Autocomplete in Silverlight

<TextBox x:Name="uiText" Width="100" Height="30"
    manas:Autocomplete.Suggest="DoSuggest" />

// The texts we want to suggest
private string[] options = new string[]
{
    "Al", "Amiko", "Angla", "Anglujo", "Ankaux", "Antaux", "Atomo", "Auxto",
    "Bebo", "Bela", "Birdo",
}

// The method we have to implement to offer suggestions
public void DoSuggest(string text, SuggestCallback callback)
{
    // Don't suggest if there's no text
    if (text.Length == 0)
    {
        callback(null);
        return;
    }

    var result = new List();

    // See which options have as a prefix the text entered by the user
    foreach (var option in options)
    {
        if (option.StartsWith(text, StringComparison.InvariantCultureIgnoreCase))
        {
            result.Add(new Suggestion() { DisplayString = option,
                                                      ReplaceString = option });
        }
    }

    callback(result.ToArray());
}

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Diagnostics;

namespace Manas.Silverlight
{

    /// <summary>
    /// Allows reporting suggestions asynchronously.
    /// </summary>
    public delegate void SuggestCallback(Suggestion[] suggestions);

    /// <summary>
    /// Invoked when suggestions are needed.
    /// </summary>
    /// <param name="text">the text to autocomplete</param>
    /// <param name="callback">where to report the suggestions</param>
    public delegate void SuggestHandler(string text, SuggestCallback callback);

    /// <summary>
    /// Each suggestion to report for the autocompletion.
    /// </summary>
    public class Suggestion
    {

        /// <summary>
        /// What to show in the autocomplete popup.
        /// </summary>
        public string DisplayString { get; set; }

        /// <summary>
        /// What to insert as a replacement if this suggestion is selected.
        /// </summary>
        public string ReplaceString { get; set; }

        public override string ToString()
        {
            return DisplayString;
        }

    }

    /// <summary>
    /// Allows adding autocomplete capabilities to a TextBox.
    /// </summary>
    public class Autocomplete
    {

        #region XAML support
        public static readonly DependencyProperty Suggest = DependencyProperty.RegisterAttached("Suggest", typeof(string), typeof(Autocomplete), null);

        public static void SetSuggest(DependencyObject obj, string handler)
        {
            obj.SetValue(Suggest, handler);

            EventSupport.AttachEvent(obj, handler,
                new Type[] { typeof(string), typeof(SuggestCallback) },
                (sender, target, info) =>
                {
                    Autocomplete autocomplete = new Autocomplete(sender as TextBox);
                    autocomplete.SuggestHandler = (text, callback) =>
                    {
                        info.Invoke(target, new object[] { text, callback });
                    };
                });
        }

        public static string GetSuggest(DependencyObject obj)
        {
            return (string)obj.GetValue(Suggest);
        }
        #endregion

        private TextBox textBox;
        private ListBox listBox;

        internal Autocomplete(TextBox textBox)
        {
            this.textBox = textBox;

            textBox.LostFocus += textBox_LostFocus;
            textBox.GotFocus += (s, e) =>
            {
                OfferSuggestions();
            };
            textBox.KeyDown += textBox_KeyDown;
            textBox.KeyUp += textBlock_KeyUp;
        }

        /// <summary>
        /// Adds autocomplete support to the given TextBox.
        /// </summary>
        public Autocomplete(TextBox textBox, SuggestHandler handler)
            : this(textBox)
        {
            this.SuggestHandler = handler;
        }

        internal SuggestHandler SuggestHandler { get; set; }

        void textBox_LostFocus(object sender, RoutedEventArgs e)
        {
            object elem = FocusManager.GetFocusedElement();
            if (elem == listBox)
            {
                return;
            }

            ListBoxItem item = elem as ListBoxItem;
            if (item != null)
            {
                object parent = item.Parent;
                while (!(parent is ListBox) && parent is FrameworkElement)
                {
                    parent = (parent as FrameworkElement).Parent;
                }

                if (parent == listBox)
                {
                    InsertSuggestion();
                }
            }

            HideListBox();
        }

        void textBox_KeyDown(object sender, KeyEventArgs e)
        {
            if (listBox == null) return;

            if (e.Key == Key.Down)
            {
                listBox.SelectedIndex = (listBox.SelectedIndex + 1) % listBox.Items.Count;
            }
            else if (e.Key == Key.Up)
            {
                if (listBox.SelectedIndex == 0)
                {
                    listBox.SelectedIndex = listBox.Items.Count - 1;
                }
                else
                {
                    listBox.SelectedIndex--;
                }
            }
            else if (e.Key == Key.Enter)
            {
                InsertSuggestion();
            }
        }

        void textBlock_KeyUp(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Down || e.Key == Key.Up) return;

            OfferSuggestions();
        }

        void OfferSuggestions()
        {
            SuggestHandler(textBox.Text, Callback);
        }

        void Callback(Suggestion[] suggestions)
        {
            // If there are no suggestions, do nothing
            //                    or
            // If there is only one suggestion but it's the text that we have in the
            // text box, do nothing
            if (suggestions == null ||
                suggestions.Length == 0 ||
                (suggestions.Length == 1 && suggestions[0].ReplaceString == textBox.Text))
            {
                HideListBox();
                return;
            }

            ShowListBox(suggestions.Length);

            listBox.Items.Clear();
            foreach (var suggestion in suggestions)
            {
                listBox.Items.Add(suggestion);
            }

            this.listBox.Dispatcher.BeginInvoke(() =>
            {
                listBox.SelectedIndex = 0;
            });
        }

        void ShowListBox(int count)
        {
            if (listBox == null)
            {
                listBox = new ListBox();
                ScrollViewer.SetVerticalScrollBarVisibility(listBox, ScrollBarVisibility.Visible);
                listBox.SelectionChanged += (s, e) =>
                {
                    if (listBox.SelectedItem != null && listBox.Items.Contains(listBox.SelectedItem))
                    {
                        try
                        {
                            listBox.ScrollIntoView(listBox.SelectedItem);
                        }
                        catch { }
                    }
                };
                listBox.MinWidth = textBox.RenderSize.Width;

                var canvas = (Canvas)System.Windows.Application.Current.RootVisual;
                var transform = textBox.TransformToVisual(canvas);
                var topLeft = transform.Transform(new Point(0, 0));

                Canvas.SetLeft(listBox, topLeft.X);
                Canvas.SetTop(listBox, topLeft.Y + textBox.RenderSize.Height);
                canvas.Children.Add(listBox);
            }

            if (count >= 5)
            {
                count = 5;
            }
            listBox.MaxHeight = count * 21;
        }

        private void InsertSuggestion()
        {
            Suggestion suggestion = listBox.SelectedItem as Suggestion;
            if (suggestion != null)
            {
                textBox.Text = suggestion.ReplaceString;
                textBox.Select(textBox.Text.Length, 0);
            }
        }

        void HideListBox()
        {
            if (listBox != null)
            {
                var canvas = (Canvas)System.Windows.Application.Current.RootVisual;
                canvas.Children.Remove(listBox);
                listBox = null;
            }
        }

    }

}