NullReference When Attempting to Store in Variable's String

Question

I have two projects in my solution: HomeworkCalendar (VB.net Windows Forms Application) and HWLib (C# .dll Class Library). In the CurrentUser class in the library I have a variable defines as HWLib.User currentUser. This comes from the User class in HWLib:

namespace HWLib
{
    public class User
    {
        /// <summary>
        /// The Name of the User
        /// </summary>
        public String name = null;
        /// <summary>
        /// The Age of the User
        /// </summary>
        public int age = 0;
        /// <summary>
        /// The School Type of the User
        /// </summary>
        public String school = null;
        /// <summary>
        /// The Amount of Classes the User
        /// </summary>
        public int classesCount = 0;
        /// <summary>
        /// The String Array that holds all the classes
        /// </summary>
        public string[] classes;
    }
 }

Here is as it is in the CurrentUser class

public class CurrentUser
{
    /// <summary>
    /// The current User using the program
    /// </summary>
    public static HWLib.User currentUser;
}

So I attempted to store the user information into this variable, but this is where I get a NullReferenceException

Try
    If intClasses <= 11 Then
        CurrentUser.currentUser.name = txtName.Text
        CurrentUser.currentUser.classesCount = intClasses
        CurrentUser.currentUser.school = cboSchool.SelectedItem
        CurrentUser.currentUser.age = Convert.ToInt32(cboAge.SelectedItem)
    End if
Catch exx As NullReferenceException
   'It does catch! This is the issue! Why does it catch here and how do I fix it?
    File.Delete(Base.filePath)
    MsgBox(exx.ToString())
End Try

Which line throws the exception? Use the debugger!! Put a breakpoint on that line and then run the program. When it reaches that breakpoint, hover your mouse over the various variables. It will tell you which one is null. — Chris Dunaway, May 20 '14 at 14:22
there are literally 42,000 exact duplicates of this on SO; 10 or so right over there =====> under RELATED — Ňɏssa Pøngjǣrdenlarp, May 20 '14 at 14:25

score 2 · Accepted Answer · answered May 20 '14 at 14:21

Well, to get it to run you'll need to initialize currentUser:

public class CurrentUser
{
    /// <summary>
    /// The current User using the program
    /// </summary>
    public static HWLib.User currentUser = new HWLib.User() ;
}

but:

Why do you have a non-static class with just a static property? Just make CurrentUser static
It is a better practice to use properties (with getters/setters) instead of fields. THat allows you to add logic to the get/set without breaking client code.

Thank you! It was a silly mistake on my part. I really should've known that this was oging to be needed. — user2678408, Nov 03 '14 at 13:31

NullReference When Attempting to Store in Variable's String

1 Answers1