Introduction:
This tutorial is on how to make a simple Notepad text editor in Visual Basic .NET.

Controls:
The controls we will need are;
Button, button1, Save File
Button, button2, Open File
Textbox, textbox1, File Contents

Imports:
Before we begin, you need to import System.IO to allow our program to read and write to/from files. Put this at the top of your document...

1. Imports System.IO
   

Open File:
For the open file button, we are first going to create a temporary (using) OpenFileDialog box, and give it some basic properties...

1. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
2. Using fo As
   
   New
   
   OpenFileDialog
   
3. fo.Multiselect = False
   
4. fo.RestoreDirectory = True
   
5. fo.ShowDialog()
   
6. End
   
   Using
   
7. End
   
   Sub
   

We then show the dialog which allows the user to select a file to open. The 'ShowDialog()' function is a call blocking function so the code will pause while the user is selecting a file.

Once the file is selected, we first ensure that the user didn't click 'Close' by checking for a null/empty/nothing filename...

1. If
   
   (Not
   
   fo.FileName = Nothing
   
   ) Then
   
2. 
   
3. End
   
   If
   

If it is a valid file, we read the contents to our textbox, 'textbox1'...

1. TextBox1.Text = File.ReadAllText(fo.FileName)
   

Save File:
To save our file, we use a similar procedure to our open file script. Except we use a SaveFileDialog box instead of an OpenFileDialog box.

1. Private
   
   Sub
   
   Button2_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button2.Click
   
2. Using fs As
   
   New
   
   SaveFileDialog
   
3. fs.RestoreDirectory = True
   
4. fs.Filter = "Text Files|*.txt"
   
5. fs.FilterIndex = 1
   
6. fs.ShowDialog()
   
7. If
   
   Not
   
   (fs.FileName = Nothing
   
   ) Then
   
   File.WriteAllText(fs.FileName, TextBox1.Text)
   
8. End
   
   Using
   
9. End
   
   Sub
   

Filters:
We could also limit our user to only saving .txt files by adding filters to our Open/Save FileDialog boxes, like so...

1. fo.Filter = "Text Files|*.txt"
   
2. fo.FilterIndex = 1
   

(Replace 'fo' with 'fs' for the saving script. Above is the open script.)

Finished!
Here is the full source code...

1. Imports System.IO
   
2. 
   
3. Public
   
   Class Form1
   
4. 
   
5. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
6. Using fo As
   
   New
   
   OpenFileDialog
   
7. fo.Multiselect = False
   
8. fo.RestoreDirectory = True
   
9. fo.Filter = "Text Files|*.txt"
   
10. fo.FilterIndex = 1
    
11. fo.ShowDialog()
    
12. If
    
    (Not
    
    fo.FileName = Nothing
    
    ) Then
    
13. TextBox1.Text = File.ReadAllText(fo.FileName)
    
14. End
    
    If
    
15. End
    
    Using
    
16. End
    
    Sub
    
17. 
    
18. Private
    
    Sub
    
    Button2_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button2.Click
    
19. Using fs As
    
    New
    
    SaveFileDialog
    
20. fs.RestoreDirectory = True
    
21. fs.Filter = "Text Files|*.txt"
    
22. fs.FilterIndex = 1
    
23. fs.ShowDialog()
    
24. If
    
    Not
    
    (fs.FileName = Nothing
    
    ) Then
    
    File.WriteAllText(fs.FileName, TextBox1.Text)
    
25. End
    
    Using
    
26. End
    
    Sub
    
27. End
    
    Class