Exception in foreach loop of adding struct to List

Question

Hi guys I have suc­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­h code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        struct Proxy
        {
            public static List<string> proxyList;
            public static string type;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Title = "Choose file with proxy";
            openFileDialog1.InitialDirectory = System.Environment.CurrentDirectory;
            openFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            if (checkBox1.Checked)
                Proxy.type = "socks5";
            else
                Proxy.type = "http";
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                foreach (string prox in File.ReadAllLines(openFileDialog1.FileName))
                {
                    if (prox.Contains(":"))
                    {
                        string[] proxy = prox.Split(':');
                        Proxy.proxyList.Add(prox);
                    }
                }
                MessageBox.Show(Proxy.proxyList.Count.ToString());
            }
        }

    }
}

But when I load txt file:

62.109.28.37:8085
193.0.147.23:8085
193.0.147.90:8085
193.0.147.61:8085
193.0.147.47:8085
193.0.147.93:8085

I receive an exception: on line Proxy.proxyList.Add(prox); Object reference not set to an instance of an object.

Why?=\

Answer 1

Because proxyList is null. Change

public static List<string> proxyList;

to

public static List<string> proxyList = new List<string>();

Answer 2

You need to construct the list too, before you use it, e.g., before your foreach loop:

Proxy.proxyList = new List<string>();

Or you could do this in the struct definition itself:

    struct Proxy
    {
        public static List<string> proxyList = new List<string>();
        public static string type;
    }