Add ListItem to DropDownList from TextBox using C# and VB.Net in ASP.Net

Hi nauna,

Check this example. Now please take its reference and correct your code. Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

<asp:DropDownList runat="server" ID="ddlCountries" AppendDataBoundItems="true" Width="150px">
    <asp:ListItem Text="Select" Value="0" Selected="True" />
</asp:DropDownList>
<asp:TextBox runat="server" ID="txtCountry" AutoPostBack="true" OnTextChanged="CountryChange" Width="150px" />

Namespaces

C#

using System.Configuration;
using System.Data;
using System.Data.SqlClient;

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BindCountries();
    }
}

protected void CountryChange(object sender, EventArgs e)
{
    ddlCountries.ClearSelection();
    ddlCountries.Items.Add(new ListItem { Text = txtCountry.Text.Trim(), Value = txtCountry.Text.Trim(), Selected = true });
}

private void BindCountries()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string query = "SELECT DISTINCT Country FROM Employees";
    SqlCommand cmd = new SqlCommand(query);
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            cmd.Connection = con;
            sda.SelectCommand = cmd;
            using (DataTable dt = new DataTable())
            {
                sda.Fill(dt);
                ddlCountries.DataSource = dt;
                ddlCountries.DataTextField = "Country";
                ddlCountries.DataValueField = "Country";
                ddlCountries.DataBind();
            }
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        BindCountries()
    End If
End Sub

Protected Sub CountryChange(ByVal sender As Object, ByVal e As EventArgs)
    ddlCountries.ClearSelection()
    ddlCountries.Items.Add(New ListItem With {.Text = txtCountry.Text.Trim(), .Value = txtCountry.Text.Trim(), .Selected = True})
End Sub

Private Sub BindCountries()
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim query As String = "SELECT DISTINCT Country FROM Employees"
    Dim cmd As SqlCommand = New SqlCommand(query)
    Using con As SqlConnection = New SqlConnection(conString)
        Using sda As SqlDataAdapter = New SqlDataAdapter()
            cmd.Connection = con
            sda.SelectCommand = cmd
            Using dt As DataTable = New DataTable()
                sda.Fill(dt)
                ddlCountries.DataSource = dt
                ddlCountries.DataTextField = "Country"
                ddlCountries.DataValueField = "Country"
                ddlCountries.DataBind()
            End Using
        End Using
    End Using
End Sub

Screenshot