キューバナーが必要なようです。これらはComboBoxコントロールでも機能します。
Private Const CBM_FIRST As Long = &H1700&
Private Const CB_SETCUEBANNER As Long = CBM_FIRST + 3
Private Const ECM_FIRST As Long = &H1500&
Private Const EM_SETCUEBANNER As Long = ECM_FIRST + 1
Private Declare Function SendMessage Lib "user32" Alias "SendMessageW" ( _
ByVal hWnd As Long, _
ByVal wMsg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long
Private Sub SetCueBannerTXT(ByVal TextBox As TextBox, ByVal CueText As String)
SendMessage TextBox.hWnd, EM_SETCUEBANNER, 0, StrPtr(CueText)
End Sub
Private Sub SetCueBannerCBO(ByVal ComboBox As ComboBox, ByVal CueText As String)
SendMessage ComboBox.hWnd, CB_SETCUEBANNER, 0, StrPtr(CueText)
End Sub
注このAPIを使用するには、Comclt32.dllバージョン6.0を指定するマニフェストを提供する必要があります。