Aggregate summary

For each group, display the sum of values of the property from model object in the SfListView.GroupHeaderTemplate by using converter.

<ContentPage xmlns:syncfusion="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms"
             xmlns:data="clr-namespace:Syncfusion.DataSource;assembly=Syncfusion.DataSource.Portable">
  <syncfusion:SfListView x:Name="listView">
      <syncfusion:SfListView.GroupHeaderTemplate>
                    <DataTemplate x:Name="GroupHeaderTemplate"  x:Key="GroupHeaderTemplate">
                        <ViewCell>
                            <ViewCell.View>
                                <Grid BackgroundColor="#E4E4E4">
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="*" />
                                    </Grid.ColumnDefinitions>
                                    <Label Text="{Binding Key}" />
                                    <Label Text="{Binding Items,Converter={StaticResource Converter}}" Grid.Column="1" />
                                </Grid>
                            </ViewCell.View>
                        </ViewCell>
                    </DataTemplate>
      </syncfusion:SfListView.GroupHeaderTemplate>
  </syncfusion:SfListView>
</ContentPage>

To know more about grouping, please refer our documentation here