[kslawy]

كود :

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


        Me.ComboBox1.Items.Add("None")
        Me.ComboBox1.Items.Add("A")
        Me.ComboBox1.Items.Add("B")
        Me.ComboBox1.Items.Add("C")
        '***********************************
        Me.ComboBox2.Items.Add("None")
        Me.ComboBox2.Items.Add("A")
        Me.ComboBox2.Items.Add("B")
        Me.ComboBox2.Items.Add("C")


    End Sub


    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        If Me.ComboBox1.Text = Me.ComboBox2.Text Then
            'None يتم اختيار القيمة الأولى وهي
            Me.ComboBox2.SelectedIndex = 0
        End If
    End Sub


    Private Sub ComboBox2_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox2.SelectedIndexChanged
        If Me.ComboBox2.Text = Me.ComboBox1.Text Then
            'None يتم اختيار القيمة الأولى وهي
            Me.ComboBox1.SelectedIndex = 0
        End If
    End Sub