你好，
你可以使用RequiredFieldValidator控件，例如：
<asp:FileUpload ID="FileUpload1" runat="server" />
<br />
<asp:RequiredFieldValidator ErrorMessage="Required" ControlToValidate="FileUpload1"
runat="server" Display="Dynamic" ForeColor="Red" />
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" ValidationExpression="([a-zA-Z0-9\s_\\.\-:])+(.doc|.docx|.pdf)$"
ControlToValidate="FileUpload1" runat="server" ForeColor="Red" ErrorMessage="Please select a valid Word or PDF File file."
Display="Dynamic" />
<br />
<asp:Button Text="Submit" runat="server" />
另外你也可以使用JQuery添加验证。
<script type ="text/javascript">
var validFilesTypes=["bmp","gif","png","jpg","jpeg","doc","xls"];
function ValidateFile()
{
var file = document.getElementById("<%=FileUpload1.ClientID%>");
var label = document.getElementById("<%=Label1.ClientID%>");
var path = file.value;
var ext=path.substring(path.lastIndexOf(".")+1,path.length).toLowerCase();
var isValidFile = false;
for (var i=0; i<validFilesTypes.length; i++)
{
if (ext==validFilesTypes[i])
{
isValidFile=true;
break;
}
}
if (!isValidFile)
{
label.style.color="red";
label.innerHTML="Invalid File. Please upload a File with" +
" extension:\n\n"+validFilesTypes.join(", ");
}
return isValidFile;
}
</script>
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="btnUpload" runat="server" Text="Upload"
OnClientClick = "return ValidateFile()" OnClick="btnUpload_Click" />
<br />
<asp:Label ID="Label1" runat="server" Text="" />
更多详细信息，请参考下面的链接：
http://www.aspsnippets.com/Articles/ASPNet-FileUpload-File-Extension-Validation.aspx
http://www.aspsnippets.com/Articles/Validate-FileUpload-Control-using-Regular-Expression-and-RegularExpression-Validator-in-ASPNet.aspx
