Updated textbox value can't be reached by code

Question

In this code I read the patient infos from database with patientId parameter passed with URL. Then I fill the 5 textboxes with this values at Page_Load. But at Update_Click the code can't reach the updated textbox values, it reads only initial values of the textboxes. I saw it at debugging. No problems at database level. When I remove the Page_Load code and leave the textboxes empty initially, the code from Update_Click can reach the user input and update the values. What is the problem?

using MySql.Data.MySqlClient;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Configuration;

public partial class admin_Testadmin : System.Web.UI.Page
{
    Patient patient = new Patient();

    protected void Page_Load(object sender, EventArgs e)
    {
      String cs = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;

      using (MySqlConnection cn = new MySqlConnection(cs))
      {
        MySqlCommand command = new MySqlCommand(StoredProcedures.select_patient, cn);
        command.CommandType = CommandType.StoredProcedure;

        int pid = int.Parse(Request.QueryString["patientId"]);
        command.Parameters.AddWithValue("pid", pid);
        command.Parameters["pid"].Direction = ParameterDirection.Input;
        cn.Open();

        MySqlDataReader reader = command.ExecuteReader();

        while (reader.Read())
        {
          txtName.Text = patient.Name = (String)reader[0];
          txtSurname.Text = patient.Surname = (String)reader[1];
          txtFathersname.Text = patient.Fathersname = (String)reader[2];
          txtStatus.Text = patient.Status = (String)reader[3];
          txtSuccessDescription.Text = patient.SuccessDescription = (String)reader[4];
          patient.Id = (int)reader[5];
        }
        reader.Close();
        cn.Close();
      }
    }

    protected void Update_Click(object sender, EventArgs e)
    {    
      String cs = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;

      using (MySqlConnection cn = new MySqlConnection(cs))
      {
        MySqlCommand command = new MySqlCommand(StoredProcedures.update_patient, cn);
        command.CommandType = CommandType.StoredProcedure;
        patient.Name = txtName.Text.Trim();
        patient.Surname = txtSurname.Text.Trim();
        patient.Fathersname = txtFathersname.Text.Trim();
        patient.Status = txtStatus.Text.Trim();
        patient.SuccessDescription = txtSuccessDescription.Text;
        patient.Id = int.Parse(Request.QueryString["patientId"]);


        command.Parameters.Add("pname", MySqlDbType.VarChar).Value = patient.Name;
        command.Parameters.Add("psurname", MySqlDbType.VarChar).Value = patient.Surname;
        command.Parameters.Add("pfathersname", MySqlDbType.VarChar).Value = patient.Fathersname;
        command.Parameters.Add("pstatus", MySqlDbType.VarChar).Value = patient.Status;
        command.Parameters.Add("psuccessdescription", MySqlDbType.Text).Value = patient.SuccessDescription;

        command.Parameters.AddWithValue("pid", patient.Id);
        command.Parameters["pid"].Direction = ParameterDirection.Input;

        cn.Open();
        if (command.ExecuteNonQuery() > 0)
        {
          ResultLabel.Text = "";
          ResultLabel.Text = "Update success";
        }
        cn.Close();
      }
    }
}

Answer 1

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
        return;

    // Rest of your code here
}

In the case of a postback, you do not want to overwrite what the user typed.

Here are some docs about the ASP.NET page life cycle.