Save pictures while I scrape them from website using VB.NET - vb.net

Question

I find a code on YouTube when I use it on my visual basic and debug it and find pictures but when i want to save them software gives me this message here.
Private Sub btnSaveImages_Click(ByVal sender As _
System.Object, ByVal e As System.EventArgs) Handles _
btnSaveImages.Click
Dim dir_name As String = txtDirectory.Text
If Not dir_name.EndsWith("\") Then dir_name &= "\"
For Each pic As PictureBox In flpPictures.Controls
Dim bm As Bitmap = pic.Image
Dim filename As String = pic.Tag
filename = _
filename.Substring(filename.LastIndexOf("/") + _
1)
Dim ext As String = _
filename.Substring(filename.LastIndexOf("."))
Dim full_name As String = dir_name & filename
Select Case ext
Case ".bmp"
bm.Save(full_name, Imaging.ImageFormat.Bmp)
Case ".gif"
bm.Save(full_name, Imaging.ImageFormat.Gif)
Case ".jpg", "jpeg"
bm.Save(full_name, Imaging.ImageFormat.Jpeg)
Case ".png"
bm.Save(full_name, Imaging.ImageFormat.Png)
Case ".tiff"
bm.Save(full_name, Imaging.ImageFormat.Tiff)
Case Else
MessageBox.Show( _
"Unknown file type " & ext & _
" in file " & filename, _
"Unknown File Type", _
MessageBoxButtons.OK, _
MessageBoxIcon.Error)
End Select
Next pic
Beep()
End Sub

Answer 1

The issue is that LastIndexOf isn't finding . in your filename. This then passes -1 to to SubString which throws the error you're seeing.
Instead of writing the file parsing yourself use the methods of System.Io.Path such as
System.IO.Path.GetDirectoryName(filename)
System.IO.Path.GetFileName(filename)
System.IO.Path.GetFileNameWithoutExtension(filename)
Private Sub btnSaveImages_Click(ByVal sender As _
System.Object, ByVal e As System.EventArgs) Handles _
btnSaveImages.Click
For Each pic As PictureBox In flpPictures.Controls
Dim bm As Bitmap = pic.Image
Dim path As String = pic.Tag
Dim filename = IO.Path.GetFileName(path)
Dim ext = IO.Path.GetExtension(path)
Dim full_name = IO.Path.Combine(txtDirectory.txt, filename)
....