dictionary.txt

download from http://www.math.sjsu.edu/~foster/dictionary.txt

TypeAheadFormRx.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Reactive.Disposables;
using System.Reactive.Concurrency;
using System.Reactive.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TypeAheadComboWithRx
{
    public partial class Form1 : Form
    {
        public string[] words { get; set; }

        public Form1()
        {
            InitializeComponent();

            var sr = new System.IO.StreamReader("dictionary.txt");
            words = sr.ReadToEnd().Split('\n');
            sr.Close();

            //cmbTypeAhead.KeyDown
            var keydowns = Observable.FromEventPattern(k => cmbTypeAhead.TextChanged += k, k => cmbTypeAhead.TextChanged -= k);

            var observable = keydowns
                                .Select(b => cmbTypeAhead.Text)
                                .Do(b => DebugWrite(" before throttle .. " + b))
                                .Throttle(TimeSpan.FromMilliseconds(700))
                                .DistinctUntilChanged()
                                .Do(b => DebugWrite(" after throttle .. " + b))
                                .Select(b => 
                                    Observable.Create<IList<string>>(obs =>
                                    {
                                        obs.OnNext(GetResults(b).ToList());
                                        return Disposable.Empty;
                                    }).SubscribeOn(ThreadPoolScheduler.Instance));
            observable
                .Switch()
                .ObserveOn(new ControlScheduler(this))
                .Subscribe(a =>
                {
                    DebugWrite(" results " + a.Count);
                    cmbTypeAhead.DataSource = a;
                    cmbTypeAhead.DroppedDown = true;
                });

        }

        public void DebugWrite(string input)
        {
            var color = Console.ForegroundColor;
            Console.ForegroundColor = ConsoleColor.Gray;
            Console.WriteLine("{2} Thread: {0} .. {1}", System.Threading.Thread.CurrentThread.ManagedThreadId, input, DateTime.Now.ToLongTimeString());
            Console.ForegroundColor = color;
        }

        public IEnumerable<string> GetResults(string input)
        {
            DebugWrite("\t getting ... " + input);
            System.Threading.Thread.Sleep(10000);
            var matches = words.Where(s => s.StartsWith(input)).ToList();
            if (matches.Any() && matches.First() != input)
                matches.Insert(0, input);
            return matches;
        }

    }
}