Set XAML ListBox MaxHeight to height of 10 rows

Question

How can I set the height (MaxHeight) of a ListBox to the height of a specified number of rows, such as 10? Either in XAML or in code-behind. This is for WPF.

It seems to be a very simple requirement and should be a common one but I cannot find anything to help. I cannot even find what the height is of the rows during execution.

Answer 1

<Window x:Class="Gekka.WpfApplication1.MainWindow2"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Gekka.WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow2" Height="400" Width="200">

    <DockPanel>
        <Slider x:Name="slider1" DockPanel.Dock="Bottom" Minimum="10" Value="20" Maximum="50" />

        <ListBox ItemsSource="{Binding}"
                 ScrollViewer.CanContentScroll="True" FontSize="8"
                 VerticalAlignment="Top">
            
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <local:VirtualizingStackPanelEx 
                        ViewCountLimit="10" 
                        Orientation="Vertical" />
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
            
            <ListBox.ItemContainerStyle>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Setter Property="Height" Value="{Binding ElementName=slider1,Path=Value}" />
                    <Setter Property="BorderBrush" Value="Black" />
                    <Setter Property="BorderThickness" Value="1" />
                    <Setter Property="Margin" Value="1" />
                </Style>
            </ListBox.ItemContainerStyle>
        </ListBox>
    </DockPanel>
</Window>

namespace Gekka.WpfApplication1
{
    using System;
    using System.Linq;
    using System.Windows;
    using System.Windows.Controls;

    public partial class MainWindow2 : Window
    {
        public MainWindow2()
        {
            InitializeComponent();

            this.DataContext = Enumerable.Range(1, 100).ToArray();
        }
    }

    class VirtualizingStackPanelEx : VirtualizingStackPanel
    {
        protected override Size ArrangeOverride(Size arrangeSize)
        {
            var sz = base.ArrangeOverride(arrangeSize);
            ArrangeScrollViewer();
            return sz;
        }

        private void ArrangeScrollViewer()
        {
            if (ScrollOwner == null)
            {
                return;
            }
            int count = 0;
            double length = 0;
            int limit = Math.Max(ViewCountLimit, 0);

            for (int i = 0; i < this.Children.Count && count < limit; i++)
            {
                if (this.Children[i] is FrameworkElement fe)
                {
                    var p = fe.TranslatePoint(new Point(0, 0), this);
                    if (this.Orientation == Orientation.Vertical)
                    {
                        if (p.Y >= 0)
                        {
                            length += fe.ActualHeight + fe.Margin.Top + fe.Margin.Bottom;
                            count++;
                        }
                    }
                    else
                    {
                        if (p.X >= 0)
                        {
                            length += fe.ActualWidth + fe.Margin.Left + fe.Margin.Right;
                            count++;
                        }
                    }
                }
            }

            if (this.Orientation == Orientation.Vertical)
            {
                ScrollOwner.MaxHeight = length;
                ScrollOwner.MaxWidth = double.PositiveInfinity;
            }
            else
            {
                ScrollOwner.MaxHeight = double.PositiveInfinity;
                ScrollOwner.MaxWidth = length;
            }
        }


        public int ViewCountLimit
        {
            get { return (int)GetValue(ViewCountLimitProperty); }
            set { SetValue(ViewCountLimitProperty, value); }
        }

        public static readonly DependencyProperty ViewCountLimitProperty
            = DependencyProperty.Register("ViewCountLimit", typeof(int), typeof(VirtualizingStackPanelEx)
                , new FrameworkPropertyMetadata((int)1, FrameworkPropertyMetadataOptions.AffectsArrange));
    }
}