How to convert string to date in vb.net

try this code

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

        If (TextBox1.Text.Length = 2 Or TextBox1.Text.Length = 5) Then
            TextBox1.Text = TextBox1.Text + "/"
            TextBox1.SelectionStart = TextBox1.Text.Length
        End If

        If (TextBox1.Text.Length = 8) Then

            Dim date_str As String = TextBox1.Text
            Dim split_date As String() = date_str.Split("/")
            Dim thisDate As DateTime = New DateTime(Convert.ToInt32("20" + split_date(2)), _
                                                      Convert.ToInt32(split_date(1)), _
                                                      Convert.ToInt32(split_date(0)))
            TextBox1.Text = thisDate.ToString("d/MM/yyyy")
        End If

    End Sub

try this : Microsoft.VisualBasic.Format(txtSample, "MM/dd/yyyy")
much better if you use a masktextbox and add this code . . .
and code should be like this : Microsoft.VisualBasic.Format(msktextbox, "MM/dd/yyyy")

i have an DatetimePicker Control and Problame is

if Listview.item(i).subitem(3).text ="" then

Expirydate.value = Format(Now.Date,"MM/yyyy")

else

Expirydate.value = "28/" & Listview.item(i).subitem(3).text


Above code if givint Problame if Error converting String to date in vb.net 2012