Force user to select suggested entry from Windows Forms Autocomplete ComboBox in VB.Net

Hi kana250688,

The only way is to set the DropDownStyle to ComboBoxStyle.DropDownList.

Refer below code.

Database

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

Download Northwind Database

Code

C#

private void Form1_Load(object sender, EventArgs e)
{
    comboBox1.AutoCompleteSource = AutoCompleteSource.ListItems;
    comboBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
    comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
    string constr = @"Data Source=.\SQL2022;Initial Catalog=Northwind;UID=sa;PWD=pass@123;";
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter("SELECT CustomerId, ContactName FROM Customers", con))
        {
            //Fill the DataTable with records from Table.
            DataTable dt = new DataTable();
            sda.Fill(dt);

            //Insert the Default Item to DataTable.
            DataRow row = dt.NewRow();
            row[0] = 0;
            row[1] = "Please select";
            dt.Rows.InsertAt(row, 0);

            //Assign DataTable as DataSource.
            comboBox1.DataSource = dt;
            comboBox1.DisplayMember = "ContactName";
            comboBox1.ValueMember = "CustomerId";
        }
    }
}

private DataTable GetData()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string query = "SELECT CustomerId, ContactName 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(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
    comboBox1.AutoCompleteSource = AutoCompleteSource.ListItems
    comboBox1.AutoCompleteMode = AutoCompleteMode.Suggest
    comboBox1.DropDownStyle = ComboBoxStyle.DropDownList
    Dim constr As String = "Data Source=.\SQL2022;Initial Catalog=Northwind;UID=sa;PWD=pass@123;"

    Using con As SqlConnection = New SqlConnection(constr)
        Using sda As SqlDataAdapter = New SqlDataAdapter("SELECT CustomerId, ContactName FROM Customers", con)
            Dim dt As DataTable = New DataTable()
            sda.Fill(dt)
            Dim row As DataRow = dt.NewRow()
            row(0) = 0
            row(1) = "Please select"
            dt.Rows.InsertAt(row, 0)
            comboBox1.DataSource = dt
            comboBox1.DisplayMember = "ContactName"
            comboBox1.ValueMember = "CustomerId"
        End Using
    End Using
End Sub

Private Function GetData() As DataTable
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim query As String = "SELECT CustomerId, ContactName 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