AutoComplete TextBox Validation in Windows Forms using C# and VB.Net

Hi kana250688,

Please refer the below sample.

Database

I have made use of the following table Customers with the schema as follows.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

Form Design

I have added a TextBox and a Label control to the Form.

The TextBox has been assigned with a TextChanged event handler.

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#

private void Form1_Load(object sender, EventArgs e)
{
    AutoCompleteStringCollection acsCustomers = new AutoCompleteStringCollection();
    foreach (DataRow dr in this.GetData().Rows)
    {
        acsCustomers.Add(dr["Name"].ToString());
    }
    txtCustomers.AutoCompleteMode = AutoCompleteMode.Suggest;
    txtCustomers.AutoCompleteSource = AutoCompleteSource.CustomSource;
    txtCustomers.AutoCompleteCustomSource = acsCustomers;
}

private void txtCustomers_TextChanged(object sender, EventArgs e)
{
    lblError.Hide();
    DataRow[] rows = this.GetData().Select("Name='" + txtCustomers.Text.Trim() + "'");
    if (rows.Length == 0)
    {
        lblError.Show();
    }
}

private DataTable GetData()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string query = "SELECT Name FROM Customers";
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand(query, con))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    return dt;
                }
            }
        }
    }
}

VB.Net

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim acsCustomers As AutoCompleteStringCollection = New AutoCompleteStringCollection()
    For Each dr As DataRow In Me.GetData().Rows
        acsCustomers.Add(dr("Name").ToString())
    Next
    txtCustomers.AutoCompleteMode = AutoCompleteMode.Suggest
    txtCustomers.AutoCompleteSource = AutoCompleteSource.CustomSource
    txtCustomers.AutoCompleteCustomSource = acsCustomers
End Sub

Private Sub txtCustomers_TextChanged(ByVal sender As Object, ByVal e As EventArgs) Handles txtCustomers.TextChanged
    lblError.Hide()
    Dim rows As DataRow() = Me.GetData().Select("Name='" & txtCustomers.Text.Trim() & "'")
    If rows.Length = 0 Then
        lblError.Show()
    End If
End Sub

Private Function GetData() As DataTable
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim query As String = "SELECT Name FROM Customers"
    Using con As SqlConnection = New SqlConnection(conString)
        Using cmd As SqlCommand = New SqlCommand(query, con)
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    Return dt
                End Using
            End Using
        End Using
    End Using
End Function

Screenshot