System.NullReferenceException: while writing to XML file

Question

I am creating a signup page and the file used to store the user details via regiration form is XML file. When I am writing the entries using the code below the system is throwing an exception of NullReferenceException.

 protected void register_Click(object sender, EventArgs e)
{
    try
    {
        //var path = Path.Combine(Request.PhysicalApplicationPath, "App_Data\\PageData.xml");
        XDocument doc = XDocument.Load(Server.MapPath("~/App_Data/userlogs.xml"));
        XElement user = new XElement("user",
            new XElement("fname", fname.Text.ToString()),
            new XElement("lname", lname.Text.ToString()),
            new XElement("dob", dob.Text.ToString()),
            new XElement("uid", uid.Text.ToString()),
            new XElement("pwd", pwd.Text.ToString()),
            new XElement("email", email.Text.ToString()),
            new XElement("lastlog", System.DateTime.Now.ToString())
            );
        doc.Root.Element("users").Add(user);
        doc.Save("userlog.xml");
    }
    catch (Exception exe)
    {
        error.Visible = true;
        error.Text = exe.ToString();
    }
}

My userslog.xml File format:-

<users>
    <user>
        <fname>abc</fname>
        <lname>xyz</lname>
        <dob>MM/DD/YYYY</dob>
        <uid>username</uid>
        <pwd>***</pwd>
        <email>[email protected]</email>
        <lastlog>DATE:TIME</lastlog>
    </user>
</users>

By this code i want to create new tag

<users>
    <user>
        <fname>abc</fname>
        <lname>xyz</lname>
        <dob>MM/DD/YYYY</dob>
        <uid>username</uid>
        <pwd>***</pwd>
        <email>[email protected]</email>
        <lastlog>DATE:TIME</lastlog>
    </user>
    <user>
        <fname>bcd</fname>
        <lname>lmo</lname>
        <dob>MM/DD/YYYY</dob>
        <uid>username1</uid>
        <pwd>***</pwd>
        <email>[email protected]</email>
        <lastlog>DATE:TIME</lastlog>
    </user>
</users>

So it want my code to make my file run in the following desired manner.

I am getting the following error on debugging

There shouldn't be any attempt to figure out. You just do it. When your program throws the error, the IDE will clearly indicate which line it is (execute your program in debug mode). — Jeroen Vannevel
– Jeroen Vannevel, Commented Nov 15, 2013 at 2:56

Sudhakar Tillapudi · Accepted Answer · 2013-11-15 03:24:36Z

1

from the code given there can be one possibility for getting NullReferenceException

1.Please check wether your xml file is available or not in following path:

~/App_Data/userlogs.xml

--> your file should be placed in RootFolder of Project/App_Data/

before proceeding further you can Check wether file exists or not by:

System.IO.File.Exists(filepath)
{
//true so file exists
//contine
}

answered Nov 15, 2013 at 3:24

Sudhakar Tillapudi

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5 Comments

o12d10 Over a year ago

My file is in the RootFolder of the project and it does exist. I checked the same by deleting the file the system. It is throwing File not found exception.

Sudhakar Tillapudi Over a year ago

sorry i did not get you, your files is in the RootFolder?

o12d10 Over a year ago

yes . my userslog.xml lies in App_Data directory. and it is correctly linked in the program and normally accessed.

o12d10 Over a year ago

no it is not. .i have added a snapshot in my question of the errors that i am getting. can you check the pic and tell me.

Sudhakar Tillapudi Over a year ago

try adding like this => doc.Root.Add(user);

User2012384 · Accepted Answer · 2013-11-15 04:03:13Z

0

Try debugging the program.

Remove the try catch part, so that the program will flow the exception

Add a breakpoint to see how the program runs

Try these:

does the file App_Data/userlogs.xml exists?
is the "doc" object null?

Post more code if possible

edited Nov 15, 2013 at 4:03

answered Nov 15, 2013 at 3:06

User2012384

4,92717 gold badges74 silver badges107 bronze badges

5 Comments

o12d10 Over a year ago

the file exists. . . . The NullReferenceException is coming on -doc.Root.Element("users").Add(User);

User2012384 Over a year ago

Then did you check whether the "doc" is null or the "User" is null?

User2012384 Over a year ago

or the "doc.Root.Element("user") is null?

o12d10 Over a year ago

my root node is <users>. and user is not null

User2012384 Over a year ago

Try typing "doc.Root.Element("users")" in the immediate window and see what's the output

o12d10 · Accepted Answer · 2013-11-15 04:38:47Z

This is the final working code: thanks to @sudhakar

protected void register_Click(object sender, EventArgs e)
{
        //var path = Path.Combine(Request.PhysicalApplicationPath, "App_Data\\PageData.xml");
    File.Exists("~/App_Data/userlogs.xml");
    {
        XDocument doc = XDocument.Load(Server.MapPath("~/App_Data/userlogs.xml"));
        XElement user = new XElement("user",
            new XElement("fname", fname.Text.ToString()),
            new XElement("lname", lname.Text.ToString()),
            new XElement("dob", dob.Text.ToString()),
            new XElement("uid", uid.Text.ToString()),
            new XElement("pwd", pwd.Text.ToString()),
            new XElement("email", email.Text.ToString()),
            new XElement("lastlog", System.DateTime.Now.ToString())
            );
        doc.Root.Add(user);
        doc.Save(Server.MapPath("~/App_Data/userlogs.xml"));
    }
}

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