Hello people. Im learning Visual Basic 2010 on my programming class and we reached the part of file handling. Here i tried to make a simple program that can create a text file with the content of what i type on the textbox, basically i create the file if it doesn't exist, and if it already exists i append the content to it. Once the file is saved i can read it using the "Open" button. Unfortunataly, whenever i try to create the file, the compiler gives me an error saying that it cannot modify a closed file, although i've followed up the execution instruction by instruction and i can't find the error. Can some of you help me?...

Code:
Imports System.IO
Public Class Form1
    Dim body As String

    Private Sub bt_open_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_open.Click
        Dim sample As New FileStream(Application.StartupPath & tb_filename.Text, FileMode.Open, FileAccess.Read)
        Dim reader As New StreamReader(sample)
        body = reader.ReadLine
        Do While body IsNot Nothing
            tb_text.Text = tb_text.Text + body
            body = reader.ReadLine
        Loop
        sample.Close()
        reader.Close()
    End Sub

    Private Sub bt_save_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_save.Click
        If File.Exists(tb_filename.Text) Then
            Dim sample As New FileStream(Application.StartupPath & tb_filename.Text, FileMode.Append, FileAccess.Write, FileShare.ReadWrite)
            Dim writer As New StreamWriter(sample)
            body = tb_text.Text
            writer.Write(body)
            sample.Close()
            writer.Close()
        Else
            Dim sample As New FileStream(Application.StartupPath & tb_filename.Text, FileMode.CreateNew, FileAccess.Write, FileShare.ReadWrite)
            Dim writer As New StreamWriter(sample)
            body = tb_text.Text
            writer.Write(body)
            sample.Close()
            writer.Close()
        End If
    End Sub

    Private Sub tb_filename_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles tb_filename.Click
        MsgBox("Please put the complete name including file extention", MsgBoxStyle.Information, "Attention")
    End Sub

End Class
Hope you can help me... Thanks from now on for your time!...