How To Use a Common Dialog File Open Dialog with Win32 API (161286)

SUMMARY

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.

MORE INFORMATION

Step-by-Step Example

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.
Place a CommandButton on Form1.

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"
         Else
            MsgBox "The user Chose " & Trim(OpenFile.lpstrFile)
         End If
       End Sub

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.

REFERENCES

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

For more information, please see the following articles in the Microsoft Knowledge Base:

106682 : Default Extension Ignores File Type in VB Common Dialog

137194 : GetOpenFileName nMaxFile Interpreted Incorrectly