How to change GroupHeader color based on theme in Xamarin.Forms ListView (SfListView)

The Xamarin.Forms SfListView allows you to apply light and dark theme using resource keys. You can find all the keys for SfListView control in this documentation. The ListViewItem background will be updated based on theme by default. For GroupHeaderItem, you can change the BackgroundColor using custom resource dictionary.

You can also refer the following article.

https://www.syncfusion.com/kb/11917/how-to-change-groupheader-color-based-on-theme-in-xamarin-forms-listview-sflistview

XAML

<Application xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:syncTheme="clr-namespace:Syncfusion.XForms.Themes;assembly=Syncfusion.Core.XForms"
             x:Class="ListViewXamarin.App">
    <Application.Resources>
        <syncTheme:SyncfusionThemeDictionary>
            <syncTheme:SyncfusionThemeDictionary.MergedDictionaries>
                <!-- Theme resource dictionary -->
                <syncTheme:DarkTheme />
                <ResourceDictionary>
                    <Color x:Key="GroupHeaderBackgroundColor">Red</Color>
                </ResourceDictionary>
            </syncTheme:SyncfusionThemeDictionary.MergedDictionaries>
        </syncTheme:SyncfusionThemeDictionary>
    </Application.Resources>
</Application>

XAML

To update the ListViewItem text color, bind SfListViewForegroundColor key to Label.TextColor property. For GroupHeaderItem, bind BackgroundColor of the element loaded in the GroupdHeaderTemplate with the custom group header resource key. Also, set the group header text color with SfListViewGroupHeaderForegroundColor key.

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:ListViewXamarin"
             xmlns:syncfusion="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms"
             x:Class="ListViewXamarin.MainPage">
    <ContentPage.BindingContext>
        <local:ContactsViewModel/>
    </ContentPage.BindingContext>
    
    <ContentPage.Behaviors>
        <local:Behavior/>
    </ContentPage.Behaviors>

    <ContentPage.Content>
        <StackLayout>
            <Button Text="Change theme" x:Name="ThemeButton"/>
            <syncfusion:SfListView x:Name="listView" ItemSize="60" ItemsSource="{Binding ContactsInfo}">
                <syncfusion:SfListView.ItemTemplate >
                    <DataTemplate>
                        <Grid x:Name="grid">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="70" />
                                <ColumnDefinition Width="*" />
                            </Grid.ColumnDefinitions>
                            <Image Source="{Binding ContactImage}" VerticalOptions="Center" HorizontalOptions="Center" HeightRequest="50" WidthRequest="50"/>
                            <Grid Grid.Column="1" RowSpacing="1" Padding="10,0,0,0" VerticalOptions="Center">
                                <Label LineBreakMode="NoWrap" TextColor="{DynamicResource SfListViewForegroundColor}" Text="{Binding ContactName}"/>
                                <Label Grid.Row="1" Grid.Column="0" TextColor="{DynamicResource SfListViewForegroundColor}" LineBreakMode="NoWrap" Text="{Binding ContactNumber}"/>
                            </Grid>
                        </Grid>
                    </DataTemplate>
                </syncfusion:SfListView.ItemTemplate>
                <syncfusion:SfListView.GroupHeaderTemplate>
                    <DataTemplate>
                        <StackLayout BackgroundColor="{DynamicResource GroupHeaderBackgroundColor}" >
                            <Label Text="{Binding Key}" FontSize="22" TextColor="{DynamicResource SfListViewGroupHeaderForegroundColor}" FontAttributes="Bold" VerticalOptions="Center" HorizontalOptions="Start" Margin="20,0,0,0" />
                        </StackLayout>
                    </DataTemplate>
                </syncfusion:SfListView.GroupHeaderTemplate>
            </syncfusion:SfListView>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

C#

In the Button.Clicked event, change the theme by removing the resource dictionary from the MergedResourceDictionary and add the new theme. Also, change the group header resource key value based on theme.

namespace ListViewXamarin
{
    public class Behavior : Behavior<ContentPage>
    {
        SfListView ListView;
        Button ThemeButton;
        protected override void OnAttachedTo(ContentPage bindable)
        {
            ListView = bindable.FindByName<SfListView>("listView");
            ThemeButton = bindable.FindByName<Button>("ThemeButton");
            ThemeButton.Clicked += ThemeButton_Clicked;

            base.OnAttachedTo(bindable);
        }

        private void ThemeButton_Clicked(object sender, EventArgs e)
        {
            ICollection<ResourceDictionary> mergedDictionaries = Application.Current.Resources.MergedDictionaries;
            var darkTheme = mergedDictionaries.OfType<DarkTheme>().FirstOrDefault();
            if (darkTheme != null)
            {
                mergedDictionaries.Remove(darkTheme);
                mergedDictionaries.Add(new LightTheme());
                var groupHeaderColor = mergedDictionaries.OfType<ResourceDictionary>().FirstOrDefault();
                groupHeaderColor["GroupHeaderBackgroundColor"] = Color.LightGray;
            }
            else
            {
                mergedDictionaries.Remove(mergedDictionaries.OfType<LightTheme>().FirstOrDefault());
                mergedDictionaries.Add(new DarkTheme());
                var groupHeaderColor = mergedDictionaries.OfType<ResourceDictionary>().FirstOrDefault();
                groupHeaderColor["GroupHeaderBackgroundColor"] = Color.Red;
            }
        }
    }
}

Output