Introduction:
Hello and welcome to a tutorial on how to make a single file downloader in Visual Basic. A word of advise; once you understand how this program works I would recommend adding the function to a new thread so the UI doesn't freeze while it is downloading.

Steps of Creation:
Step 1:
First we want to get a direct download link to a file, you can get this by downloading a file then going to your download manager (in chrome, firefox or any other browser/application) and copying the download link that is shown, I will be using a direct download link from the official website to download the English Windows 64Bit WinRar Application (link: http://www.rarlab.com/rar/winrar-x64-500.exe)

Step 2:
Now make a form with a textbox (direct download link) and a button to begin the process. I have kept the default names of textbox1 and button1 as we can easily tell the difference.

Step 3:
Next double click on button1 to get to the clicked event code, and add this:

1. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
2. Dim
   
   url As
   
   String
   
   = checkURL()
   
3. Try
   
4. Dim
   
   fo As
   
   New
   
   SaveFileDialog
   
5. fo.Filter = "Executable File|.exe|All Files|*"
   
6. fo.FilterIndex = 1
   
7. fo.RestoreDirectory = True
   
8. fo.ShowDialog()
   
9. Dim
   
   path As
   
   String
   
   = fo.FileName
   
10. My.Computer.Network.DownloadFile(url, path)
    
11. MsgBox("Finished!"
    
    )
    
12. Catch ex As
    
    Exception
    
13. MsgBox("Failed"
    
    )
    
14. End
    
    Try
    
15. End
    
    Sub
    

First we are getting the returned string from a function which we have not yet created called "checkURL" which is going to check the download link is in the correct format. Once it has the URL it is going to ask for a save location path and name and download the file to that directory. If it goes successfully it will output "Finished!", otherwise it will output "Failed".

Step 4:
Finally we want to make our checkURL function. As mentioned above, it will check the direct download link is in the correct format.

1. Private
   
   Function
   
   checkURL()
   
2. Dim
   
   s As
   
   String
   
   = TextBox1.Text.ToLower()
   
3. If
   
   (s.StartsWith("http://www."
   
   ) Or
   
   s.StartsWith("https://www."
   
   )) Then
   
4. Return s
   
5. ElseIf
   
   (s.StartsWith("http://"
   
   )) Then
   
6. If
   
   (s.Contains("www."
   
   )) Then
   
7. s = "http://www."
   
   & s.Substring(1, s.Count - 1)
   
8. TextBox1.Text = s
   
9. Return s
   
10. Else
    
11. s = "http://www."
    
    & s.Substring(7, s.Count - 7)
    
12. TextBox1.Text = s
    
13. Return s
    
14. End
    
    If
    
15. ElseIf
    
    (s.StartsWith("https://"
    
    )) Then
    
16. If
    
    (s.Contains("www."
    
    )) Then
    
17. s = "https://"
    
    & s.Substring(12, s.Count() - 12)
    
18. TextBox1.Text = s
    
19. Return s
    
20. Else
    
21. s = "https://www."
    
    & s.Substring(8, s.Count - 8)
    
22. TextBox1.Text = s
    
23. Return s
    
24. End
    
    If
    
25. Else
    
26. If
    
    (s.StartsWith("www."
    
    )) Then
    
27. s = "http://www."
    
    & s.Substring(4, s.Count() - 4)
    
28. TextBox1.Text = s
    
29. Return s
    
30. Else
    
31. s = "http://www."
    
    & s
    
32. TextBox1.Text = s
    
33. Return s
    
34. End
    
    If
    
35. End
    
    If
    
36. End
    
    Function
    

Project Complete!
Below is the full source and download to the files...

1. Public
   
   Class Form1
   
2. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
3. Dim
   
   url As
   
   String
   
   = checkURL()
   
4. Try
   
5. Dim
   
   fo As
   
   New
   
   SaveFileDialog
   
6. fo.Filter = "Executable File|.exe|All Files|*"
   
7. fo.FilterIndex = 1
   
8. fo.RestoreDirectory = True
   
9. fo.ShowDialog()
   
10. Dim
    
    path As
    
    String
    
    = fo.FileName
    
11. My.Computer.Network.DownloadFile(url, path)
    
12. MsgBox("Finished!"
    
    )
    
13. Catch ex As
    
    Exception
    
14. MsgBox("Failed"
    
    )
    
15. End
    
    Try
    
16. End
    
    Sub
    
17. 
    
18. Private
    
    Function
    
    checkURL()
    
19. Dim
    
    s As
    
    String
    
    = TextBox1.Text.ToLower()
    
20. If
    
    (s.StartsWith("http://www."
    
    ) Or
    
    s.StartsWith("https://www."
    
    )) Then
    
21. Return s
    
22. ElseIf
    
    (s.StartsWith("http://"
    
    )) Then
    
23. If
    
    (s.Contains("www."
    
    )) Then
    
24. s = "http://www."
    
    & s.Substring(1, s.Count - 1)
    
25. TextBox1.Text = s
    
26. Return s
    
27. Else
    
28. s = "http://www."
    
    & s.Substring(7, s.Count - 7)
    
29. TextBox1.Text = s
    
30. Return s
    
31. End
    
    If
    
32. ElseIf
    
    (s.StartsWith("https://"
    
    )) Then
    
33. If
    
    (s.Contains("www."
    
    )) Then
    
34. s = "https://"
    
    & s.Substring(12, s.Count() - 12)
    
35. TextBox1.Text = s
    
36. Return s
    
37. Else
    
38. s = "https://www."
    
    & s.Substring(8, s.Count - 8)
    
39. TextBox1.Text = s
    
40. Return s
    
41. End
    
    If
    
42. Else
    
43. If
    
    (s.StartsWith("www."
    
    )) Then
    
44. s = "http://www."
    
    & s.Substring(4, s.Count() - 4)
    
45. TextBox1.Text = s
    
46. Return s
    
47. Else
    
48. s = "http://www."
    
    & s
    
49. TextBox1.Text = s
    
50. Return s
    
51. End
    
    If
    
52. End
    
    If
    
53. End
    
    Function
    
54. End
    
    Class
    

Note: Due to the size or complexity of this submission, the author has submitted it as a .zip file to shorten your download time. After downloading it, you will need a program like Winzip to decompress it.

Virus note: All files are scanned once-a-day by SourceCodester.com for viruses, but new viruses come out every day, so no prevention program can catch 100% of them.

FOR YOUR OWN SAFETY, PLEASE:

1. Re-scan downloaded files using your personal virus checker before using it.

2. NEVER, EVER run compiled files (.exe's, .ocx's, .dll's etc.)--only run source code.

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