Expand and collapse icon in the group header of ListView

Expand and collapse the group when tapping icon in the group header item by customizing the SfListView.GroupHeaderTemplate with the help of converter.

<ContentPage xmlns:syncfusion="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms">
    <ContentPage.Resources>
        <ResourceDictionary>
            <local:BoolToImageConverter x:Key="BoolToImageConverter"/>
            <DataTemplate x:Name="GroupHeaderTemplate"  x:Key="GroupHeaderTemplate">
                <ViewCell>
                    <ViewCell.View>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="30" />
                                <ColumnDefinition Width="*" />
                            </Grid.ColumnDefinitions>
                            <Image x:Name="NormalImage" Grid.Column="0" HorizontalOptions="Center"
                                   Source="{Binding IsExpand, Converter={StaticResource BoolToImageConverter}}"
                                   VerticalOptions="Center"/>
                            <Label Text="{Binding Key}" Grid.Column="1"/>
                        </Grid>
                    </ViewCell.View>
                </ViewCell>
            </DataTemplate>
        </ResourceDictionary>
    </ContentPage.Resources>
    <ContentPage.Content>
        <Grid>
            <syncfusion:SfListView x:Name="listView" ItemSize="70"
                                 GroupHeaderSize="60"
                                 GroupHeaderTemplate="{StaticResource GroupHeaderTemplate}"
                                 ItemsSource="{Binding contactsInfo}"
                                 AllowGroupExpandCollapse="True">
            </syncfusion:SfListView>
        </Grid>
    </ContentPage.Content>
</ContentPage>

You can switch the expand or collapse group icon based on IsExpand property using the converter.

public class BoolToImageConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if ((bool)value) 
            return ImageSource.FromResource("ListViewSample.Images. GroupExpand.png");
        else
            return ImageSource.FromResource("ListViewSample.Images. GroupCollapse.png");
    }
  
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

To know more about the grouping in ListView, please refer our documentation here