How to Quickly List the Contents of a Directory

• Standard and Professional Editions of Microsoft Visual Basic for Windows, version 3.0

SUMMARY

Although Visual Basic has both built-in functions (Dir$ and Dir) and a built-in control (File list box) for listing the files in a directory, using a standard list box and the Windows API SendMessage function lists files in a directory much more quickly.

NOTE: Replacing the File list box or Dir command using the technique described in this article will only improve performance perceptibly if the File list box or Dir command is used heavily in the application.

MORE INFORMATION

This technique uses the LB_DIR message for list boxes to add a list of filenames to a list box. To do this, call the Windows API SendMessage function. The SendMessage function requires the following parameters to list the files:

   SendMessage (hWnd%, LB_DIR, wParam%, lParam)

   hWnd%    is the handle of the list box.
   wParam%  is an integer that specifies the permissible file
            attributes.
   lParam   is a long pointer to a string containing the full path and
            file name to add to the list. This can include wildcards.

Value             Meaning

DDL_ARCHIVE       File has been archived.
DDL_DIRECTORY     File must be a directory name.
DDL_EXCLUSIVE     Exclusive flag. If the exclusive flag is set, only
                  files of the specified type are listed. Otherwise,
                  files of the specified type are listed in addition to
                  files that do not match the specified type.
DDL_HIDDEN        File must be hidden.
DDL_READONLY      File must be read only.
DDL_READWRITE     File can be read from or written to.
DDL_SYSTEM        File must be a system file.

Step-by-Step Example

1. Start Visual Basic; or, choose New Project from the File menu (ALT+F, N) if Visual Basic is already running. Form1 is created by default.

2. Add a list box (List1) to Form1.

3. Add a new code module to the project by choosing New Module from the File menu.

4. Add the following code to the new code module:

      ' Enter the Declare statement on one single line:
      Declare Function SendMessage Lib "user" (ByVal hwnd As Integer,
                                               ByVal wMsg As Integer,
                                               ByVal wParam As Integer,
                                               lParam As Any) As Long
   
   

5. Declare the following constants in the General Declaration section of the code module

         Global Const WM_USER = &H400
         Global Const LB_DIR = WM_USER + 14
         Global Const DDL_ARCHIVE = &H0020
         Global Const DDL_DIRECTORY = &H0010
         Global Const DDL_EXCLUSIVE = &H8000
         Global Const DDL_HIDDEN = &H0002
         Global Const DDL_READONLY = &H0001
         Global Const DDL_READWRITE = &H0000
         Global Const DDL_SYSTEM = &H0004
   

6. To fill the list box with all of the files, which may or may not be hidden, in the C:\WINDOWS directory, place the following code in the Form_Load event of Form1:

         Sub Form_Load ()
            List1.Clear
            s$ = "C:\WINDOWS\*.*"
            i% = SendMessage(List1.hWnd, LB_DIR, DDL_HIDDEN, ByVal s$)
         End Sub
   
   

7. Press the F5 key to run the application.