URLComboBox: A Window Forms Control for Displaying URLs

using System;
using System.Windows.Forms;
using System.ComponentModel;
using Microsoft.Win32;

namespace CP.Windows.Forms
{
	/// <summary>
	/// A simple enumeration that wraps various auto complete flags of SHAutoComplete.
	/// See documenation of SHAutoComplete for details
	/// </summary>
	[Flags]
	public enum AutoCompleteFlags : int
	{
		/// <summary>
		/// This includes the File System as well as the rest of the shell (Desktop\My Computer\Control Panel\)
		/// </summary>
		FileSystem = 0x00000001,
		/// <summary>
		/// URLs in the User's History
		/// </summary>
		URLHistory = 0x00000002,
		/// <summary>
		/// URLs in the User's Recently Used list.
		/// </summary>
		URLMRU = 0x00000004,
		/// <summary>
		/// Use the tab to move thru the autocomplete possibilities instead of to the next dialog/window control.
		/// </summary>
		UseTab = 0x00000008,
		/// <summary>
		/// This includes the File System
		/// </summary>
		FileSystemOnly = 0x00000010,
		/// <summary>
		/// Same as FileSystemOnly except it only includes directories, UNC servers, and UNC server shares.
		/// </summary>
		FileSystemDirs = 0x00000020,
		/// <summary>
		/// Ignore the registry default and force the auto suggest feature on.
		/// </summary>
		AutoSuggestForceOn = 0x10000000,
		/// <summary>
		/// Ignore the registry default and force the auto suggest feature off
		/// </summary>
		AutoSuggestForceOff = 0x20000000,
		/// <summary>
		/// Ignore the registry default and force the auto append on. 
		/// </summary>
		AutoAppendForceOn = 0x40000000,
		/// <summary>
		/// Ignore the registry default and force auto append off. 
		/// </summary>
		AutoAppendForceOff = -2147483648
	}
	
	/// <summary>
	/// Enumeration for possible types of registry base keys for storing most recntly typed URLs
	/// </summary>
	public enum MRUKeyHive : int
	{
		/// <summary>
		/// Value that indicates HKEY_CURRENT_USER should be used for MRUKey property
		/// </summary>
		CurrentUser = 1,
		/// <summary>
		/// Value that indicates HKEY_LOCAL_MACHINE should be used for MRUKey property
		/// </summary>
		LocalMachine = 2,
	}

	/// <summary>
	/// A control that extends the regular combo box to show URLs.
	/// </summary>
	public class URLComboBox : ComboBox
	{
		/// <summary>
		/// Member variable which stores the autocomplete flags
		/// </summary>
		private AutoCompleteFlags _flags = AutoCompleteFlags.FileSystem | AutoCompleteFlags.URLHistory | AutoCompleteFlags.URLMRU;
		/// <summary>
		/// Member variable which stores the mru key
		/// </summary>
		private string _mruKey = @"Software\Microsoft\Internet Explorer\TypedURLs";
		/// <summary>
		/// Member variable which stores the mru key hive
		/// </summary>
		private MRUKeyHive _mruKeyHive = MRUKeyHive.CurrentUser;

		/// <summary>
		/// Initilaizes a new instance of URLComboBox
		/// </summary>
		public URLComboBox() : base()
		{
		}
		
		/// <summary>
		/// Gets the registry key where MRU URLs are stored
		/// </summary>
		/// <param name="writable">Indicates whether to get the key so that it values written to it</param>
		/// <returns>RegistryKey object for the MRU registry key or null if none exists</returns>
		private RegistryKey GetMRUKey(bool writable)
		{
			if (_mruKey.Length == 0)
				return null;

			RegistryKey ret = null;
			
			switch(_mruKeyHive)
			{
				case MRUKeyHive.LocalMachine:
					ret = Registry.LocalMachine.OpenSubKey(_mruKey, writable);
					break;
				case MRUKeyHive.CurrentUser:
					ret = Registry.CurrentUser.OpenSubKey(_mruKey, writable);
					break;
			}

			return ret;
		}
		
		/// <summary>
		/// Writes information about any ignored exception to the trace.
		/// </summary>
		/// <param name="e">The exception which is being ignored</param>
		private void TraceIgnoredError(Exception e)
		{
			//It's ok if there is any error
			System.Diagnostics.Trace.WriteLine(e.Message);
			System.Diagnostics.Trace.WriteLine(e.StackTrace);
		}
		
		/// <summary>
		/// Utility function to fill the combob box most recently typed URLs read from registry.
		/// </summary>
		private void MRUFill()
		{
			if (DesignMode)
				return;

			RegistryKey mruKey = null;

			try
			{
                int i = 1;

				string strFormat = "url{0}";
				object defaultValue = String.Empty;
				object url;
				
				mruKey = GetMRUKey(false);
				
				if (mruKey != null)
				{
					while((url = mruKey.GetValue(String.Format(strFormat, i), defaultValue)) != defaultValue)
					{
						Items.Add(url);
						i++;
					}
				}
			}
			catch(Exception e)
			{
				TraceIgnoredError(e);
			}
			finally
			{
				if (mruKey != null)
					mruKey.Close();
			}
		}

		/// <summary>
		/// Gets or sets the auto complete flags
		/// </summary>
		[Description("Gets or sets the auto complete flags")]
		public AutoCompleteFlags Flags
		{
			get
			{
				return _flags;
			}
			set
			{
				_flags = value;
			}
		}
		
		/// <summary>
		/// Gets or sets the registry key name where the combo box maintains MRU list.
		/// </summary>
		[DescriptionAttribute("The registry key name where the combo box maintains MRU list")]
		public string MRUKey
		{
			get
			{
				return _mruKey;
			}
			set
			{
				_mruKey = value;
			}
		}
		
		/// <summary>
		/// Gets or sets the registry key hive for the MRUKey property.
		/// </summary>
		[DescriptionAttribute("The registry hive where the combo box maintains MRU list")]
		public MRUKeyHive MRUKeyHive
		{
			get
			{
				return _mruKeyHive;
			}
			set
			{
				_mruKeyHive = value;
			}
		}

		/// <summary>
		/// Writes the recntly typed URL to the registry if it is not already there
		/// </summary>
		/// <param name="e"></param>
		protected override void OnValidated(System.EventArgs e)
		{
			if (DesignMode)
				return;

			if ((Text.Length != 0) && (Items.IndexOf(Text) == -1))
			{
				Items.Add(Text);
				
				RegistryKey mruKey = null;

				//Finally add it to the registry
				try
				{
					mruKey = GetMRUKey(true);
					
					if (mruKey != null)
						mruKey.SetValue(String.Format("url{0}", Items.Count), Text); 
				}
				catch(Exception ex)
				{
					TraceIgnoredError(ex);
				}
				finally
				{
					if (mruKey != null)
						mruKey.Close();
				}
			}
	
			base.OnValidated(e);
		}
		
		/// <summary>
		/// Finds the handle to the edit control and calls SHAutoComplete on it.
		/// Also fills the combobox from the values read from the registry
		/// </summary>
		/// <param name="e">Ignored</param>
		protected override void OnHandleCreated(System.EventArgs e)
		{
			base.OnHandleCreated(e);
			
			if (DesignMode)
				return;

			//This is the right place do auto completion
			ComboBoxInfo info = new ComboBoxInfo();
			info.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(info);

			if (UnManagedMethods.GetComboBoxInfo(Handle, ref info))
			{
				UnManagedMethods.SHAutoComplete(info.hwndEdit, (IntPtr)_flags);
			}
			
			MRUFill();
		}
	}
}