ช่วยแนะนำ code เช็คค่าซ้ำใน combo box ด้วยครับ (ผมมี code ของผมมาให้ดูด้วย)

Imports System.Data.OleDb
Public Class Form1
    Dim objConnection As OleDbConnection
    Dim objCmd As OleDbCommand
    Dim strConnection As String
    Dim adapter As New OleDbDataAdapter
    Dim ds As New DataSet
    Dim dt As New DataTable

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        strConnection = "Provider=Microsoft.ACE.OLEDB.12.0;" & _
                        "Data Source=D:\PC_CNC.accdb"

        ' Create and open the connection object
        objConnection = New OleDbConnection(strConnection)
        objConnection.Open()

        ' Create the Command and set its properties
        objCmd = New OleDbCommand()
        objCmd.Connection = objConnection
        objCmd.CommandText = "querypositive" ' ชื่อ procedure
        'objCmd.Parameters.Add(New OleDbParameter("@param", "xxx")) 'กรณีที่มี parameter (รับตัวแปร)
        objCmd.CommandType = CommandType.StoredProcedure

        adapter.SelectCommand = objCmd
        adapter.Fill(ds)
        dt = ds.Tables(0)
        'If (dt.Rows.Count > 0) Then
        'For index = 0 To dt.Rows.Count - 1
        'Console.WriteLine(dt.Rows(index)(0))
        'Next
        dgv1.DataSource = dt
        'End If
        'Console.ReadLine()

        If dgv1.RowCount > 1 Then
            Dim TotalPrice As Integer = 0
            For index As Integer = 0 To dgv1.RowCount - 1
                TotalPrice += Convert.ToInt32(dgv1.Rows(index).Cells(8).Value)
            Next
            txt1.Text = Format$(TotalPrice, "###,###,###,###")
        End If

        cb1.DataSource = ds.Tables(0)
        cb1.DisplayMember = "Vender"
        ListBox1.DataSource = ds.Tables(0)
        ListBox1.ValueMember = "ToolNumberID"
        ListBox2.DataSource = ds.Tables(0)
        ListBox2.ValueMember = "Totall"
        ListBox3.DataSource = ds.Tables(0)
        ListBox3.ValueMember = "Price"
        ListBox4.DataSource = ds.Tables(0)
        ListBox4.ValueMember = "Total Price"