VB 读取列表文件名

Private Sub Command1_Click()
Dim d As String, s As String

If Dir(App.Path & "\down", vbDirectory) = "" Then
Label1.Caption = "img目录不存在无法执行下一步"
Else
d = Dir(App.Path & "\down\*.*")
Open App.Path & "\dianying.txt" For Append As #1
Do Until d = ""
s = LCase(Right(d, 4))
If s = ".mp4" Then Print #1, d
d = Dir
Loop
Close #1
Label1.Caption = "引擎装载完毕"
End If
End Sub