<syncfusion:SfListView.DataSource>
                    <data:DataSource>
                        <data:DataSource.GroupDescriptors>
                            <data:GroupDescriptor KeySelector="tramoProperty" PropertyName="tramo" />
                            <data:GroupDescriptor KeySelector="fechaProperty" PropertyName="fechasalidatramo" />
                        </data:DataSource.GroupDescriptors>
                    </data:DataSource>
                </syncfusion:SfListView.DataSource>

<syncfusion:SfListView.GroupHeaderTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <ViewCell.View>
                                <StackLayout>
                                    <Label Text="{Binding Key}" />
                                </StackLayout>
                            </ViewCell.View>
                        </ViewCell>
                    </DataTemplate>
                </syncfusion:SfListView.GroupHeaderTemplate>

for (i = 0; i < 5; i++) {
 setTimeout(function(m) {
    console.log(m);
 },i * 1000, i);
}

ListViewCargas.DataSource.GroupDescriptors.Add(new GroupDescriptor()
                {
                    PropertyName = "tramo",
                    KeySelector = (object obj1) =>
                    {
                        var item = (obj1 as cargasCarga);
                        return item.tramo + " - " + item.fechasalidatramo;
                    }

                });

-- Requires Ex. 3-1
DECLARE
  emp employee_typ; -- emp is atomically null
BEGIN
-- call the constructor for employee_typ
  emp := employee_typ(315, 'Francis', 'Logan', 'FLOGAN',
        '415.555.0100', '01-MAY-04', 'SA_MAN', 11000, .15, 101, 110,
         address_typ('376 Mission', 'San Francisco', 'CA', '94222'));
  DBMS_OUTPUT.PUT_LINE(emp.first_name || ' ' || emp.last_name); -- display details
  emp.display_address();  -- call object method to display details
END;
/

How PL/SQL Treats Uninitialized Objects

User-defined types, just like collections, are atomically null, until you initialize the object by calling the constructor for its object type. That is, the object itself is null, not just its attributes.

Comparing a null object with any other object always yields NULL. Also, if you assign an atomically null object to another object, the other object becomes atomically null (and must be reinitialized). Likewise, if you assign the non-value NULL to an object, the object becomes atomically null.