Code Snippet
Public Class Form1
Private Sub Form_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
Dim dt As New DataTable()
dt.Columns.Add("aa")
dt.Columns.Add("bb")
For i As Integer = 0 To 19
dt.Rows.Add(i.ToString("00"), "bb" + i.ToString("00"))
Next
Me.ComboBox1.DisplayMember = "bb"
Me.ComboBox1.ValueMember = "aa"
Me.ComboBox1.DataSource = dt
Me.ComboBox1.SelectedIndex = -1
AddHandler Me.ComboBox1.SelectedIndexChanged, AddressOf comboBox1_SelectedIndexChanged
Me.ComboBox2.DisplayMember = "bb"
Me.ComboBox2.ValueMember = "aa"
Me.ComboBox2.DataSource = dt.Copy()
Me.ComboBox2.SelectedIndex = -1
AddHandler Me.ComboBox2.SelectedIndexChanged, AddressOf comboBox2_SelectedIndexChanged
End Sub
Private Sub comboBox2_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
If Me.ComboBox2.SelectedIndex <> -1 Then
Me.ComboBox1.SelectedIndex = -1
End If
End Sub
Private Sub comboBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
If Me.ComboBox1.SelectedIndex <> -1 Then
Me.ComboBox2.SelectedIndex = -1
End If
End Sub
End Class