c# combobox autocomplete behavior

using System;
using System.Data;
using System.Linq;
using System.Windows.Forms;

namespace EE_Q28966499
{
	public partial class Form1 : Form
	{
		public Form1()
		{
			InitializeComponent();
		}

		private void OnLoad(object sender, EventArgs e)
		{
			DataSet set = new DataSet();
			set.Tables.Add((from i in Enumerable.Range(0, 20) select new { ID = i, FirstName = string.Format("{0}{1}", i % 5 == 0 ? "John" : i % 4 == 0 ? "Mary" : i % 3 == 0 ? "Paul" : i % 2 == 0 ? "Clarence" : "MaryJo", i), Birthdate = DateTime.Now.AddYears(-(9 * i)), IsWorking = (i & 1) == 0 }).ConvertToDataTable("AllPeople"));
			comboBox1.DataSource = set.Tables["AllPeople"].DefaultView;
			comboBox1.DisplayMember = "FirstName";
			comboBox1.PropertySelector = c => c.Cast<DataRowView>().Select(view => view["FirstName"].ToString());
			comboBox1.FilterRule = (item, text) => item.IndexOf(text.Trim(), StringComparison.OrdinalIgnoreCase) > -1;
		}

		private void OnKeyPress(object sender, KeyPressEventArgs e)
		{
			if (sender is ComboBox)
			{
				var cmb = sender as ComboBox;
				if (cmb.Equals(comboBox1) && cmb.SelectedItem != null)
				{
					listBox1.Items.Add((cmb.SelectedItem as DataRowView).Row["FirstName"].ToString());
				}
			}
		}
	}
}

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namespace EE_Q28966499
{
	partial class Form1
	{
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.IContainer components = null;

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
		protected override void Dispose(bool disposing)
		{
			if (disposing && (components != null))
			{
				components.Dispose();
			}
			base.Dispose(disposing);
		}

		#region Windows Form Designer generated code

		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			this.comboBox1 = new EE_Q28966499.AutoCompleteComboBox();
			this.listBox1 = new System.Windows.Forms.ListBox();
			this.SuspendLayout();
			// 
			// comboBox1
			// 
			this.comboBox1.FilterRule = null;
			this.comboBox1.FormattingEnabled = true;
			this.comboBox1.Location = new System.Drawing.Point(13, 13);
			this.comboBox1.Name = "comboBox1";
			this.comboBox1.PropertySelector = null;
			this.comboBox1.Size = new System.Drawing.Size(259, 21);
			this.comboBox1.SuggestionBoxHeight = 96;
			this.comboBox1.SuggestionListOrderRule = null;
			this.comboBox1.TabIndex = 0;
			this.comboBox1.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.OnKeyPress);
			// 
			// listBox1
			// 
			this.listBox1.FormattingEnabled = true;
			this.listBox1.Location = new System.Drawing.Point(13, 41);
			this.listBox1.Name = "listBox1";
			this.listBox1.Size = new System.Drawing.Size(259, 212);
			this.listBox1.TabIndex = 1;
			// 
			// Form1
			// 
			this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
			this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
			this.ClientSize = new System.Drawing.Size(284, 261);
			this.Controls.Add(this.listBox1);
			this.Controls.Add(this.comboBox1);
			this.Name = "Form1";
			this.Text = "Form1";
			this.Load += new System.EventHandler(this.OnLoad);
			this.ResumeLayout(false);

		}

		#endregion

		private AutoCompleteComboBox comboBox1;
		private System.Windows.Forms.ListBox listBox1;
	}
}

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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Linq.Expressions;
using System.Windows.Forms;

namespace EE_Q28966499
{
	static class Extensions
	{
		public static DataTable ConvertToDataTable<T>(this IEnumerable<T> source, string name = "")
		{
			DataTable table = string.IsNullOrWhiteSpace(name) ? new DataTable() : new DataTable(name);
			var properties = TypeDescriptor.GetProperties(typeof(T));
			foreach (PropertyDescriptor property in properties)
			{
				if (property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
					table.Columns.Add(property.Name, property.PropertyType.GetGenericArguments()[0]);
				else
					table.Columns.Add(property.Name, property.PropertyType);
			}

			object[] values = new object[properties.Count];
			foreach (var item in source)
			{
				for (int i = 0; i < properties.Count; i++)
					values[i] = properties[i].GetValue(item);
				table.Rows.Add(values);
			}
			return table;
		}
	}

	// Credit to PhysIcu$ for source - http://www.codeproject.com/Tips/631196/ComboBox-with-Suggest-Ability-based-on-Substring-S
	public sealed class AutoCompleteComboBox : ComboBox
	{
		#region fields and properties
		private readonly ListBox _suggestionBox = new ListBox { Visible = false, TabStop = false };
		private readonly BindingList<string> _suggestions = new BindingList<string>();
		private Expression<Func<ObjectCollection, IEnumerable<string>>> _propertySelector;
		private Func<ObjectCollection, IEnumerable<string>> _propertySelectorCompiled;
		private Expression<Func<string, string, bool>> _filterRule;
		private Func<string, bool> _filterRuleCompiled;
		private Expression<Func<string, string>> _suggestListOrderRule;
		private Func<string, string> _suggestListOrderRuleCompiled;

		/// <summary>Gets or sets the height of the suggestion box.</summary>
		/// <value>The height of the suggestion box.</value>
		public int SuggestionBoxHeight
		{
			get { return _suggestionBox.Height; }
			set
			{
				if (value > 0)
					_suggestionBox.Height = value;
			}
		}

		/// <summary>If the item-type of the ComboBox is not string, you can set here which property should be used</summary>
		public Expression<Func<ObjectCollection, IEnumerable<string>>> PropertySelector
		{
			get { return _propertySelector; }
			set
			{
				if (value == null) return;
				_propertySelector = value;
				_propertySelectorCompiled = value.Compile();
			}
		}

		///<summary>Lambda-Expression to determine the suggested items
		/// (as Expression here because simple lamda (func) is not serializable)
		/// <para>default: case-insensitive contains search</para>
		/// <para>1st string: list item</para>
		/// <para>2nd string: typed text</para>
		///</summary>
		public Expression<Func<string, string, bool>> FilterRule
		{
			get { return _filterRule; }
			set
			{
				if (value == null) return;
				_filterRule = value;
				_filterRuleCompiled = item => value.Compile()(item, Text);
			}
		}

		///<summary>
		/// Lambda-Expression to order the suggested items
		/// (as Expression here because simple lamda (func) is not serializable)
		/// <para>default: alphabetic ordering</para>
		///</summary>
		public Expression<Func<string, string>> SuggestionListOrderRule
		{
			get { return _suggestListOrderRule; }
			set
			{
				if (value == null) return;
				_suggestListOrderRule = value;
				_suggestListOrderRuleCompiled = value.Compile();
			}
		}

		#endregion

		/// <summary>Initializes a new instance of the <see cref="AutoCompleteComboBox"/> class.</summary>
		public AutoCompleteComboBox()
		{
			// set the standard rules:
			_filterRuleCompiled = s => s.ToLower().Contains(Text.Trim().ToLower());
			_suggestListOrderRuleCompiled = s => s;
			_propertySelectorCompiled = collection => collection.Cast<string>();

			_suggestionBox.DataSource = _suggestions;
			_suggestionBox.Click += OnClick;

			ParentChanged += OnParentChanged;
		}

		/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.TextChanged" /> event.</summary>
		/// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
		protected override void OnTextChanged(EventArgs e)
		{
			base.OnTextChanged(e);

			if (!Focused) return;

			_suggestions.Clear();
			_suggestions.RaiseListChangedEvents = false;
			_propertySelectorCompiled(Items)
				.Where(_filterRuleCompiled)
				.OrderBy(_suggestListOrderRuleCompiled)
				.ToList()
				.ForEach(_suggestions.Add);
			_suggestions.RaiseListChangedEvents = true;
			_suggestions.ResetBindings();

			_suggestionBox.Visible = _suggestions.Any();

			if (_suggestions.Count == 1 &&
						_suggestions.Single().Length == Text.Trim().Length)
			{
				Text = _suggestions.Single();
				Select(0, Text.Length);
				_suggestionBox.Visible = false;
			}
		}

		#region size and position of suggest box

		/// <summary>Handles the <see cref="E:ParentChanged" /> event.</summary>
		/// <param name="sender">The sender.</param>
		/// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
		private void OnParentChanged(object sender, EventArgs e)
		{
			Parent.Controls.Add(_suggestionBox);
			Parent.Controls.SetChildIndex(_suggestionBox, 0);
			_suggestionBox.Top = Top + Height - 3;
			_suggestionBox.Left = Left + 3;
			_suggestionBox.Width = Width - 20;
			_suggestionBox.Font = new Font("Segoe UI", 9);
		}

		/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.LocationChanged" /> event.</summary>
		/// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
		protected override void OnLocationChanged(EventArgs e)
		{
			base.OnLocationChanged(e);
			_suggestionBox.Top = Top + Height - 3;
			_suggestionBox.Left = Left + 3;
		}

		/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.SizeChanged" /> event.</summary>
		/// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
		protected override void OnSizeChanged(EventArgs e)
		{
			base.OnSizeChanged(e);
			_suggestionBox.Width = Width - 20;
		}

		#endregion

		#region visibility of suggest box

		/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.LostFocus" /> event.</summary>
		/// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
		protected override void OnLostFocus(EventArgs e)
		{
			// _suggLb can only getting focused by clicking (because TabStop is off)
			// --> click-eventhandler 'SuggLbOnClick' is called
			if (!_suggestionBox.Focused)
				HideSuggestionBox();
			base.OnLostFocus(e);
		}

		/// <summary>Handles the <see cref="E:Click" /> event.</summary>
		/// <param name="sender">The sender.</param>
		/// <param name="eventArgs">The <see cref="EventArgs"/> instance containing the event data.</param>
		private void OnClick(object sender, EventArgs eventArgs)
		{
			Text = _suggestionBox.Text;
			Focus();
		}

		/// <summary>Hides the suggestion box.</summary>
		private void HideSuggestionBox()
		{
			_suggestionBox.Visible = false;
		}

		/// <summary>Raises the <see cref="E:System.Windows.Forms.ComboBox.DropDown" /> event.</summary>
		/// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
		protected override void OnDropDown(EventArgs e)
		{
			HideSuggestionBox();
			base.OnDropDown(e);
		}

		#endregion

		#region keystroke events

		/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.PreviewKeyDown" /> event.</summary>
		/// <param name="e">A <see cref="T:System.Windows.Forms.PreviewKeyDownEventArgs" /> that contains the event data.</param>
		protected override void OnPreviewKeyDown(PreviewKeyDownEventArgs e)
		{
			if (!_suggestionBox.Visible)
			{
				base.OnPreviewKeyDown(e);
				return;
			}

			switch (e.KeyCode)
			{
				case Keys.Down:
					if (_suggestionBox.SelectedIndex < _suggestions.Count - 1)
						_suggestionBox.SelectedIndex++;
					return;
				case Keys.Up:
					if (_suggestionBox.SelectedIndex > 0)
						_suggestionBox.SelectedIndex--;
					return;
				case Keys.Enter:
					Text = _suggestionBox.Text;
					Select(0, Text.Length);
					_suggestionBox.Visible = false;
					return;
				case Keys.Escape:
					HideSuggestionBox();
					return;
			}

			base.OnPreviewKeyDown(e);
		}

		/// <summary>The keys to handle</summary>
		private static readonly Keys[] KeysToHandle = new[] { Keys.Down, Keys.Up, Keys.Enter, Keys.Escape };

		/// <summary>Processes a command key.</summary>
		/// <param name="msg">A <see cref="T:System.Windows.Forms.Message" />, passed by reference, that represents the window message to process.</param>
		/// <param name="keyData">One of the <see cref="T:System.Windows.Forms.Keys" /> values that represents the key to process.</param>
		/// <returns>true if the character was processed by the control; otherwise, false.</returns>
		protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
		{
			// the keysstrokes of our interest should not be processed be base class:
			if (_suggestionBox.Visible && KeysToHandle.Contains(keyData))
				return true;
			return base.ProcessCmdKey(ref msg, keyData);
		}
		#endregion
	}
}

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