.NET MAUI ListView Delegate Group Descriptor

DelegateGroup descriptor enables you to group by a custom key (for example, some complex expression combining two or more properties) instead of being limited by the value of a single property. This descriptor exposes the following properties:

• KeyExtractor—Defines the (Func<object, object) delegate which returns the property to retrieve the group key for each data item.
• SortOrder—Defines the sort order in each group to Ascending or Descending.

Let's use the same example from the previous section, and add DelegateGroupDescriptor through code instead.

Define the RadListView:

<telerik:RadListView x:Name="listView" 
                     ItemsSource="{Binding Cities}"
                     ItemTemplate="{StaticResource ListViewItemTemplate}"
                     GroupHeaderTemplate="{StaticResource ListViewGroupHeaderTemplate}"
                     GroupHeaderStyle="{StaticResource ListViewGroupHeaderStyle}">
    <telerik:RadListView.BindingContext>
        <local:GroupingViewModel/>
    </telerik:RadListView.BindingContext>
</telerik:RadListView>

Include the telerik namespace:

xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui" 

Create and apply a delegate for grouping the items (for example by their first letter) as following:

public DelegateGrouping()
{
    InitializeComponent();

    var delegateDescriptor = new ListViewDelegateGroupDescriptor
    {
        KeyExtractor = FirstLetterKeyExtractor
    };

    listView.GroupDescriptors.Add(delegateDescriptor);
}

private object FirstLetterKeyExtractor(object arg)
{
    var item = arg as City;
    return item?.Name.Substring(0, 1);
}

Add a business model:

public class City
{
    public string Continent { get; set; }
    public string Name { get; set; }
    public string Country { get; set; }
}

Add a ViewModel with a collection of Cities:

public class GroupingViewModel : NotifyPropertyChangedBase
{
    public ObservableCollection<City> Cities { get; set; }

    public GroupingViewModel()
    {
        this.Cities = new ObservableCollection<City>()
        {
            new City() { Name = "Barcelona", Country = "Spain", Continent = "Europe"},
            new City() { Name = "Madrid", Country = "Spain", Continent = "Europe" },
            new City() { Name = "Rome", Country = "Italy", Continent = "Europe" },
            new City() { Name = "Florence", Country = "Italy", Continent = "Europe" },
            new City() { Name = "London", Country = "England", Continent = "Europe" },
            new City() { Name = "Manchester", Country = "England", Continent = "Europe"},
            new City() { Name = "New York", Country = "USA", Continent = "North America" },
            new City() { Name = "Boston", Country = "USA",  Continent = "North America" }
         };
    }
}

The following image shows a ListView grouped through the DelegateGroupDescriptor.

For the ListView DelegateGroupDescriptor example, go to the SDKBrowser Demo Application and navigate to ListView -> Grouping category.

See Also

• Filtering
• Sorting
• Selection