How To Use a Common Dialog File Open Dialog with Win32 API

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Article ID: 161286 - View products that this article applies to.
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This article provides a code sample and demonstrates how to use the File Open dialog box in the Comdlg32.dll. Making use of Comdlg32.OCX is a good reuse of resources under Windows, because Windows always has its dependent file, Comdlg32.dll, loaded. It provides an easy-to-use interface, but can be a performance hit. If you use the OCX control, you have to load the module into memory and also distribute a 90K OCX control to users of your software. To improve performance, you should minimize the use of controls in your applications. Instead, you can use the Win32 API calls directly.

If you use the API calls, you may lose some of the functionality that Comdlg32.OCX offers, such as the Help button. If you require the Help button, you will need to use the Comdlg32.OCX control.


Step-by-Step Example

  1. Start Visual Basic 5.0 and select Standard EXE. If Visual Basic 5.0 is already running, click New Project on the File menu and select Standard EXE. Form1 is created by default.
  2. Place a CommandButton on Form1.
  3. Add the following code to the Form1 code window:
          Option Explicit
           Private Declare Function GetOpenFileName Lib "comdlg32.dll" Alias _
             "GetOpenFileNameA" (pOpenfilename As OPENFILENAME) As Long
           Private Type OPENFILENAME
             lStructSize As Long
             hwndOwner As Long
             hInstance As Long
             lpstrFilter As String
             lpstrCustomFilter As String
             nMaxCustFilter As Long
             nFilterIndex As Long
             lpstrFile As String
             nMaxFile As Long
             lpstrFileTitle As String
             nMaxFileTitle As Long
             lpstrInitialDir As String
             lpstrTitle As String
             flags As Long
             nFileOffset As Integer
             nFileExtension As Integer
             lpstrDefExt As String
             lCustData As Long
             lpfnHook As Long
             lpTemplateName As String
           End Type
           Private Sub Command1_Click()
             Dim OpenFile As OPENFILENAME
             Dim lReturn As Long
             Dim sFilter As String
             OpenFile.lStructSize = Len(OpenFile)
             OpenFile.hwndOwner = Form1.hWnd
             OpenFile.hInstance = App.hInstance
             sFilter = "Batch Files (*.bat)" & Chr(0) & "*.BAT" & Chr(0)
             OpenFile.lpstrFilter = sFilter
             OpenFile.nFilterIndex = 1
             OpenFile.lpstrFile = String(257, 0)
             OpenFile.nMaxFile = Len(OpenFile.lpstrFile) - 1
             OpenFile.lpstrFileTitle = OpenFile.lpstrFile
             OpenFile.nMaxFileTitle = OpenFile.nMaxFile
             OpenFile.lpstrInitialDir = "C:\"
             OpenFile.lpstrTitle = "Use the Comdlg API not the OCX"
             OpenFile.flags = 0
             lReturn = GetOpenFileName(OpenFile)
             If lReturn = 0 Then
                MsgBox "The User pressed the Cancel Button"
                MsgBox "The user Chose " & Trim(OpenFile.lpstrFile)
             End If
           End Sub
  4. Press the F5 key to run the project, and click the CommandButton. You should see the File Open dialog box appear with the options set.


The Win32 SDK documents other calls to the Comdlg32.dll such as ChooseColor, ChooseFont, and GetSaveFileName.

For more information, please see the following article in the Microsoft Knowledge Base:
106682 : Default Extension Ignores File Type in VB Common Dialog


Article ID: 161286 - Last Review: July 13, 2004 - Revision: 2.2
  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
  • Microsoft Visual Basic 4.0 Standard Edition
  • Microsoft Visual Basic 4.0 Professional Edition
  • Microsoft Visual Basic 4.0 32-Bit Enterprise Edition
kbhowto KB161286

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