Appearance customization of group header template

The User Interface (UI) for the group header items can be customized by using the SfListView.GroupHeaderTemplate property.

To customize the view for group header items and binding the Key to it, follow the code example.

<ContentPage xmlns:syncfusion="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms">
 <syncfusion:SfListView x:Name="listView">
  <syncfusion:SfListView.GroupHeaderTemplate>
    <DataTemplate>
      <ViewCell>
        <ViewCell.View>
          <StackLayout BackgroundColor="#E4E4E4">
            <Label Text="{Binding Key}"
                   FontSize="22"
                   FontAttributes="Bold"
                   VerticalOptions="Center"
                   HorizontalOptions="Start"
                   Margin="20,0,0,0" />
          </StackLayout>
        </ViewCell.View>
      </ViewCell>
    </DataTemplate>
  </syncfusion:SfListView.GroupHeaderTemplate>
 </syncfusion:SfListView>
</ContentPage>

To know more about grouping, please refer our documentation here