Visual Basic 2012 File Downloader

[kostakostvb]

Hello,
I am creating a file downloader in Visual Basic 2012.
It works well, but when I click the red X button, it closes whether the download has finished or not. Thus,
I am looking for code that disables the X button at a certain time. I mean, I do not want it always disabled,
just when a file is being downloaded.
What is more, I am also looking for a code for creating
a Cancel button (to cancel file download).

Here's the file download code:

Imports System.Net
Private WithEvents httpclient As WebClient

Private Sub DownloadButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DownloadButton.Click
        
    httpclient = New WebClient
    Dim sourceURL = TextBox1.Text
    Dim filedir = TextBox2.Text
    ProgressBar1.Value = 0
    ProgressBar1.Maximum = 100
            
    Try
        httpclient.DownloadFileAsync(New Uri(sourceURL), (filedir))
            
    Catch ex As Exception
            
        MessageBox.Show("Error while  downloding", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                
    End Try
End Sub

Grateful for any reply. Thank in advance