.NET MAUI CollectionView Delegate Group Descriptor
The difference between the DelegateGroupDescriptor and the PropertyGroupDescriptor is that the DelegateGroupDescriptor groups data by a custom key, while the PropertyGroupDescriptor groups by a defined key which is a property from the model.
This descriptor exposes the following properties:
-
KeyLookup—Defines theIKeyLookupinstance that is used to retrieve the group key for each data item. -
SortOrder(enum of typeTelerik.Maui.Controls.Data.SortOrder)—Specifies the sort order of the grouped items. The available options are:AscendingorDescending.
The following example demonstrates how to group the items in the CollectionView by using the DelegateGroupDescriptor.
1. Define the following business object:
public class DataModel : NotifyPropertyChangedBase
{
private string continent;
private string country;
private string city;
private int id;
public string Continent
{
get => this.continent;
set => this.UpdateValue(ref this.continent, value);
}
public string Country
{
get => this.country;
set => this.UpdateValue(ref this.country, value);
}
public string City
{
get => this.city;
set => this.UpdateValue(ref this.city, value);
}
public int Id
{
get => this.id;
set => this.UpdateValue(ref this.id, value);
}
}
2. Create a ViewModel class as shown below:
public class ViewModel : NotifyPropertyChangedBase
{
public ViewModel()
{
this.Locations = new ObservableCollection<DataModel>
{
new DataModel { Continent = "Europe", Country = "Austria", City = "Graz", Id = 1 },
new DataModel { Continent = "Europe", Country = "Austria", City = "Innsbruck", Id = 2 },
new DataModel { Continent = "Europe", Country = "Austria", City = "Ratz", Id = 3 },
new DataModel { Continent = "Europe", Country = "Austria", City = "Vienna", Id = 4 },
new DataModel { Continent = "Europe", Country = "Belgium", City = "Antwerp", Id = 5 },
new DataModel { Continent = "Europe", Country = "Belgium", City = "Charleroi", Id = 6 },
new DataModel { Continent = "Europe", Country = "Belgium", City = "Schaffen", Id = 7 },
new DataModel { Continent = "Europe", Country = "Denmark", City = "Copenhagen", Id = 8 },
new DataModel { Continent = "Europe", Country = "Denmark", City = "Odense", Id = 9 },
new DataModel { Continent = "Europe", Country = "France", City = "Nice", Id = 10 },
new DataModel { Continent = "Europe", Country = "France", City = "Paris", Id = 11 },
new DataModel { Continent = "Europe", Country = "Germany", City = "Baden-Baden", Id = 12 },
new DataModel { Continent = "Europe", Country = "Germany", City = "Berlin", Id = 13 },
new DataModel { Continent = "Europe", Country = "Germany", City = "Hamburg", Id = 14 },
new DataModel { Continent = "Europe", Country = "Germany", City = "Munich", Id = 15 },
new DataModel { Continent = "Europe", Country = "Germany", City = "Nuremberg", Id = 16 },
new DataModel { Continent = "Europe", Country = "Italy", City = "Bari", Id = 17 },
new DataModel { Continent = "Europe", Country = "Italy", City = "Rome", Id = 18 },
new DataModel { Continent = "Europe", Country = "Netherlands", City = "Amsterdam", Id = 19 },
new DataModel { Continent = "Europe", Country = "Netherlands", City = "Eindhoven", Id = 20 },
new DataModel { Continent = "Europe", Country = "Netherlands", City = "Rotterdam", Id = 21 },
new DataModel { Continent = "Europe", Country = "Portugal", City = "Lisbon", Id = 22 },
new DataModel { Continent = "Europe", Country = "Portugal", City = "Porto", Id = 23 },
new DataModel { Continent = "Europe", Country = "Spain", City = "Barcelona", Id = 24 },
new DataModel { Continent = "Europe", Country = "Spain", City = "Madrid", Id = 25 },
new DataModel { Continent = "Europe", Country = "United Kingdom", City = "London", Id = 26 },
new DataModel { Continent = "Europe", Country = "United Kingdom", City = "Manchester", Id = 27 },
new DataModel { Continent = "North America", Country = "United States", City = "New York", Id = 28 },
new DataModel { Continent = "North America", Country = "United States", City = "Los Angeles", Id = 29 },
new DataModel { Continent = "North America", Country = "United States", City = "Chicago", Id = 30 },
new DataModel { Continent = "North America", Country = "United States", City = "Boston", Id = 31 },
new DataModel { Continent = "North America", Country = "United States", City = "San Francisco", Id = 32 },
new DataModel { Continent = "North America", Country = "Canada", City = "Toronto", Id = 33 },
new DataModel { Continent = "North America", Country = "Canada", City = "Vancouver", Id = 34 },
new DataModel { Continent = "North America", Country = "Canada", City = "Ottawa", Id = 35 },
new DataModel { Continent = "South America", Country = "Brazil", City = "Rio de Janeiro", Id = 36 },
new DataModel { Continent = "South America", Country = "Brazil", City = "Sao Paulo", Id = 37 },
new DataModel { Continent = "South America", Country = "Brazil", City = "Salvador", Id = 38 },
new DataModel { Continent = "South America", Country = "Argentina", City = "Buenos Aires", Id = 39 },
new DataModel { Continent = "South America", Country = "Peru", City = "Lima", Id = 40 },
new DataModel { Continent = "South America", Country = "Peru", City = "Cusco", Id = 41 },
new DataModel { Continent = "South America", Country = "Colombia", City = "Bogota", Id = 42 },
new DataModel { Continent = "South America", Country = "Bolivia", City = "La Paz", Id = 43 },
new DataModel { Continent = "South America", Country = "Venezuela", City = "Caracas", Id = 44 },
new DataModel { Continent = "South America", Country = "Chile", City = "Santiago", Id = 45 },
new DataModel { Continent = "Asia", Country = "China", City = "Hong Kong", Id = 46 },
new DataModel { Continent = "Asia", Country = "China", City = "Shanghai", Id = 47 },
new DataModel { Continent = "Asia", Country = "China", City = "Macau", Id = 48 },
new DataModel { Continent = "Asia", Country = "India", City = "Delhi", Id = 49 },
new DataModel { Continent = "Asia", Country = "India", City = "Hyderabad", Id = 50 },
new DataModel { Continent = "Asia", Country = "Japan", City = "Tokyo", Id = 51 },
new DataModel { Continent = "Asia", Country = "Japan", City = "Osaka", Id = 52 },
new DataModel { Continent = "Asia", Country = "Japan", City = "Kyoto", Id = 53 },
new DataModel { Continent = "Asia", Country = "Vietnam", City = "Ho Chi Minh", Id = 54 },
new DataModel { Continent = "Asia", Country = "Vietnam", City = "Hanoi", Id = 55 },
new DataModel { Continent = "Asia", Country = "Thailand", City = "Bangkok", Id = 56 },
new DataModel { Continent = "Asia", Country = "Thailand", City = "Phuket", Id = 57 },
new DataModel { Continent = "Africa", Country = "Nigeria", City = "Lagos", Id = 58 },
new DataModel { Continent = "Africa", Country = "Egypt", City = "Cairo", Id = 59 },
new DataModel { Continent = "Africa", Country = "Algeria", City = "Algiers", Id = 60 },
new DataModel { Continent = "Oceania", Country = "Australia", City = "Sydney", Id = 61 },
new DataModel { Continent = "Oceania", Country = "Australia", City = "Melbourne", Id = 62 },
new DataModel { Continent = "Oceania", Country = "Australia", City = "Canberra", Id = 63 },
new DataModel { Continent = "Oceania", Country = "New Zealand", City = "Auckland", Id = 64 },
new DataModel { Continent = "Oceania", Country = "New Zealand", City = "Wellington", Id = 65 },
};
}
public ObservableCollection<DataModel> Locations { get; set; }
}
3. Add the RadCollectionView definition with DelegateGroupDescriptor:
<telerik:RadCollectionView x:Name="collectionView"
ItemsSource="{Binding Locations}"
DisplayMemberPath="City">
<telerik:RadCollectionView.BindingContext>
<local:ViewModel />
</telerik:RadCollectionView.BindingContext>
</telerik:RadCollectionView>
4. Include the telerik namespace:
xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"
5. Define the custom IKeyLookup:
class CustomIKeyLookup : Telerik.Maui.Controls.Data.IKeyLookup
{
public object GetKey(object arg)
{
var item = arg as DataModel;
return item?.Country;
}
}
5. Add the DelegateGroupDescriptor to the RadCollectionView:
this.collectionView.GroupDescriptors.Add(new DelegateGroupDescriptor
{
DisplayContent = "Country",
KeyLookup = new CustomIKeyLookup()
});
For a runnable demo with the CollectionView
DelegateGroupDescriptor, see the SDKBrowser Demo Application and go to the CollectionView > Grouping category.