ASP.Net - Error accessing static method of unstatic class
<p>I'm developing a website as a school project using Microsoft Visual Web Developer and C# based-ASP.Net.</p>

<p>I have implemented a simple class to represent a User as it is formed in a db. The class
Has members that represent the columns in the db, and a couple of static methods to create an instance from a DataTable result. The following code is used (MyDbase is some help class we were given):</p>

<pre class="lang-or-tag-here prettyprint-override"><code>//User.cs, placed in A
using System;

public class User
{
    private int id;
    private String email;
    private String firstName;
    private String lastName;
    private String username;
    private String passwd;
    private String birthDate;
    private bool isMale;
    private String phone;
    private String avatarUrl;
    private bool isAdmin;

    ... //Accessors and mutators

    public User( int _id, String _email, String _firstName, String _lastName, String _username, String _passwd,
                String _birthDate, bool _isMale, String _phone, String _avatarUrl, bool _isAdmin )
    {
        this.id = _id;
        this.email = _email;
        this.firstName = _firstName;
        this.lastName = _lastName;
        this.username = _username;
        this.passwd = _passwd;
        this.birthDate = _birthDate;
        this.isMale = _isMale;
        this.phone = _phone;
        this.avatarUrl = _avatarUrl;
        this.isAdmin = _isAdmin;
    }

    public static User getUserForSqlResult(System.Data.DataTable result)
    {
        User newUser = null;
        if (result.Rows.Count == 1)
        {
            newUser = new User((int)result.Rows[0]["id"], (String)result.Rows[0]["email"], 
                                (String)result.Rows[0]["firstName"], (String)result.Rows[0]["lastName"], (String)result.Rows[0]["username"],
                                (String)result.Rows[0]["passwd"], (String)result.Rows[0]["birthDate"], (bool)result.Rows[0]["isMale"],
                                (String)result.Rows[0]["phone"], (String)result.Rows[0]["avatarUrl"], (bool)result.Rows[0]["isAdmin"]);
        }

        return newUser;
    }

    public static User getUserById(int id)
    {
        System.Data.DataTable dt = MyDbase.SelectFromTable("select * from tUsers where id=" + id, "db.mdb");
        return getUserForSqlResult(dt);
    }

    public void saveUserChanges()
    {
        MyDbase.ChangeTable("UPDATE tUsers SET email='" + this.email + "', firstName='" + this.firstName + "', lastName='" + this.lastName +
                            "', passwd='" + this.passwd + "', birthDate='" + this.birthDate + "', phone='" + this.phone + "', avatarUrl='" +
                            this.avatarUrl + "' WHERE id=" + this.id , "db.mdb");
    }
}
</code></pre>

<p>I tried to run the following sample code just to make sure the select&amp;update functions are working (Default.aspx):
</p>

<pre><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {

        User user = User.getUserById(3);
        user.setEmail("different@email.com");
        user.saveUserChanges();
    }
}
</code></pre>

<p>However, I get the following error:</p>

<blockquote>
  <p>Error 1 'System.Security.Principal.IPrincipal' does not contain a
  definition for 'getUserById' and no extension method 'getUserById'
  accepting a first argument of type
  'System.Security.Principal.IPrincipal' could be found (are you missing
  a using directive or an assembly reference?)</p>
</blockquote>

<p>Any ideas why this might happen?
Tnx!</p>
