System.IO.Path.GetExtension returns null in ASP.NET

Question

I have a fileupload in my page so the user can browse the computer and select the file. After selecting the file when I want to get the name of file using this code:

string ext = System.IO.Path.GetExtension(FileUpload1.PostedFile.FileName);

It returns null and I got this error :

Object reference not set to an instance of an object.

After debugging I found that my file is posted null and it doesn't send. Why? After adding a little code I got this error :

<asp:UpdatePanel runat="server" ID="UpdatePanel1" UpdateMode="Always">
        <ContentTemplate>
<div class="wrapper-box">
                                <div class="topbox">
                                    عکس خبر
                                </div>
                                 <asp:FileUpload ID="FileUpload1" runat="server" CssClass="text-input-two" />
                            </div>


        </ContentTemplate>
    </asp:UpdatePanel>

How can it return null AND throw an exception? Please be more specific: which line of code throws the exception? — helb, Apr 23 '14 at 11:16
System.IO.Path.GetExtension(FileUpload1.PostedFile.FileName); this line Throws an exception — user3527150, Apr 23 '14 at 11:19
Almost all cases of `NullReferenceException` are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Apr 23 '14 at 11:33
Try to check if FileUpload1.PostedFile is null, sometimes the asp:FileUpload component don't work with update panel — bdn02, Apr 23 '14 at 15:18

Neel · Answer 1 · 2014-04-23T11:31:26.110

According to MSDN GetExtension will only return null if you pass in a FileName that's null.

The extension of the specified path (including the period "."), or Nothing[Null], or String.Empty. If path is Nothing[Null], GetExtension returns Nothing[Null]. If path does not have extension information, GetExtension returns String.Empty.

So check if (file != null && file.FileName != null) first before proceeding furthure.

score 1 · Answer 2 · answered Apr 23 '14 at 11:27

1

Get extension method returns a extension of file. check following code sample

string s = System.IO.Path.GetExtension("file1.aspx");

you can use FileUpload1.fileName instead of fileupload1.postedfile.filename

hope it helps

answered Apr 23 '14 at 11:27

koolprasad2003

299
3
23

score 0 · Answer 3 · answered Nov 23 '18 at 05:31

Try adding this postback trigger between and

</ContentTemplate>
  <Triggers>
     <asp:PostBackTrigger ControlID="Button1" />
  </Triggers>
</asp:UpdatePanel>

And add enctype="multipart/form-data" to your form

<form id="form1" runat="server" enctype="multipart/form-data">

score 0 · Answer 4 · answered Nov 23 '18 at 05:40

0

Use

string ext = System.IO.Path.GetExtension("FileName.ext");

Instead of

string ext = System.IO.Path.GetExtension(FileUpload1.PostedFile.FileName);

answered Nov 23 '18 at 05:40

Brijesh Kumar Tripathi

1,762
15
25

System.IO.Path.GetExtension returns null in ASP.NET

4 Answers4