Question

I have a richtextbox and inside I have a listbox. I would like the listbox to be positioned just underneath the caret and to move as the caret moves.

How can I do this?

Should I manipulate the first two values of listBox.Margin and how?
Thank you!

Answer 1

Here’s what I would do (replace my Rectangle with your ListBox):

<Window
    x:Class="Wpf_Playground.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow"
    Height="350"
    Width="525">
    <Grid>
        <RichTextBox
            Margin="0,0,0,32"
            x:Name="rtb"
            SpellCheck.IsEnabled="True"
            SelectionChanged="RtbSelectionChanged"
            TextChanged="RtbTextChanged">
        </RichTextBox>
        <Rectangle
            x:Name="rect"
            Width="30"
            Height="30"
            Fill="#80000000"
            VerticalAlignment="Top"
            HorizontalAlignment="Left"
            IsHitTestVisible="False"/>
        <TextBlock
            x:Name="tb"
            Margin="0"
            VerticalAlignment="Bottom" />
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;

namespace Wpf_Playground
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="MainWindow"/> class.
        /// </summary>
        public MainWindow()
        {
            InitializeComponent();
        }

        private void RtbSelectionChanged(object sender, RoutedEventArgs e)
        {
            this.UpdateCaretInfo();
        }

        /// <summary>
        /// The update caret info.
        /// </summary>
        private void UpdateCaretInfo()
        {
            var caretRect =
                rtb.CaretPosition.GetCharacterRect(LogicalDirection.Forward);
            tb.Text = caretRect.ToString();

            rect.Margin = new Thickness(
                caretRect.Right, 
                caretRect.Bottom, 
                -caretRect.Right, 
                -caretRect.Bottom);
        }

        private void RtbTextChanged(object sender, TextChangedEventArgs e)
        {
            this.UpdateCaretInfo();
        }
    }
}