NOTE: Для »» `Gallery` аналогично.

Office VBA_29

Sub CallbackDropDownOnAction(control As IRibbonControl, _
                             selectedId As String, _
                             selectedIndex As Integer)
    Select Case control.ID
        Case "myDropDown"
            MsgBox "У вас " & DLookup("txtName", _
                   "tblPictures", "txtPicName = '" & _
                   Format(selectedIndex, "00") & "'") & _
                   " выбрано!", vbInformation, _
                   "Это заголовок!"
    End Select
End Sub

Office XML_28

<dropDown 
 id="myDropDown" 
 label="My Dropdown:" 
 imageMso="PictureEffectsGlowGallery"
 getItemCount="CallbackDDGetItemCount"
 getItemID="CallbackDDGetItemID"
 getSelectedItemID="CallbackDDGetSelectedItemID"
 onAction="CallbackDropDownOnAction" 
 sizeString= "WWWWWWWWWWWWW">
</dropDown>