目录和子目录中的文件列表

我正在使用以下代码。但它无法在文本框t1中传递输出。

Imports System.IO

Public Class Form1
Dim fp As String

Private Sub b1_Click(sender As Object, e As EventArgs) Handles b1.Click
    If (FolderBrowserDialog1.ShowDialog() = DialogResult.OK) Then
        fp = FolderBrowserDialog1.SelectedPath
        t2.Text = fp
    End If

End Sub

Private Sub b2_Click(sender As Object, e As EventArgs) Handles b2.Click
    Dim filelist As String() = Directory.GetFiles(fp, SearchOption.AllDirectories)

    For Each filename As String In filelist
        t1.AppendText(filename)
    Next

End Sub

我无法查出错误在哪里。需要帮助