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Observable Groups

Provides helper class to easily create grouped collections that can be used in ListView or GridView controls to display grouped items.

ObservableGroup<TKey, TValue>

A group of TValue objects with a key of type TKey.

It is an implementation of IGrouping<Tkey, TValue> based on ObservableCollection<TValue>. It is used by ObservableGroupedCollection<TKey, TValue> to represent the groups.

Property Type Description
Key TKey The key of the group.

ObservableGroupedCollection<TKey, TValue>

A list of groups that can be used by a CollectionViewSource to display groups in a ListView or GridView. Each group inside the collection has an observable TKey key and contains TValue values.

It is an ObservableCollection<ObservableGroup<TKey, TValue>> so groups can be added to the collection using the regular methods of ObservableCollection<T>.

// Grab a sample type
public class Person
{
    public string Name { get; set; }
}

// Set up the original list with a few sample items
var contacts = new[]
{
    new Person { Name = "Staff" },
    new Person { Name = "Swan" },
    new Person { Name = "Orchid" },
    new Person { Name = "Flame" },
    new Person { Name = "Arrow" },
    new Person { Name = "Tempest" },
    new Person { Name = "Pearl" },
    new Person { Name = "Hydra" },
    new Person { Name = "Lamp Post" },
    new Person { Name = "Looking Glass" },
};

// Group the contacts by first letter
var grouped = contacts.GroupBy(GetGroupName).OrderBy(g => g.Key);

// Create an observable grouped collection
var contactsSource = new ObservableGroupedCollection<string, Person>(grouped);

// Set up the CollectionViewSource
var cvs = new CollectionViewSource
{
    IsSourceGrouped = True,
    Source = contactsSource,
};

// Bind the CollectionViewSource to anything that supports grouped collections.
ContactsList.ItemsSource = cvs.View;

ReadOnlyObservableGroup<TKey, TValue>

Represents a read-only ObservableGroup<TKey, TValue>. This class is a read-only wrapper around an ObservableGroup<TKey, TValue>. If changes are made to the underlying collection, the ReadOnlyObservableGroup<TKey, TValue> reflects those changes.

ReadOnlyObservableGroupedCollection<TKey, TValue>

Represents a read-only ObservableGroupedCollection<TKey, TValue>. This class is a read-only wrapper around an ObservableGroupedCollection<TKey, TValue>. If changes are made to the underlying collection, the ReadOnlyObservableGroupedCollection<TKey, TValue> reflects those changes.

IReadOnlyObservableGroup

This interface allows us to use x:Bind with ObservableGroup{TKey, TValue} and ReadOnlyObservableGroup{TKey, TValue} by providing a non-generic type that we can declare using x:DataType. It extends INotifyPropertyChanged.

<DataTemplate x:Key="GroupDataTemplate"
              x:DataType="collections:IReadOnlyObservableGroup">
    <StackPanel Orientation="Horizontal">
        <TextBlock Style="{StaticResource SubtitleTextBlockStyle}"
                   Text="{x:Bind (x:String)Key}" />
        <TextBlock Margin="8,0,0,0"
                   VerticalAlignment="Bottom"
                   Opacity="0.8"
                   Style="{StaticResource CaptionTextBlockStyle}"
                   Text="{x:Bind system:String.Format('{0} item(s)', Count), Mode=OneWay}" />
    </StackPanel>
</DataTemplate>
Property Type Description
Key object The key of the group. It is immutable.
Count int The number of items currently in the grouped collection.

Sample Project

Observable group Sample Page.

You can see this in action in the Windows Community Toolkit Sample App.

Requirements

Implementation .NET Standard 2.0.
Namespace Microsoft.Toolkit
NuGet package Microsoft.Toolkit

API