How to display a summary in the group header of Xamarin.Forms ListView (SfListView)?

You can display the summary of group items in the GroupHeader and update on the runtime changes in Xamarin.Forms SfListView.

You can also refer our artcile.

https://www.syncfusion.com/kb/12017/how-to-display-a-summary-in-the-group-header-of-xamarin-forms-listview-sflistview

XAML

Bind the GroupResult.Items property to the GroupHeader label and define the converter to display the aggregate summary.

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:ListViewXamarin"
             xmlns:listView="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms"
             xmlns:dataSource="clr-namespace:Syncfusion.DataSource;assembly=Syncfusion.DataSource.Portable"
             x:Class="ListViewXamarin.MainPage">
…
    <ContentPage.Resources>
        <ResourceDictionary>
            <local:SummaryConverter x:Key="Converter"/>
        </ResourceDictionary>
    </ContentPage.Resources>
    
    <ContentPage.Content>
        <Grid>
            <listView:SfListView x:Name="listView" ItemSize="70" GroupHeaderSize="60" ItemsSource="{Binding ContactsInfo}" ItemSpacing="0,0,5,0"> 
                <listView:SfListView.GroupHeaderTemplate>
                    <DataTemplate x:Name="GroupHeaderTemplate" >
                        <Grid BackgroundColor="#E4E4E4" Padding="10,0,0,0">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="Auto" />
                                <ColumnDefinition Width="*" />
                                <ColumnDefinition Width="50" />
                            </Grid.ColumnDefinitions>
                            <Label Text="Total: " FontSize="18" FontAttributes="Bold" VerticalOptions="Center"/>
                            <Label Text="{Binding Items, Converter={StaticResource Converter},StringFormat='{0:C2}'}" Grid.Column="1" FontSize="18"  FontAttributes="Bold" VerticalOptions="Center" HorizontalOptions="Start" Margin="0,0,0,0" />
                            <Grid Padding="5,5,5,5" Grid.Column="2">
                                <Label Text="+" FontSize="Large" HorizontalOptions="End" VerticalOptions="CenterAndExpand"/>
                                <Grid.GestureRecognizers>
                                    <TapGestureRecognizer Command="{Binding Path=BindingContext.AddItemCommand, Source={x:Reference listView}}" CommandParameter="{Binding .}"/>
                                </Grid.GestureRecognizers>
                            </Grid>
                        </Grid>
                    </DataTemplate>
                </listView:SfListView.GroupHeaderTemplate>
            </listView:SfListView>
        </Grid>
    </ContentPage.Content>
</ContentPage>

C#

Returns the total value of the group items based on the model property.

namespace ListViewXamarin
{
    public class SummaryConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            int result = 0;
            var items = value as IEnumerable;
            if(items != null)
            {
                var groupitems = items.ToList<object>().ToList<object>();
 
                if (groupitems != null)
                {
                    for (int i = 0; i < groupitems.Count; i++)
                    {
                        var contact = groupitems[i] as Contacts;
                        result += contact.Salary;
                    }
                }
            }
            return result;
        }
    }
}

C#

In the ItemTapped event, update the model property value of the item. To reflect the changes in the GroupHeader, refresh the GroupHeader by setting the BindingContext as null. You can get the GroupResult of the tapped item from the ListView.DataSource.DisplayItems property.

namespace ListViewXamarin
{
   public class Behavior : Behavior<ContentPage>
    {
        SfListView ListView;
 
        protected override void OnAttachedTo(ContentPage bindable)
        {
            ListView = bindable.FindByName<SfListView>("listView");
            ...
            ListView.DataSource.GroupDescriptors.Add(new GroupDescriptor()
            {
                PropertyName = "ContactType",
            });
            ListView.ItemTapped += ListView_ItemTapped;
            base.OnAttachedTo(bindable);
        }
 
        private void ListView_ItemTapped(object sender, Syncfusion.ListView.XForms.ItemTappedEventArgs e)
        {
            if (e.ItemType == ItemType.Record)
            {
                (e.ItemData as Contacts).Salary += 100;
                var groupResult = this.GetGroup(e.ItemData);
                this.RefreshGroupHeader(groupResult);
                ListView.RefreshView();
            }
        } 
 
        public GroupResult GetGroup(object itemData)
        {
            GroupResult itemGroup = null;
 
            foreach (var item in this.ListView.DataSource.DisplayItems)
            {
                if (item == itemData)
                    break;
 
                if (item is GroupResult)
                    itemGroup = item as GroupResult;
            }
            return itemGroup;
        }
 
        private void RefreshGroupHeader(GroupResult group)
        {
            foreach (var item in ListView.GetVisualContainer().Children)
            {
                if (item.BindingContext == group)
                {
                    item.BindingContext = null;
                    (item as GroupHeaderItem).Content.BindingContext = null;
                }
            }
        }
    }
}

You can get the GroupHeaderItem from the VisualContainer and set the GroupHeaderItem.BindingContext and BindingContext of the element loaded in the GroupHeader to null. You can access the VisualContainer using the GetVisualContainer method. And refresh the ListView using the RefreshView method to update the changes to the UI.

Output