C# does Shell, Part 4

using System;
using System.Runtime.InteropServices;

namespace ShellLib
{
	public class ShellBrowseForFolderDialog
	{
		// The SendMessage function sends the specified message to a window or windows. It calls the window procedure for 
		// the specified window and does not return until the window procedure has processed the message. 
		[DllImport("User32.dll")]
		public static extern Int32 SendMessage(
			IntPtr hWnd,			// handle to destination window
			UInt32 Msg,				// message
			UInt32 wParam,			// first message parameter
			Int32 lParam			// second message parameter
			);

		[DllImport("User32.dll")]
		public static extern Int32 SendMessage(
			IntPtr hWnd,			// handle to destination window
			UInt32 Msg,				// message
			UInt32 wParam,			// first message parameter
			[MarshalAs(UnmanagedType.LPWStr)]
			String lParam			// second message parameter
			);

		public enum RootTypeOptions
		{
			BySpecialFolder,
			ByPath
		}

		[Flags]
		public enum BrowseInfoFlag // BIF
		{
			BIF_RETURNONLYFSDIRS   = 0x0001,	// For finding a folder to start document searching
			BIF_DONTGOBELOWDOMAIN  = 0x0002,	// For starting the Find Computer
			BIF_STATUSTEXT         = 0x0004,	// Top of the dialog has 2 lines of text for BROWSEINFO.lpszTitle and 
			// one line if this flag is set.  Passing the message 
			// BFFM_SETSTATUSTEXTA to the hwnd can set the rest of the text.  
			// This is not used with BIF_USENEWUI and BROWSEINFO.lpszTitle gets
			// all three lines of text.
			BIF_RETURNFSANCESTORS  = 0x0008,
			BIF_EDITBOX            = 0x0010,	// Add an editbox to the dialog
			BIF_VALIDATE           = 0x0020,	// insist on valid result (or CANCEL)
			BIF_NEWDIALOGSTYLE     = 0x0040,	// Use the new dialog layout with the ability to resize
			// Caller needs to call OleInitialize() before using this API
			BIF_USENEWUI           = (BIF_NEWDIALOGSTYLE | BIF_EDITBOX),
			BIF_BROWSEINCLUDEURLS  = 0x0080,    // Allow URLs to be displayed or entered. (Requires BIF_USENEWUI)
			BIF_UAHINT             = 0x0100,    // Add a UA hint to the dialog, in place of the edit box. May not be 
			// combined with BIF_EDITBOX
			BIF_NONEWFOLDERBUTTON  = 0x0200,    // Do not add the "New Folder" button to the dialog.  Only applicable 
			// with BIF_NEWDIALOGSTYLE.
			BIF_NOTRANSLATETARGETS = 0x0400,    // don't traverse target as shortcut
			BIF_BROWSEFORCOMPUTER  = 0x1000,	// Browsing for Computers.
			BIF_BROWSEFORPRINTER   = 0x2000,	// Browsing for Printers
			BIF_BROWSEINCLUDEFILES = 0x4000,	// Browsing for Everything
			BIF_SHAREABLE          = 0x8000		// sharable resources displayed (remote shares, requires BIF_USENEWUI)
		}

		public enum	BrowseForFolderMessages	// BFFM
		{
			// message from browser
			BFFM_INITIALIZED        = 1,
			BFFM_SELCHANGED         = 2,
			BFFM_VALIDATEFAILEDA    = 3,				// lParam:szPath ret:1(cont),0(EndDialog)
			BFFM_VALIDATEFAILEDW    = 4,				// lParam:wzPath ret:1(cont),0(EndDialog)
			BFFM_IUNKNOWN           = 5, 				// provides IUnknown to client. lParam: IUnknown*

			// messages to browser
			// 0x400 = WM_USER
			BFFM_SETSTATUSTEXTA     = (0x0400 + 100),
			BFFM_ENABLEOK           = (0x0400 + 101),
			BFFM_SETSELECTIONA      = (0x0400 + 102),
			BFFM_SETSELECTIONW      = (0x0400 + 103),
			BFFM_SETSTATUSTEXTW     = (0x0400 + 104),
			BFFM_SETOKTEXT          = (0x0400 + 105),	// Unicode only
			BFFM_SETEXPANDED        = (0x0400 + 106)	// Unicode only
		}

		public class InitializedEventArgs : EventArgs
		{
			public InitializedEventArgs(IntPtr hwnd)
			{
				this.hwnd = hwnd;
			}
			public readonly IntPtr hwnd;
		}

		public class IUnknownEventArgs : EventArgs
		{
			public IUnknownEventArgs(IntPtr hwnd, IntPtr iunknown)
			{
				this.hwnd = hwnd;
				this.iunknown = iunknown;
			}
			public readonly IntPtr hwnd;
			public readonly IntPtr iunknown;
		}

		public class SelChangedEventArgs : EventArgs
		{
			public SelChangedEventArgs(IntPtr hwnd, IntPtr pidl)
			{
				this.hwnd = hwnd;
				this.pidl = pidl;
			}
			public readonly IntPtr hwnd;
			public readonly IntPtr pidl;
		}

		public class ValidateFailedEventArgs : EventArgs
		{
			public ValidateFailedEventArgs(IntPtr hwnd, string invalidSel)
			{
				this.hwnd = hwnd;
				this.invalidSel = invalidSel;
			}
			public readonly IntPtr hwnd;
			public readonly string invalidSel;
		}
		
		
		public delegate void InitializedHandler(ShellBrowseForFolderDialog sender, InitializedEventArgs args);
		public delegate void IUnknownHandler(ShellBrowseForFolderDialog sender, IUnknownEventArgs args);
		public delegate void SelChangedHandler(ShellBrowseForFolderDialog sender, SelChangedEventArgs args);
		public delegate int ValidateFailedHandler(ShellBrowseForFolderDialog sender, ValidateFailedEventArgs args);  

		public event InitializedHandler OnInitialized;
		public event IUnknownHandler OnIUnknown;
		public event SelChangedHandler OnSelChanged;
		public event ValidateFailedHandler OnValidateFailed;

		public void EnableOk(IntPtr hwnd, bool Enabled)
		{
			SendMessage(hwnd, (uint)BrowseForFolderMessages.BFFM_ENABLEOK, 0, Enabled ? 1 : 0); 
		}

		public void SetExpanded(IntPtr hwnd, string path)
		{
			SendMessage(hwnd, (uint)BrowseForFolderMessages.BFFM_SETEXPANDED, 1, path);
		}

		public void SetOkText(IntPtr hwnd, string text)
		{
			SendMessage(hwnd, (uint)BrowseForFolderMessages.BFFM_SETOKTEXT, 0, text);
		}

		public void SetSelection(IntPtr hwnd, string path)
		{
			SendMessage(hwnd, (uint)BrowseForFolderMessages.BFFM_SETSELECTIONW, 1, path);
		}

		public void SetStatusText(IntPtr hwnd, string text)
		{
			SendMessage(hwnd, (uint)BrowseForFolderMessages.BFFM_SETSTATUSTEXTW, 1, text);
		}


		private Int32 myBrowseCallbackProc(IntPtr hwnd, UInt32 uMsg, Int32 lParam, Int32 lpData)
		{
			switch ((BrowseForFolderMessages)uMsg)
			{
				case BrowseForFolderMessages.BFFM_INITIALIZED:
					System.Diagnostics.Debug.WriteLine("BFFM_INITIALIZED");

					if (OnInitialized != null)
					{
						InitializedEventArgs args = new InitializedEventArgs(hwnd);
						OnInitialized(this,args);
					}

					break;

				case BrowseForFolderMessages.BFFM_IUNKNOWN:
					System.Diagnostics.Debug.WriteLine("BFFM_IUNKNOWN");

					if (OnIUnknown != null)
					{
						IUnknownEventArgs args = new IUnknownEventArgs(hwnd,(IntPtr)lParam);
						OnIUnknown(this,args);
					}

					break;

				case BrowseForFolderMessages.BFFM_SELCHANGED:
					System.Diagnostics.Debug.WriteLine("BFFM_SELCHANGED");
					
					if (OnSelChanged != null)
					{
						SelChangedEventArgs args = new SelChangedEventArgs(hwnd,(IntPtr)lParam);
						OnSelChanged(this,args);
					}
				
					break;
				
				case BrowseForFolderMessages.BFFM_VALIDATEFAILEDA:
					System.Diagnostics.Debug.WriteLine("BFFM_VALIDATEFAILEDA");
				
					if (OnValidateFailed != null)
					{
						string failedSel = Marshal.PtrToStringAnsi((IntPtr)lParam);
						ValidateFailedEventArgs args = new ValidateFailedEventArgs(hwnd,failedSel);
						return OnValidateFailed(this,args);
					}
					break;

				case BrowseForFolderMessages.BFFM_VALIDATEFAILEDW:
					System.Diagnostics.Debug.WriteLine("BFFM_VALIDATEFAILEDW");
					
					if (OnValidateFailed != null)
					{
						string failedSel = Marshal.PtrToStringUni((IntPtr)lParam);
						ValidateFailedEventArgs args = new ValidateFailedEventArgs(hwnd,failedSel);
						return OnValidateFailed(this,args);
					}
										
					break;
			}

			return 0;
		}


		public ShellBrowseForFolderDialog()
		{
			hwndOwner = IntPtr.Zero;
			RootType = RootTypeOptions.BySpecialFolder;
			RootSpecialFolder = ShellApi.CSIDL.CSIDL_DESKTOP;
			RootPath = "";
			m_DisplayName = "";
			Title = "";
			UserToken = IntPtr.Zero;
			m_FullName = "";

			// Default flags values
			DetailsFlags = BrowseInfoFlag.BIF_BROWSEINCLUDEFILES 
				| BrowseInfoFlag.BIF_EDITBOX 
				| BrowseInfoFlag.BIF_NEWDIALOGSTYLE 
				| BrowseInfoFlag.BIF_SHAREABLE
				| BrowseInfoFlag.BIF_STATUSTEXT
				| BrowseInfoFlag.BIF_USENEWUI
				| BrowseInfoFlag.BIF_VALIDATE;

		}

		public void ShowDialog()
		{
			m_FullName = "";
			m_DisplayName = "";

			// Get shell's memory allocator, it is needed to free some memory later
			IMalloc pMalloc;
			pMalloc = ShellFunctions.GetMalloc();
		
			IntPtr pidlRoot;
			
			if (RootType == RootTypeOptions.BySpecialFolder)
			{
				ShellApi.SHGetFolderLocation(hwndOwner,(int)RootSpecialFolder,UserToken,0,out pidlRoot);
			}
			else	// m_RootType = RootTypeOptions.ByPath
			{
				uint iAttribute;
				ShellApi.SHParseDisplayName(RootPath,IntPtr.Zero,out pidlRoot,0,out iAttribute);
			}
									
			ShellApi.BROWSEINFO bi = new ShellApi.BROWSEINFO();
			
			bi.hwndOwner = hwndOwner;
			bi.pidlRoot = pidlRoot;
			bi.pszDisplayName = new String(' ',256);
			bi.lpszTitle = Title;
			bi.ulFlags = (uint)DetailsFlags; 
			bi.lParam = 0;
			bi.lpfn = new ShellApi.BrowseCallbackProc(this.myBrowseCallbackProc);
			
			// Show dialog
			IntPtr pidlSelected;
			pidlSelected = ShellLib.ShellApi.SHBrowseForFolder(ref bi);

			// Save the display name
			m_DisplayName = bi.pszDisplayName.ToString();

			IShellFolder isf = ShellFunctions.GetDesktopFolder();

			ShellApi.STRRET ptrDisplayName;
			isf.GetDisplayNameOf(pidlSelected,(uint)ShellApi.SHGNO.SHGDN_NORMAL | (uint)ShellApi.SHGNO.SHGDN_FORPARSING,out ptrDisplayName);
			
			String sDisplay;
			ShellLib.ShellApi.StrRetToBSTR(ref ptrDisplayName,pidlRoot,out sDisplay);
			m_FullName = sDisplay;

			if (pidlRoot != IntPtr.Zero)
				pMalloc.Free(pidlRoot);
			
			if (pidlSelected != IntPtr.Zero)
				pMalloc.Free(pidlSelected);
			
			Marshal.ReleaseComObject(isf);
			Marshal.ReleaseComObject(pMalloc);
		}


		///  <summary> Handle to the owner window for the dialog box.  </summary>
		public IntPtr hwndOwner;

		/// <summary> Select the root type </summary>
		public RootTypeOptions RootType;

		/// <summary> valid only if RootType is RootTypeOptions.ByPath </summary>
		public string RootPath;

		/// <summary> valid only if RootType is RootTypeOptions.BySpecialFolder </summary>
		public ShellApi.CSIDL RootSpecialFolder;

		/// <summary> Address of a buffer to receive the display name of the folder selected by the user. </summary>
		public string DisplayName
		{
			get
			{
				return m_DisplayName;
			}
		}
		private string m_DisplayName;

		/// <summary> 
		/// Address of a null-terminated string that is displayed above the tree view control in the dialog box. 
		/// </summary>
		public string Title;

		/// <summary> Token that can be used to represent a particular user. </summary>
		public IntPtr UserToken;

		/// <summary> Return the result of the dialog </summary>
		public string FullName
		{
			get
			{
				return m_FullName;
			}
		}
		private string m_FullName;

		public BrowseInfoFlag DetailsFlags;

	}

}