Why do I get the error object reference not set to instance of an ojbect while adding an object to a list in c# wpf?

Question

I have a C# WPF application with a form in it. The form is supposed to take two values(firstName and lastName) and then use the Instructor class to add it to my listview element. On the line instList.Add(new Instructor... I am getting the error object reference not set to instance of an object. Why does this happen?

This is my mainwindow.xaml.cs:

namespace AssignmentTwoPartTwo
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public List<Instructor> instList;
        public MainWindow()
        {
            InitializeComponent();
            List<Instructor> instList = new List<Instructor> { };
            lvInstructorList.ItemsSource = instList;
        }

        private void btnCreateInstructor_Click(object sender, RoutedEventArgs e)
        {
            spCreateInstructor.Visibility = (spCreateInstructor.Visibility == Visibility.Hidden) ? Visibility.Visible : Visibility.Hidden;
        }

        private void btnInstructorSubmit_Click(object sender, RoutedEventArgs e)
        {
            instList.Add(new Instructor() { firstName = txtInstructorFirstName.Text, lastName = txtInstructorLastName.Text });
            lvInstructorList.ItemsSource = instList;
        }
    }
}

This is Instructor.cs

namespace AssignmentTwoPartTwo
{
    public class Instructor
    {
        public string firstName { set; get; }
        public string lastName { set; get; }
    }
}

Did you try debugging? At which statement does it show that error? — snit80, Sep 16 '16 at 00:08

score 0 · Answer 1 · answered Sep 16 '16 at 00:01

0

Pays to use a debugger here, you have 3 things that could cause it

instList.Add
txtInstructorFirstName.Text
txtInstructorLastName.Text

I'd say the top one is least likely.

answered Sep 16 '16 at 00:01

Keith Nicholas

43,549
15
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So how do I fix it? – ShoeLace1291 Sep 16 '16 at 00:04

score 0 · Answer 2 · answered Sep 16 '16 at 00:05

0

You are redeclaring the instList in the constructor, which shadows your instance variable. If you change your constructor to this, it should work:

public MainWindow()
{
    InitializeComponent();
    instList = new List<Instructor> { };
    lvInstructorList.ItemsSource = instList;
}

answered Sep 16 '16 at 00:05

Nico

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Good catch... buts its still a duplicate – BradleyDotNET Sep 16 '16 at 00:06
Ok... but you have to admit that the linked post is very verbose for his case ;-). – Nico Sep 16 '16 at 00:07
2

Hopefully verbose enough he won't have to ask questions like this in the future :) In fact, this case is listed under "Bad Naming Conventions" – BradleyDotNET Sep 16 '16 at 00:08

Why do I get the error object reference not set to instance of an ojbect while adding an object to a list in c# wpf?

2 Answers2