API関数GetOpenFileNameを、VBAから呼び出して使うプログラム例です。標準モジュールにコピー して使ってみてください。


Public 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

Public Declare Function GetOpenFileName Lib "comdlg32.dll" Alias "GetOpenFileNameA" _
    (pOpenfilename As OPENFILENAME) As Long
    
Public Const OFN_FILEMUSTEXIST = &H1000

Public Const MAX_PATH = 260

　以上をDeclarationsに書いてください。以下はユーザー定義関数です。
以下のTst_APIShowをVB Editorから実行するとプログラムの動作を見ることが出来ます。

Public Sub Tst_APIShow()
'
' WindowsAPI関数GetOpenFileNameを呼び出してオープンするファイル名（フルパス名）
'を得るテストプログラム
'
  Dim full_path_name As String, title_name As String
  Dim opn_file_name   As OPENFILENAME
  Dim output_string As String
'
'  opn_file_nameの初期化全てのメンバをナルに
'
  Call Initialize_Struct(opn_file_name)
'
'full_path_nameとtitle_nameの文字数を設定する
'
  full_path_name = String(260, " ")
  title_name = String(64, " ")
   
   If Set_StructMem(opn_file_name, full_path_name, title_name) <> False Then
     MsgBox full_path_name
   End If
  
End Sub

Public Function Set_StructMem(opn_name_strct As OPENFILENAME, file_full_title As String, file_title As String) As Long
'
'注意　ナル文字(\0)等の取得方法がC言語と違っている
'lpstrFilterでフィルタ文字列に空白を入れてはならない
'
    Dim flag_val As Long
  
    opn_name_strct.lStructSize = 76&
    opn_name_strct.hwndOwner = 0&
    opn_name_strct.lpstrFilter = "全ての図" & Chr("\0") & "*.bmp;*.jpg;*.gif;*.ico;*.wmf" & Chr("\0") & Chr("\0")
    opn_name_strct.lpstrCustomFilter = vbNullString
    
    opn_name_strct.lpstrFile = file_full_title
    opn_name_strct.nMaxFile = MAX_PATH
    opn_name_strct.lpstrFileTitle = file_title
    opn_name_strct.nMaxFileTitle = 64&
    opn_name_strct.lpstrTitle = "表示する図・写真・絵を選んでください"
    opn_name_strct.flags = OFN_FILEMUSTEXIST
    
    Set_StructMem = GetOpenFileName(opn_name_strct)
    
    file_full_title = opn_name_strct.lpstrFile
    
End Function

Public Sub Initialize_Struct(opn_name_strct As OPENFILENAME)
'
' OPENFILENAME構造体を初期化する。文字列の初期化に注意
'
With opn_name_strct

    .lStructSize = 0&
    .hwndOwner = 0&
    .hInstance = 0&
    .lpstrFilter = vbNullString
    .lpstrCustomFilter = vbNullString
    .nMaxCustFilter = 0&
    .nFilterIndex = 0&
    .lpstrFile = vbNullString
    .nMaxFile = 0&
    .lpstrFileTitle = vbNullString
    .nMaxFileTitle = 0&
    .lpstrInitialDir = vbNullString
    .lpstrTitle = vbNullString
    .flags = 0&
    .nFileOffset = 0
    .nFileExtension = 0
    .lpstrDefExt = vbNullString
    .lCustData = 0&
    .lpfnHook = 0&
    .lpTemplateName = vbNullString

End With

End Sub
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