Rewrite DirectoryInfo using IShellFolder

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Introduction

DirectoryInfo is a class to represent a folder in disk, it's suitable to list file system entries, but it cannot be used to represent a special folder (e.g. virtual folder that doesn't exist in the disk). You may have to use IShellFolder to enumerate these directories. DirectoryInfoEx is written to support these folders.

The project is a rewrite based on Steven Roebert's C# File Browser's code and article. His code does even more than my project, his article emphasizes on how to take advantage of the shell once you have a complete implementation (e.g. context menu, shell drag and drop, preview handler, etc), but lacks documentation about how to create one. I rewrite part of his code (the core part) to learn how it works, and this article explain how to do the basic file operations using IShellFolder interface, in C#.

Because of my lack of knowledge, and the nature of DirectoryInfo / FileInfo, the new class is a lot simpler than CShellItem.

Index

• Obtaining PIDL
• IShellFolder interface
• IStorage interface
• IStream interface
• My DirectoryInfoEx implementation
• Demo

Obtaining PIDL

Folders and Files in shell namespace can be located by PIDL (ITEMIDLIST), just like folder path (or DisplayName), there are Relative PIDL and Full PIDL, just like relative path (abc.txt) and full path (c:\abc.txt).

To obtain PIDL from a string path, you can use Desktop's IShellFolder."http://msdn.microsoft.com/en-us/library/bb775090%28VS.85%29.aspx" target="_blank" rel="nofollow">ParseDisplayName() (see below):

ShellAPI.SFGAO pdwAttributes = 0;
DesktopShellFolder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero,
     path, ref pchEaten, out pidlPtr, ref pdwAttributes);
PIDL pidl = new PIDL(pidlPtr, false); 

For special directories (e.g. virtual ones like DRIVES, or special file system directories like PROFILE), CSIDL enum has a list of them, you can use SHGetSpecialFolderLocation() to obtain it's PIDL.

int RetVal = ShellAPI.SHGetSpecialFolderLocation(IntPtr.Zero, csidl, out ptrAddr);
if (ptrAddr != IntPtr.Zero)
{
  pidl = new PIDL(ptrAddr, false);
  return pidl;
}

Obtaining IShellFolder Interface

Desktop is the root of all shell namespace folder, you can use SHGetDesktopFolder() to obtain the IShellFolder interface for Desktop.

IntPtr ptrShellFolder = IntPtr.Zero;

if (ShellAPI.SHGetDesktopFolder(out ptrShellFolder) == ShellAPI.S_OK)
  iShellFolder = (IShellFolder)Marshal.GetTypedObjectForIUnknown(ptrShellFolder,
     typeof(IShellFolder)); 

As for other directories (including non-file directory, e.g. MyComputer), you can use BindToObject().

if (Parent.ShellFolder.BindToObject(pidl.Ptr, IntPtr.Zero,
   ref ShellAPI.IID_IShellFolder, out ptrShellFolder) == ShellAPI.S_OK)

  iShellFolder = (IShellFolder)Marshal.GetTypedObjectForIUnknown(ptrShellFolder,
     typeof(IShellFolder)); 

IShellFolder Interface

This contains methods to manage the folder, e.g.:

• Obtain a list of subitems (sub-folders / sub-files), e.g.

  static ShellAPI.SHCONTF folderflag = ShellAPI.SHCONTF.FOLDERS |
   ShellAPI.SHCONTF.INCLUDEHIDDEN;
   /* Specify to include folders only */
  
  if (iShellFolder.EnumObjects(IntPtr.Zero, folderflag, out ptrEnum)
      == ShellAPI.S_OK) //return the pointer of IEnumIDList
  {
     IEnumIDList IEnum = (IEnumIDList)Marshal.GetTypedObjectForIUnknown(ptrEnum,
       typeof(IEnumIDList));
     IntPtr pidlSubItem;
     int celtFetched;
  
     while (IEnum.Next(1, out pidlSubItem, out celtFetched) == ShellAPI.S_OK
       && celtFetched == 1)
         dirList.Add(new PIDL(pidlSubItem, false));
  /*  Add PIDL of each subdirectory to dirList, noted that in normal case you
   *  should release pidlSubItem but Steven Roebert's PIDL class is a IDisposable
   *  class which will dispose it for you.
   *  Also noted that the pidl is relative instead of full.
   *  Use GetDisplayNameOf() (see below) to get it's name. */
  
     if (IEnum != null) //Release resource
     {
        Marshal.ReleaseComObject(IEnum);
        Marshal.Release(ptrEnum);
      }
    } 

• Convert PIDL back to readable path using GetDisplayNameOf() :

  IntPtr ptrStr = Marshal.AllocCoTaskMem(ShellAPI.MAX_PATH * 2 + 4);
  Marshal.WriteInt32(ptrStr, 0, 0);
  StringBuilder buf = new StringBuilder(ShellAPI.MAX_PATH);
  
  try
  {
    /*  uflags is a SHGNO enum that allow you to get different folder names,
     *  e.g. "My Documents"(SHGNO.NORMAL) folder is named as
     *       "Documents"(SHGNO.FORPARSING) in file system.
     *  StrRetToBuf() convert STRRET structure to
     *  buffer usable by StringBuilder */
  if (iShellFolder.GetDisplayNameOf(pidl, uFlags, ptrStr) == ShellAPI.S_OK)
      ShellAPI.StrRetToBuf(ptrStr, pidl, buf, ShellAPI.MAX_PATH);
  }
  finally
  {
    if (ptrStr != IntPtr.Zero)
      Marshal.FreeCoTaskMem(ptrStr);
    ptrStr = IntPtr.Zero;
  }
  Console.WriteLine(buf.ToString()); 

• Retrieve IShellFolder / IStorage interface for a subfolder :

  Using SHBindToParent() :

  IntPtr pidlLast = IntPtr.Zero;
  retVal = ShellAPI.SHBindToParent(dir.PIDLRel.Ptr, ShellAPI.IID_IStorage,
    out storagePtr, ref pidlLast); 

  Or BindToStorage():

  retVal = dir.Parent.ShellFolder.BindToStorage(
                      dir.PIDLRel.Ptr, IntPtr.Zero, ref ShellAPI.IID_IStorage,
                      out storagePtr);
  /* Beside IID_IStorage interface, there is IID_IStream and
     IID_IPropertySetStorage as well. */
  
  if ((retVal == ShellAPI.S_OK))
  {
    IStorage storage = (IStorage)Marshal.GetTypedObjectForIUnknown(storagePtr,
    typeof(IStorage));
    /* Your work here, free the pointer and interface when done. */
  } 

IStorage Interface

This contains methods for creation or to manage items / subitems in the folder, e.g.

• Rename, move or copy files, using pidl as parameter. e.g.

  SrcStorage.MoveElementTo(SourceFileName, DestStorage,
     DestFilename, ShellAPI.STGMOVE.MOVE) != ShellAPI.S_OK) 

• Delete files:

  ParentStorage.DestroyElement(name); 

• Read / Write files contents:

  /* FileStreamEx class is a customized IDisposable Stream class,
   * which uses IStream interface of a file. */
  FileStreamEx stream = new FileStreamEx(path, mode, access);
  StreamReader sr = new StreamReader(stream);
  Console.WriteLine(sr.ReadToEnd()); 

IStream Interface

This allows you to read / write data to stream objects.

• To obtain the IStream interface, use OpenStream() (Read/Write) or CreateStream() (Create New):

  if (parentStorage.OpenStream(filename, IntPtr.Zero, grfmode, 0,
    out streamPtr) == ShellAPI.S_OK)
      stream = (IStream)Marshal.GetTypedObjectForIUnknown(streamPtr,
        typeof(IStream)); 

• IStream contains methods like seek(), read(), write().
• If the stream object is released, it is consider closed.

All interface objects should be released when done.

My DirectoryInfoEx Implementation

The implementation is simpler than CShellItem, however, as FileSystemInfoEx's PIDL is exposed (via PIDLRel and PIDL property), you can implement custom operation (e.g. Extract Icon, Context Menu) externally. IShellFolder and IStorage (generate on demand) are also exposed in DirectoryInfoEx, they are automatically destroyed when disposed, do not free them yourself.

Both DirectoryInfoEx and FileInfoEx are inherited from FileSystemInfoEx, they are used as enumeration (listing) subitems, DirectoryInfoEx contains GetFiles() and GetDirectories() method for this purpose. To modify a file, use FileEx class for managing files (DirectoryEx is not implemented yet, use System.IO.Directory at this time), and FileStreamEx class for read/write files.

DirectoryInfoEx (and FileInfoEx)'s constructor accept a Path or PIDL. A number of special directories are defined in DirectoryInfoEx, including DesktopDirectory, MyComputerDirectory, CurrentUserDirectory, SharedDirectory and NetworkDirectory. For other special directories, you can obtain it's PIDL by calling DirectoryInfoEx.CSIDLtoPIDL().

And a Demo

This demo is a simple WPF application that lists the subdirectories below Desktop. The Icons are obtained using SHGetFileInfo(), which takes a full PIDL parameter.

Issues

• DirectoryEx static class is not implemented.
• Haven't figured out how to get IShellFolder directly, current implementation looks up from Desktop directory (e.g. C:\ = Desktop, Computer, C:\ = 3 times), which is slower.

References

• C# File Browser (Steven Roebert)
• VB Explorer Tree (Jim Parsells)
• Over Reaction To: A Simple WPF Explorer Tree (Karl on WPF)
• MSDN

History

• 08-22-09 Initial version
• 08-23-09 Version 2, demo updated
• 11-01-09 Version 4, demo updated