vb.net时间差

您好！数据库表tests，数据：像：toffel      2016-02-27
在listbox1中选中“toffel”，在textbox1中显示“2016-02-27”，在textbox2中显示：还有“61”天

Dim mysql As String = "select tdate from tests where tname ='" & ListBox1.SelectedItem.ToString & "'"

        Dim mycmd As New SqlClient.SqlCommand(mysql, myconn)

        myconn.Open()

        Try

            TextBox1.Text = mycmd.ExecuteScalar()

        Catch ex As Exception

            MsgBox(ex.Message)

        End Try

        myconn.Close()

        Dim dt As Date

        dt = CDate(Format(CInt(TextBox1.Text), "0000-00-00"))

        Dim b As Date = System.DateTime.Today

        Dim c As Long = DateDiff("d", dt, b)

        TextBox2.Text = c