asp. Net web page, ASP connects to the database, and uses asp:panel and asp:dropdownlist controls

A recent course used asp.net, I have no choice but to learn its code , Here's a paragraph asp.net Login code ：

Login.ascx：

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="Login.ascx.cs" Inherits="login" %>

<asp:Panel ID="Panel1" runat="server">
    <table width="214" border="0" cellpadding="0" cellspacing="0" class="text">
        <TR>
          <TD>
            <IMG height=57 src="images/denglu.jpg" width="214" border="0">
          </TD>
        </TR>
        <tr>
            <td align=center>
                <table width=203px bgcolor=white cellpadding=0 cellspacing=0 class="text1">
                    <tr>
                      <td align=right width=30%> identity ：</td>
                      <td align=left width=70%>
                          <asp:DropDownList ID="UserType" runat="server" Width="120">
                              <asp:ListItem Value=" Student "> Student </asp:ListItem>
                              <asp:ListItem Value=" Teachers' "> Teachers' </asp:ListItem>
                              <asp:ListItem Value=" Management "> Management </asp:ListItem>
                          </asp:DropDownList></td>
                    </tr>
                    <tr>
                      <td align=right> user name ：</td>
                      <td align=left>
			            <asp:TextBox ID="UserId" Runat="server" Width="120" /><font color="red" class="Normal">*</font>
			            <asp:RequiredFieldValidator id="RFVUserId" runat="server" ErrorMessage="<br> The username cannot be empty ." ControlToValidate="UserId" Display="Dynamic"></asp:RequiredFieldValidator>
                      </td>
                    </tr>
                    <tr>
                      <td align=right> password ：</td>
                      <td align=left>
			            <asp:TextBox ID="Password" Runat="server" CssClass="InputText" Width="120" TextMode="Password" /><font color="red">*</font>
			            <asp:RequiredFieldValidator id="RFVPassword" runat="server" ErrorMessage="<br> The password cannot be empty ." ControlToValidate="Password" Display="Dynamic"></asp:RequiredFieldValidator>
                      </td>
                    </tr>
                    <tr>
                      <td align=right> Verification Code ：</td>
                      <td align=left>
			            <asp:TextBox ID="Validator" Runat="server" Width="70"></asp:TextBox><font color="red">*</font>
			            <asp:Image ID="ValidateImage" runat="server" Height="25px" Width="50px" ImageAlign="AbsBottom" />
			            <asp:RequiredFieldValidator id="rfv" runat="server" ErrorMessage="<br> Verification code cannot be empty ." ControlToValidate="Validator" Display="Dynamic"></asp:RequiredFieldValidator>
                      </td>
                    </tr>
                    <tr>
                      <td colspan="2" align="center">
			            <asp:Button ID="LoginBtn" Runat="server" Text=" Sign in " CssClass="ButtonCss" Width="70px" OnClick="LoginBtn_Click"></asp:Button>
                      </td>
                    </tr>
		            <tr>
			            <td colspan="2" align="center"><asp:Label ID="Message" Runat="server" CssClass="GbText" Width="100%" ForeColor="Red"></asp:Label></td>
		            </tr>
                </table>
            </td>
        </tr>
		<tr><td>
				<IMG height=12 src="images/42.jpg" border="0">
		</td></tr>
    </table>
</asp:Panel>
<asp:Panel ID="Panel2" runat="server" Height="50px" Width="100%">
    <table width="214" border="0" class="text">
        <tr>
          <td align=left height=48 background="images/shuzhuo.jpg">
          </td>
        </tr>
        <tr>
          <td align=center>
            <table width="203" bgcolor=white border="0" cellpadding=0 cellspacing=0 class="text">
                <tr>
                  <td align=left>
                  &nbsp;&nbsp;&nbsp; Login as ：<font class=text1>
                  <%=Session["UserType"]%></font>
                  </td>
                </tr>
                <tr>
                  <td align=left>
                   &nbsp;&nbsp;&nbsp; User name ：
                  <font class=text1>
                  <%=Session["UserName"]%></font>
                  </td>
                </tr>
                <tr>
                  <td>
                  <hr />
                  </td>
                </tr>
            </table>
          </td>
        <tr><td>
				<IMG height=12 src="images/42.jpg" width=214 border=0>
		</td></tr>
    </table>
</asp:Panel>

Login.aspx.cs

public partial class login : System.Web.UI.UserControl
{
    
    private static string sValidator = "";  // Validation string 
    private readonly string sValidatorImageUrl = "ValidateImage.aspx?Validator=";

    protected void Page_Load(object sender, EventArgs e)
    {
    
        // Check whether the system is logged in , Determine which Panel
        if (Session["UserID"] != null)
        {
    
            // Already logged in , Show “ My desk ”
            this.Panel1.Visible = false;
            this.Panel2.Visible = true;
        }
        else
        {
    
            // Not logged in 
            this.Panel2.Visible = false;
            this.Panel1.Visible = true;
            
            // If the page is loaded for the first time , Create a verification code 
            if (!Page.IsPostBack)
            {
    
                // Create validation string 
                sValidator = CreateValidateString(4);
                // Set the... Of the verification code image ImageUrl attribute 
                ValidateImage.ImageUrl = sValidatorImageUrl + sValidator;
            }

            // Give a default user type .0- Student ;1- teacher ;2- Management 
            this.UserType.SelectedIndex = 2;
        }
    }

    // Create validation string 
    private string CreateValidateString(int nLen)
    {
    
        // Create a StringBuilder object 
        StringBuilder sb = new StringBuilder(nLen);
        Random rnd = new Random();
        int rndi = 1000 + rnd.Next(8999);
        sb.Append(rndi.ToString());
        return (sb.ToString());
    }

    // User presses “ Sign in ” Button to verify 
    protected void LoginBtn_Click(object sender, EventArgs e)
    {
    
        // If the page input is illegal 
        if (! Page.IsValid)return;

        // If the verification code is entered incorrectly 
        if (Validator.Text != sValidator)
        {
    
            Message.Text = " Error in captcha input , Please re-enter .";
            // Recreate the validation string 
            sValidator = CreateValidateString(4);
            // Reset the verification code picture ImageUrl attribute 
            ValidateImage.ImageUrl = sValidatorImageUrl + sValidator;
            return;
        }

        String userId = "";
        String userName = "";

        // Define the class and get the login information of the user  
        User user = new User();

        // Encode user input 
        //string sUserType = Server.HtmlEncode(UserType.SelectedItem.Value.ToString());
        string sUserType = Request.Params["Login1$UserType"].ToString();
        string sUserId = Server.HtmlEncode(UserId.Text.Trim());
        string sPassword = Server.HtmlEncode(Password.Text.Trim());

        // Get user information 
        SqlDataReader dr = user.GetUserLoginBySQL(sUserType, sUserId, sPassword);

        // Judge whether the user is legal 
        if (dr.Read())
        {
    
            userId = dr["UserID"].ToString();
            userName = dr["UserName"].ToString();
        }
        dr.Close();

        // Verify user legitimacy , And jump to the system platform 
        if ((userId != null) && (userId != ""))
        {
    
            // Write session object 
            Session["UserType"] = sUserType;
            Session["UserID"] = userId;
            Session["UserName"] = userName;

            // Write Cookies
            Response.Cookies["userInfo"]["UserType"] = sUserType;
            Response.Cookies["userInfo"]["UserID"] = userId;
            Response.Cookies["userInfo"]["UserName"] = userName;
            Response.Cookies["userInfo"].Expires = DateTime.Now.AddDays(1);

            // Jump to the system home page after login 
            //Response.Redirect("~/mainframe.aspx");
            Response.Write("<script>window.open('mainframe.aspx','_top');</script>");
        }
        else
        {
    
            // Create validation string 
            sValidator = CreateValidateString(4);
            ValidateImage.ImageUrl = sValidatorImageUrl + sValidator;
            // Display error message 
            Message.Text = " Wrong user name or password .";
        }
    }
}

Connect to database ：

using System;
using System.Data;
using System.Configuration;   //  Read  Web.config
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;    // In order to connect SQL Server database 
//using System.Data.OracleClient; // In order to connect Oracle database , You also need to add references 
using System.Data.OleDb;        // In order to connect OleDb database 

public partial class _Default : System.Web.UI.Page 
{
    
    protected void Page_Load(object sender, EventArgs e)
    {
    

    }

    protected void Button1_Click(object sender, EventArgs e)
    {
    
        string connectionString = "";

        try
        {
    
            switch (DropDownList1.Text.ToString())
            {
    
                case "SQL Server":
                    connectionString = ConfigurationManager.ConnectionStrings["SQLConnectionString"].ConnectionString;
                    SqlConnection SQLConn = new SqlConnection(connectionString);
                    SQLConn.Open();
                    Response.Write(" Link status ：" + (SQLConn.State == ConnectionState.Open ? " Link successful ." : " link failure .") + "<br>");
                    Response.Write(" Link string ：" + SQLConn.ConnectionString + "<br>");
                    Response.Write("ConnectionTimeout：" + SQLConn.ConnectionTimeout.ToString() + "<br>");
                    Response.Write("DataSource：" + SQLConn.DataSource + "<br>");
                    Response.Write("ServerVersion：" + SQLConn.ServerVersion + "<br>");
                    SQLConn.Close();
                    break;
                case "Access":
                    connectionString = ConfigurationManager.ConnectionStrings["AccessConnectionString"].ConnectionString;
                    OleDbConnection AccessConn = new OleDbConnection(connectionString);
                    AccessConn.Open();
                    Response.Write(" Link status ：" + (AccessConn.State == ConnectionState.Open ? " Link successful ." : " link failure .") + "<br>");
                    Response.Write(" Link string ：" + AccessConn.ConnectionString + "<br>");
                    Response.Write("ConnectionTimeout：" + AccessConn.ConnectionTimeout.ToString() + "<br>");
                    Response.Write("DataSource：" + AccessConn.DataSource + "<br>");
                    Response.Write("ServerVersion：" + AccessConn.ServerVersion + "<br>");
                    AccessConn.Close();
                    break;
                default :
                    Response.Write("Please select a kind of Database.<br>");
                    break;
            }
        }
        catch (Exception ex)
        {
    
            /// Display the message of connection error 
            Response.Write(ex.Message + "<br>");
        }
    }
}