Hi all, I have a problem with regular expression validator. I have a file upload and I want to upload only Excel file. The problem is that after the postback, regular expression validator is shown. This is the code: 

        <asp:FileUpload ID="FileUpload1" runat="server" />
        <asp:Button ID="cmdUpload" runat="server" Text="Upload" ValidationGroup="Validators" /><br />
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="FileUpload1"
            ErrorMessage="Insert a file" ValidationGroup="Validators"></asp:RequiredFieldValidator><br />
        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="FileUpload1"
            ErrorMessage="Insert only Excel File" ValidationExpression="^(([a-zA-Z]:)|(\\{2}\w+)\$?)(\\(\w[\w].*))(.xls|.XLS|.xlsx|.XLSX)$"
            ValidationGroup="Validators"></asp:RegularExpressionValidator>

Thanks in advance!

turibbio:

The problem is that after the postback, regular expression validator is shown.

The code is working fine for me. Are you getting any errors on post back?

 no errors, are you sure that it works? I've tried the same code but it shows error. There's maybe a problem of property of control or validation group? Can you post me the whole aspx of your working code? Thanks!

turibbio:

no errors, are you sure that it works?

<asp:FileUpload ID="FileUpload1" runat="server" />
        <asp:Button ID="cmdUpload" runat="server" Text="Upload" ValidationGroup="Validators" /><br />
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="FileUpload1"
            ErrorMessage="Insert a file" ValidationGroup="Validators"></asp:RequiredFieldValidator><br />
        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="FileUpload1"
            ErrorMessage="Insert only Excel File" ValidationExpression ="[a-zA-Z\\].*(.doc|.xls|.XLS|.xlsx|.XLSX)$"
            ValidationGroup="Validators"></asp:RegularExpressionValidator>
             <asp:Button ID="Button1" runat="server" Text="Button"  />

 The <input type='file'> tag does not always pass back the file path. In particular, it is omitted when <form enctype="multipart/form-data" >

 You should confirm that the FileUpload control actually has the filepath before determining what's wrong with the validator. After all, the regularexpressionvalidator takes no action when it gets an empty string form the textbox.

PLBlum:

 The <input type='file'> tag does not always pass back the file path. In particular, it is omitted when <form enctype="multipart/form-data" >

 You should confirm that the FileUpload control actually has the filepath before determining what's wrong with the validator. After all, the regularexpressionvalidator takes no action when it gets an empty string form the textbox.

Thanks for the information Peter! Very Helpful