VB 2010 getfilename

Ich habe mir ein kleines download tool geschrieben komm aber nicht weiter...
ich will den filename abfragen bekomm das aber irgendwie nicht hin hab schon endliche foren etc durchsucht aber komm nicht weiter

Kompletter Code:

Code:

Imports System.Net
Imports System.IO

Public Class Form1

    Public WithEvents downloader As WebClient
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        downloader = New WebClient
        downloader.DownloadFileAsync(New Uri(TextBox1.Text), 123)
        Me.Button1.Enabled = False
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim speichern = New FolderBrowserDialog
        speichern.ShowDialog()
        Me.TextBox2.Text = speichern.SelectedPath
    End Sub

    Private Sub downloader_DownloadFileCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs) Handles downloader.DownloadFileCompleted
        MsgBox("Download beendet", MsgBoxStyle.Information, "Fertig!")
        Me.ProgressBar1.Value = 0
        Me.Label3.Text = "0 von 0 bytes"
        Me.Label4.Text = "0%"
        Me.Button1.Enabled = True
    End Sub

    Private Sub downloader_DownloadProgressChanged(ByVal sender As Object, ByVal e As System.Net.DownloadProgressChangedEventArgs) Handles downloader.DownloadProgressChanged
        Me.ProgressBar1.Value = e.ProgressPercentage
        Me.Label3.Text = e.BytesReceived & "Von " & e.TotalBytesToReceive & "Bytes"
        Me.Label4.Text = e.ProgressPercentage & "%"
    End Sub
End Class

Mein Problem:

Code:

 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        downloader = New WebClient
        downloader.DownloadFileAsync(New Uri(TextBox1.Text), Hier muss der file name hin)
        Me.Button1.Enabled = False
    End Sub