Can't call a function from another function?

Question

C++ / C#

Does not call XArF() in private void button1_Click(object sender, EventArgs e)
Error CS0103 The name 'XArF' does not exist in the current context.
P.S. don't worry, i'm learning...

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

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            XArF();
        }

        public RichTextBox getRichTextBox1()
        {
            return richTextBox1;
        }

    }

    public class Main : Form1
    {
        public double[] xAr;

        public void XArF()
        {
            int n = getRichTextBox1().Lines.Length;
            int k = 0;

            for (int i = 0; i < n; i++)
            {
                xAr[k] = Convert.ToInt32(getRichTextBox1().Lines[i]);
                k++;
            }
        }
    }
}

Answer 1

This method is defined in the descendant. And, of course, the base class does not have access to it.