />
                </DataTemplate>
            </GroupStyle.HeaderTemplate>
        </GroupStyle>
    </ListView.GroupStyle>
    <ListView.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Name}" />
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

And then you can manipulate the collection as much as you like behind the scenes - the UI will stay in sync.

Simple collection operations

// Add an item - the correct group will automatically be appended to
myCollection.Add(new Car { ... });

// Remove an item from - the correct group with be removed from. If the item is the last in the group,
// the group itself will be removed
myCollection.Remove(car);

// Test for the existence of an item
myCollection.Contains(car);

// Enumerate all the items in the collection in group order
var allCars = myCollection.EnumerateItems().ToList();

// Enumerate all the group keys in the collection
var allKeys = myCollection.Keys.ToList();

Advanced collection operations

ReplaceWith(GroupedObservableCollection<TKey, TElement> replacement, IEqualityComparer comparer)

This method supports the scenario where an initial set of data needs to be refreshed with an updated list:

Items that exist in the current collection and in the replacement will remain
Items that are in the current collection, but are no longer in the replacement will be removed
New items unique to the replacement collection will be added
The order of items will be updated in the current collection to be consistent with the replacement collection

ReplaceWith feels like a bad name. I considered MergeWith, but it's not really a merge because items are deleted from the collection as well as added, i.e. the replacement always wins. Alternative suggestions welcome :)

Current limitations