Display datagridview rows based on similar ID

using System;
using System.Data;
using System.IO;
using System.Windows.Forms;

namespace DataGridViewFilter_Sb9m
{
    public partial class MainForm : Form
    {
        private DataTable fullDataTable; //Store all of the loaded data...
        private DataView filteredDataView; //View to display data your user filtered by...
        private int currentRowIndex = 0; //Index of the currently displayed row...

        public MainForm()
        {
            InitializeComponent();
        }

        private void MainForm_Load(object sender, EventArgs e)
        {
            //Load data from file and create your DataTable...
            string filename = theDialog.FileName;
            using (StreamReader reader = File.OpenText(filename))
            {
                string[] columnnames = reader.ReadLine().Split('|');
                fullDataTable = new DataTable();
                foreach (string c in columnnames)
                {
                    fullDataTable.Columns.Add(c);
                }

                string newline;
                while ((newline = reader.ReadLine()) != null)
                {
                    DataRow dr = fullDataTable.NewRow();
                    string[] values = newline.Split('|');
                    for (int i = 0; i < values.Length; i++)
                    {
                        dr[i] = values[i];
                    }
                    fullDataTable.Rows.Add(dr);
                }
            }

            //Set up the initial DataView with all data...
            filteredDataView = new DataView(fullDataTable);

            //Show data based on the initial index...
            ShowDataAtIndex(currentRowIndex);
        }

        private void ShowDataAtIndex(int index)
        {
            if (index >= 0 && index < filteredDataView.Count)
            {
                DataRowView rowView = filteredDataView[index];
                //Assuming your ID column is named ID as per your supplied code...
                string selectedID = rowView["ID"].ToString();
                //Display the selected ID's data in your DataGridView...
                dataGridView.DataSource = filteredDataView.ToTable();

                //Update label to show the filtered current ID...
                currentIDLabel.Text = "Current ID: " + selectedID;
            }
        }
        //I added this button to load the next rows...
        private void NextButton_Click(object sender, EventArgs e)
        {
            currentRowIndex++;
            if (currentRowIndex >= filteredDataView.Count)
            {
                //If it reached the end, loop back to the beginning...
                currentRowIndex = 0;
            }
            ShowDataAtIndex(currentRowIndex);
        }

        private void FilterButton_Click(object sender, EventArgs e)
        {
            //Filter your data based on the selected ID...
            string selectedID = filterTextBox.Text;
            filteredDataView.RowFilter = $"ID = '{selectedID}'";

            //Reset the current index and display data...
            currentRowIndex = 0;
            ShowDataAtIndex(currentRowIndex);
        }
    }
}