c# fileupload 如何設定檔案型別

//取得檔案的副檔名,並轉換成小寫

& & & & & & & & & & & string fileExtension = System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();

& & & & & & & & & & & //限定只能上傳jpg和gif圖片

& & & & & & & & & & & string[] allowExtension = { ".jpg", ".gif", ".txt", ".xls" };