Filter ASP.Net DropDownList based on TextBox using C# and VB.Net

Hi SUJAYS,

I have modified your code. Refer below sample 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:TextBox runat="server" ID="TextBox1" AutoPostBack="true" OnTextChanged="TextBox1_TextChanged" />
<asp:DropDownList runat="server" ID="ddlDescription" >
</asp:DropDownList>

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)
    {
        string strQuery = "SELECT c.Description FROM Products p INNER JOIN Categories c ON p.CategoryID = c.CategoryID";
        PopulateDropDownList(ddlDescription, "Description", "Description", strQuery);
    }
}

protected void TextBox1_TextChanged(object sender, EventArgs e)
{
    string strQuery = "SELECT c.Description FROM Products p INNER JOIN Categories c ON p.CategoryID = c.CategoryID";
    if (!string.IsNullOrEmpty(TextBox1.Text))
    {
        strQuery += " WHERE SupplierID = '" + TextBox1.Text + "'";
    }
    PopulateDropDownList(ddlDescription, "Description", "Description", strQuery);
}

private void PopulateDropDownList(DropDownList ddl, string dataTextField, string dataValueField, string query)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query, con))
        {
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                con.Open();
                DataSet ds = new DataSet();
                da.Fill(ds);
                ddl.DataTextField = dataTextField;
                ddl.DataValueField = dataValueField;
                ddl.DataSource = ds;
                ddl.DataBind();
                ddl.Items.Insert(0, new System.Web.UI.WebControls.ListItem("Please Select", "0"));
            }
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        Dim strQuery As String = "SELECT c.Description FROM Products p INNER JOIN Categories c ON p.CategoryID = c.CategoryID"
        PopulateDropDownList(ddlDescription, "Description", "Description", strQuery)
    End If
End Sub

Protected Sub TextBox1_TextChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim strQuery As String = "SELECT c.Description FROM Products p INNER JOIN Categories c ON p.CategoryID = c.CategoryID"

    If Not String.IsNullOrEmpty(TextBox1.Text) Then
        strQuery += " WHERE SupplierID = '" & TextBox1.Text & "'"
    End If

    PopulateDropDownList(ddlDescription, "Description", "Description", strQuery)
End Sub

Private Sub PopulateDropDownList(ByVal ddl As DropDownList, ByVal dataTextField As String, ByVal dataValueField As String, ByVal query As String)
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand(query, con)
            Using da As SqlDataAdapter = New SqlDataAdapter(cmd)
                con.Open()
                Dim ds As DataSet = New DataSet()
                da.Fill(ds)
                ddl.DataTextField = dataTextField
                ddl.DataValueField = dataValueField
                ddl.DataSource = ds
                ddl.DataBind()
                ddl.Items.Insert(0, New System.Web.UI.WebControls.ListItem("Please Select", "0"))
            End Using
        End Using
    End Using
End Sub

Screenshot