WPF: Scroll Itemcontrol Content Fixed Header

Question

Is it possible to do something like this with WPF's ItemsControl: Demo

I am trying to freeze the GroupedItems rather than the GridView Columns.

Resources:

<Window.Resources>
    <CollectionViewSource x:Key="data" Source="{Binding}">
        <CollectionViewSource.GroupDescriptions>
            <PropertyGroupDescription PropertyName="Date"/>
        </CollectionViewSource.GroupDescriptions>
    </CollectionViewSource>
</Window.Resources>

ListView:

<ListView Grid.Column="0" ItemsSource="{Binding Source={StaticResource data}}">
    <ListView.View>
        <GridView>
            <GridView.Columns>
                <GridViewColumn Header="Col 1" DisplayMemberBinding="{Binding Col1}" Width="100"/>
                <GridViewColumn Header="Col 2" DisplayMemberBinding="{Binding Col2}" Width="100"/>
                <GridViewColumn Header="Col 3" DisplayMemberBinding="{Binding Col3}" Width="100"/>
            </GridView.Columns>
        </GridView>
    </ListView.View>
    <ListView.GroupStyle>
        <GroupStyle>
            <GroupStyle.ContainerStyle>
                <Style TargetType="{x:Type GroupItem}">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type GroupItem}">
                                <Grid>
                                    <Grid.RowDefinitions>
                                        <RowDefinition Height="Auto"/>
                                        <RowDefinition Height="Auto"/>
                                    </Grid.RowDefinitions>
                                    <Grid Grid.Row="0">
                                        <TextBlock Background="Beige" FontWeight="Bold" Text="{Binding Path=Name, StringFormat={}{0}}"/>
                                    </Grid>
                                    <DockPanel Grid.Row="1">
                                        <ItemsPresenter Grid.Row="2"></ItemsPresenter>
                                    </DockPanel>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </GroupStyle.ContainerStyle>
        </GroupStyle>
    </ListView.GroupStyle>
</ListView>

Code behind:

public MainWindow()
{
    InitializeComponent();

    List<String> colList1 = new List<string>() { "Item1", "Item2", "Item3", "Item4", "Item5", "Item6", "Item7" };
    List<String> colList2 = new List<string>() { "1", "2", "3", "4", "5", "6" };

    ObservableCollection<Data> dataCollection = new ObservableCollection<Data>();

    for (var a = 0; a < 100; a++)
    {
        Random rnd = new Random();
        int min = rnd.Next(5000);
        int rnd1 = rnd.Next(0, 6);
        int rnd2 = rnd.Next(0, 5);

        dataCollection.Add(new Data()
        {
            Date = DateTime.Now.AddMinutes(min).ToString("hh:MM tt"),
            Col1 = colList1[rnd2],
            Col2 = String.Format("Col2: {0}", "X"),
            Col3 = colList2[rnd2]
        });
    }
    this.DataContext = dataCollection;
}

public class Data
{
    public string Date { get; set; }
    public string Col1 { get; set; }
    public string Col2 { get; set; }
    public string Col3 { get; set; }
}

Answer 1

My solution uses a TextBlock overlay that shares the group header style. The positioning and correct HitTesting is the tricky part, but I'm quite confident this does not break for small changes in layout or logic.

I was not sure if you want to hide the ColumnHeader or not, but this is easy and doesn't need any other adjustments than what is depicted here.

Code behind:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace WpfApplication1
{
    public partial class FreezingGroupHeader : UserControl
    {
        private double _listviewHeaderHeight;
        private double _listviewSideMargin;

        public FreezingGroupHeader()
        {
            InitializeComponent();

            List<String> colList1 = new List<string>() { "Item1", "Item2", "Item3", "Item4", "Item5", "Item6", "Item7" };
            List<String> colList2 = new List<string>() { "1", "2", "3", "4", "5", "6" };

            ObservableCollection<Data> dataCollection = new ObservableCollection<Data>();

            Random rnd = new Random();

            for (var a = 0; a < 100; a++)
            {
                int min = rnd.Next(5000);
                int rnd1 = rnd.Next(0, 6);
                int rnd2 = rnd.Next(0, 5);

                dataCollection.Add(
                    new Data()
                    {
                        Date = DateTime.Now.AddMinutes(min).ToString("hh:MM tt"),
                        Col1 = colList1[rnd2],
                        Col2 = String.Format("Col2: {0}", "X"),
                        Col3 = colList2[rnd2]
                    }
                );
            }
            this.DataContext = dataCollection;

            this.Loaded += OnLoaded;
        }

        private void OnLoaded(object sender, RoutedEventArgs e)
        {
            // Position frozen header
            GetListViewMargins(this.listview1);

            Thickness margin = this.frozenGroupHeader.Margin;
            margin.Top = _listviewHeaderHeight;
            margin.Right = SystemParameters.VerticalScrollBarWidth + _listviewSideMargin;
            margin.Left = _listviewSideMargin;

            this.frozenGroupHeader.Margin = margin;

            UpdateFrozenGroupHeader();
        }

        private void listview1_ScrollChanged(object sender, ScrollChangedEventArgs e)
        {
            UpdateFrozenGroupHeader();
        }

        /// <summary>
        /// Sets text and visibility of frozen header
        /// </summary>
        private void UpdateFrozenGroupHeader()
        {
            if (listview1.HasItems)
            {
                // Text of frozenGroupHeader
                GroupItem group = GetFirstVisibleGroupItem(this.listview1);
                if (group != null)
                {
                    object data = group.Content;
                    this.frozenGroupHeader.Text = data.GetType().GetProperty("Name").GetValue(data, null) as string;  // slight hack
                }
                this.frozenGroupHeader.Visibility = Visibility.Visible;
            }
            else
                this.frozenGroupHeader.Visibility = Visibility.Collapsed;
        }

        /// <summary>
        /// Sets values that will be used in the positioning of the frozen header
        /// </summary>
        private void GetListViewMargins(ListView listview)
        {
            if (listview.HasItems)
            {
                object o = listview.Items[0];
                ListViewItem firstItem = (ListViewItem)listview.ItemContainerGenerator.ContainerFromItem(o);
                if (firstItem != null)
                {
                    GroupItem group = FindUpVisualTree<GroupItem>(firstItem);
                    Point p = group.TranslatePoint(new Point(0, 0), listview);
                    _listviewHeaderHeight = p.Y; // height of columnheader
                    _listviewSideMargin = p.X; // listview borders
                }
            }
        }

        /// <summary>
        /// Gets the first visible GroupItem in the listview
        /// </summary>
        private GroupItem GetFirstVisibleGroupItem(ListView listview)
        {
            HitTestResult hitTest = VisualTreeHelper.HitTest(listview, new Point(5, _listviewHeaderHeight + 5));
            GroupItem group = FindUpVisualTree<GroupItem>(hitTest.VisualHit);
            return group;
        }


        /// <summary>
        /// walk up the visual tree to find object of type T, starting from initial object
        /// http://www.codeproject.com/Tips/75816/Walk-up-the-Visual-Tree
        /// </summary>
        private static T FindUpVisualTree<T>(DependencyObject initial) where T : DependencyObject
        {
            DependencyObject current = initial;

            while (current != null && current.GetType() != typeof(T))
            {
                current = VisualTreeHelper.GetParent(current);
            }
            return current as T;
        }

        public class Data
        {
            public string Date { get; set; }
            public string Col1 { get; set; }
            public string Col2 { get; set; }
            public string Col3 { get; set; }
        }
    }
}

Xaml:

<UserControl x:Class="WpfApplication1.FreezingGroupHeader"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300"
           >

    <UserControl.Resources>
        <CollectionViewSource x:Key="data" Source="{Binding}">
            <CollectionViewSource.GroupDescriptions>
                <PropertyGroupDescription PropertyName="Date"/>
            </CollectionViewSource.GroupDescriptions>
        </CollectionViewSource>

        <Style x:Key="GroupHeaderStyle1" TargetType="{x:Type TextBlock}">
            <Setter Property="Background" Value="Beige" />
            <Setter Property="Foreground" Value="Black" />
            <Setter Property="FontWeight" Value="Bold" />
        </Style>
    </UserControl.Resources>

    <Grid>
        <ListView x:Name="listview1" Grid.Column="0" ItemsSource="{Binding Source={StaticResource data}}" ScrollViewer.ScrollChanged="listview1_ScrollChanged" >
            <ListView.View>
                <GridView>
                    <GridView.Columns>
                        <GridViewColumn Header="Col 1" DisplayMemberBinding="{Binding Col1}" Width="100"/>
                        <GridViewColumn Header="Col 2" DisplayMemberBinding="{Binding Col2}" Width="100"/>
                        <GridViewColumn Header="Col 3" DisplayMemberBinding="{Binding Col3}" Width="100"/>
                    </GridView.Columns>
                </GridView>
            </ListView.View>
            <ListView.GroupStyle>
                <GroupStyle>
                    <GroupStyle.ContainerStyle>
                        <Style TargetType="{x:Type GroupItem}">
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate TargetType="{x:Type GroupItem}">
                                        <Grid>
                                            <Grid.RowDefinitions>
                                                <RowDefinition  Height="Auto"/>
                                                <RowDefinition Height="Auto"/>
                                            </Grid.RowDefinitions>
                                            <Grid Grid.Row="0">
                                                <Grid.ColumnDefinitions>
                                                    <ColumnDefinition Width="*"/>
                                                </Grid.ColumnDefinitions>
                                                <TextBlock Style="{StaticResource GroupHeaderStyle1}" Text="{Binding Name, StringFormat={}{0}}"  />
                                            </Grid>
                                            <DockPanel Grid.Row="1">
                                                <ItemsPresenter Grid.Row="2"></ItemsPresenter>
                                            </DockPanel>
                                        </Grid>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </GroupStyle.ContainerStyle>
                </GroupStyle>
            </ListView.GroupStyle>
        </ListView>
        <TextBlock x:Name="frozenGroupHeader" Style="{StaticResource GroupHeaderStyle1}" VerticalAlignment="Top"/>
    </Grid>
</UserControl>