Visual Basic Callbacks
SHBrowseForFolder: Restrict Browse Selection to a CD/DVD via Callback
Posted:   Wednesday March 31, 2004
Updated:   Monday December 26, 2011
Applies to:   VB5, VB6
Developed with:   VB6, Windows XP
OS restrictions:   None
Author:   Randy Birch - VBnet


SHBrowseForFolder: Browse Folders Dialog Overview
SHBrowseForFolder: Browse for Folders Dialog
SHBrowseForFolder: Browse for Folders Callback Overview
SHBrowseForFolder: Browse for Folders New UI Features
SHBrowseForFolder: Pre-selecting Folders using a Browse Callback

CSIDL / Folders:
Shell and Common Controls Versions, CSIDL Constants
SHGetFolderPath: Retrieve Windows Shell Folders (Best Practice)

Windows / Shell Versions:
GetFileVersionInfo: Handy Routines for Identifying Shell32 Versions
GetVersionEx: Windows Version Info (Wrapper Routines)

VB5 / VB6. Note that the NEW UI enhancements require Shell version 5 or 6.

Using a SHBrowseForFolder callback along with GetDriveType(), it is possible to limit the user's selection to a valid CD-ROM, CD-RW, or DVD reader or writer.  The code presented below disables the OK button if GetDriveType for the selected file system object is not the DRIVE_CDROM type. This also restricts the selection to the actual drive letter; selecting a subfolder on the drive also disables the OK button.

The illustration shows the affect selecting different drives have on the OK button. For demo purposes the display name of the selected and valid drive is also shown in the second text box. This will be the volume label of the drive if the CD/DVD is empty, or the volume label of the inserted CD/DVD if present.

 BAS Module Code
Add the following code to a BAS module:

Option Explicit
' Copyright 1996-2011 VBnet/Randy Birch, All Rights Reserved.
' Some pages may also contain other copyrights by the author.
' Distribution: You can freely use this code in your own
'               applications, but you may not reproduce 
'               or publish this code on any web site,
'               online service, or distribute as source 
'               on any media without express permission.
Public Const NOERROR As Long = 0
Public Const CSIDL_DRIVES As Long = &H11
Public Const DRIVE_CDROM As Long = 5
Public Const MAX_PATH As Long = 260

Public Declare Function GetDriveType Lib "kernel32" _
   Alias "GetDriveTypeA" _
  (ByVal nDrive As String) As Long

Private Declare Function SendMessage Lib "user32" _
   Alias "SendMessageA" _
   (ByVal hwnd As Long, _
   ByVal wMsg As Long, _
   ByVal wParam As Long, _
   lParam As Any) As Long
'messages from browser
Private Const BFFM_INITIALIZED As Long = 1
Private Const BFFM_SELCHANGED As Long = 2
Private Const BFFM_VALIDATEFAILED As Long = 3

'messages to browser
Private Const WM_USER = &H400
Private Const BFFM_SETSTATUSTEXT  As Long = (WM_USER + 100)
Private Const BFFM_ENABLEOK As Long = (WM_USER + 101)
Private Const BFFM_SETSELECTION As Long = (WM_USER + 102)

Public Declare Function SHGetPathFromIDList Lib "shell32" _
     Alias "SHGetPathFromIDListA" _
     (ByVal pidl As Long, ByVal pszPath As String) As Long
Private Declare Function lstrlenW Lib "kernel32" _
  (ByVal lpString As Long) As Long

Public Function BrowseDriveCallbackProc(ByVal hwnd As Long, _
                                        ByVal uMsg As Long, _
                                        ByVal lParam As Long, _
                                        ByVal lpData As Long) As Long
   Dim spath As String
   Dim bFlag As Long

   Select Case uMsg
        'disable selection of the root item
        'on startup
         Call SendMessage(hwnd, BFFM_ENABLEOK, 0, ByVal 0&)
        'although not used in creating the screen shot, 
        'above, we can change the caption of the dialog
        'from the usual Browse For Folders, which is now
        'misleading, to something more applicable
         Call SetWindowText(hwnd, "Browse for CD/DVD Drive") 
        'a buffer for SHGetPathFromIDList
         spath = Space$(MAX_PATH)
        'lparam contains the PIDL of the
        'selected item, which can be resolved
        'to a file system path with SHGetPathFromIDList
         If SHGetPathFromIDList(lParam, spath) Then

           'if drive type is CD set True othewise False
            bFlag = (GetDriveType(spath) = DRIVE_CDROM)
            Call SendMessage(hwnd, BFFM_ENABLEOK, 0, ByVal bFlag)
         End If
      Case Else

   End Select

End Function

Public Function TrimNull(startstr As String) As String

   TrimNull = Left$(startstr, lstrlenW(StrPtr(startstr)))
End Function

Public Function FARPROC(pfn As Long) As Long
  'A dummy procedure that receives and returns
  'the value of the AddressOf operator.
  'This workaround is needed as you can't 
  'assign AddressOf directly to a member of a 
  'user-defined type, but you can assign it 
  'to another long and use that instead! 
  FARPROC = pfn

End Function
 Form Code

To create this project, add to a form one command button (Command1), two text boxes (Text1, Text2) and a checkbox (Check1).  Add the following code to the form:

Option Explicit
'For finding a folder to start document searching
Private Const BIF_RETURNONLYFSDIRS As Long = &H1

'For starting the Find Computer

'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.
Private Const BIF_STATUSTEXT As Long = &H4


'Add an edit box to the dialog: SHELL 4.71 or later only!
Private Const BIF_EDITBOX As Long = &H10

'insist on valid result (or CANCEL)
Private Const BIF_VALIDATE As Long = &H20

'Use the new dialog layout with the ability 
'to resize: SHELL 5.0 or later only!
Private Const BIF_NEWDIALOGSTYLE As Long = &H40

'Allow URLs to be displayed or entered 
'(Requires BIF_USENEWUI): SHELL 5.0 or later only!
Private Const BIF_BROWSEINCLUDEURLS As Long = &H80

'Add a UA hint to the dialog, in place of the
'edit box. May not be combined with BIF_EDITBOX: SHELL 6.0 or later only!
Private Const BIF_UAHINT As Long = &H100

'Do not add the "New Folder" button to the dialog.
'Only applicable with BIF_NEWDIALOGSTYLE: SHELL 6.0 or later only!
Private Const BIF_NONEWFOLDERBUTTON As Long = &H200

'Browsing for Computers
Private Const BIF_BROWSEFORCOMPUTER As Long = &H1000

'Browsing for Printers
Private Const BIF_BROWSEFORPRINTER As Long = &H2000

'Browsing for Everything
Private Const BIF_BROWSEINCLUDEFILES As Long = &H4000

'sharable resources on remote systems displayed  
'(remote shares, requires BIF_USENEWUI): SHELL 5.0 or later only!
Private Const BIF_SHAREABLE As Long = &H8000&

Private Type BROWSEINFO    'bi
   hOwner As Long
   pidlRoot As Long
   pszDisplayName As String   'return display name of item selected
   lpszTitle As String        'text to go in the banner over the tree
   ulFlags As Long            'flags that control the return stuff
   lpfn As Long
   lParam As Long             'extra info passed back in callbacks
   iImage As Long             'output var: where to return the Image index
End Type

Private Declare Function SHBrowseForFolder Lib "shell32.dll" _
   Alias "SHBrowseForFolderA" _
  (lpBrowseInfo As BROWSEINFO) As Long

Private Declare Function SHGetSpecialFolderLocation _
   Lib "shell32.dll" _
  (ByVal hwndOwner As Long, _
   ByVal nFolder As Long, _
   pidl As Long) As Long
Private Declare Sub CoTaskMemFree Lib "ole32.dll" (ByVal pv As Long)

Private Sub Form_Load()
   Command1.Caption = "Select only CD ROMs"
   Check1.Caption = "Use New UI"
   Text1.Text = ""
   Text2.Text = ""
End Sub

Private Sub Command1_Click()

   Dim bNewDialog As Boolean
   bNewDialog = Check1.Value = vbChecked
   Text1.Text = GetBrowseCdrom(Me.hwnd, bNewDialog)

End Sub

Private Function GetBrowseCdrom(hwndOwner As Long, _
                                bNewDialog As Boolean) As String

  'return only a valid local CD or DVD
   Dim pidl As Long
   Dim spath As String
  'obtain the pidl to the special folder 'drives'
   If SHGetSpecialFolderLocation(hwndOwner, _
                                 CSIDL_DRIVES, _
                                 pidl) = NOERROR Then
     'fill in the required members, limiting the
     'Browse to the local file system by specifying
     'the returned pidl as pidlRoot
      With bi
         .hOwner = hwndOwner
         .pidlRoot = pidl
         .pszDisplayName = Space$(MAX_PATH) 'return value-param name is misleading!
         .lpszTitle = "Select any CD-ROM or DVD (reader or writer)" 'message, not dialog title!
         .lpfn = FARPROC(AddressOf BrowseDriveCallbackProc)
         .ulFlags = BIF_RETURNONLYFSDIRS Or _
        'if the shell version is 5.0 or greater 
        'the new UI style can be applied. If the 
        'shell version is 6.0 or later, using 
        'BIF_NEWDIALOGSTYLE will display a New Folder 
        'button by default. Since we're returning CD/DVDs, 
        'we add the 'no new folder' flag if the new UI 
        'is chosen.
         If bNewDialog Then .ulFlags = .ulFlags Or _
                                        BIF_NEWDIALOGSTYLE Or _
      End With
     'show the browse dialog and return
     'the PIDL for the selected folder
      pidl = SHBrowseForFolder(bi)
      If pidl <> 0 Then
        'got a PIDL .. is it valid?
         spath = Space$(MAX_PATH)
         If SHGetPathFromIDList(ByVal pidl, ByVal spath) Then
           'valid, so return the drive
            GetBrowseCdrom = TrimNull(spath)
           'but first, just for this demo info,
           'set Text2 to show the displayname
           'returned from the call
            Text2.Text = bi.pszDisplayName

         End If 'If SHGetPathFromIDList
         Call CoTaskMemFree(pidl)
      End If 'If pidl
   End If 'If SHGetSpecialFolderLocation

End Function


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Copyright 1996-2011 VBnet and Randy Birch. All Rights Reserved.
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