How to set files validation on FileUpload

In this Article we will discuss how to set validation when upload files by File upload control .

In this example we use RegularExpressionValidator control
<asp:regularexpressionvalidator id="RegularExpressionValidator1" runat="server" errormessage="Only mp3, m3u or mpeg files are allowed!" validationexpression="^(([a-zA-Z]:)(<a href=">\\{2}\w+)\$?)(\\(\w[\w</a>].*)) +(.mp3.MP3.Mp3.mP3)$" ControlToValidate="FileUpload1"><asp:regularexpressionvalidator>

Note : in this example we validate mp3 files so the user can select just mp3 files