View AutoComplete list on ASP.Net Ajax AutoCompleteExtender TextBox focus using C# and VB.Net

Hi nauna,

You need to set the MinimumPrefixLength="0" to display list on click of TextBox.

Refer below example.

Database

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

Download Northwind Database

HTML

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
</asp:ScriptManager>
<asp:TextBox ID="txtContactsSearch" runat="server"></asp:TextBox>
<cc1:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server" ServiceMethod="SearchCustomers"
    MinimumPrefixLength="0" CompletionInterval="100" EnableCaching="false" CompletionSetCount="10"
    TargetControlID="txtContactsSearch" FirstRowSelected="false">
</cc1:AutoCompleteExtender>

Namespaces

C#

using System.Data.SqlClient;
using System.Configuration;
using System.Web.Services;

VB.Net

Imports System.Data.SqlClient
Imports System.Configuration
Imports System.Web.Services

Code

C#

[WebMethod]
public static List<string> SearchCustomers(string prefixText, int count)
{
    using (SqlConnection conn = new SqlConnection())
    {
        conn.ConnectionString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = "select ContactName from Customers where ContactName like @SearchText + '%'";
            cmd.Parameters.AddWithValue("@SearchText", prefixText);
            cmd.Connection = conn;
            conn.Open();
            List<string> customers = new List<string>();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                {
                    customers.Add(sdr["ContactName"].ToString());
                }
            }
            conn.Close();

            return customers;
        }
    }
}

VB.Net

<WebMethod()>
Public Shared Function SearchCustomers(ByVal prefixText As String, ByVal count As Integer) As List(Of String)
    Using conn As SqlConnection = New SqlConnection()
        conn.ConnectionString = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using cmd As SqlCommand = New SqlCommand()
            cmd.CommandText = "select ContactName from Customers where ContactName like @SearchText + '%'"
            cmd.Parameters.AddWithValue("@SearchText", prefixText)
            cmd.Connection = conn
            conn.Open()
            Dim customers As List(Of String) = New List(Of String)()
            Using sdr As SqlDataReader = cmd.ExecuteReader()
                While sdr.Read()
                    customers.Add(sdr("ContactName").ToString())
                End While
            End Using
            conn.Close()

            Return customers
        End Using
    End Using
End Function

Screenshot