Top Features to Add to Your VB .NET Notepad Application

VB .NET Notepad: Implementing Syntax Highlighting and Line Numbers

Creating a Notepad-like application in VB .NET is a great way to learn Windows Forms and text handling. Adding syntax highlighting and line numbers makes it far more useful for code editing. This article walks through a concise, practical implementation using Windows Forms (WinForms) and a RichTextBox control with minimal external dependencies.

Overview

• Goal: A simple Notepad with syntax highlighting for a chosen language (example: VB.NET keywords) and a live line-number gutter.
• Approach: Use a RichTextBox for editable text, a Panel/Label or a separate read-only RichTextBox for the line-number gutter, and a keyword-based highlighting routine that updates on text changes and caret moves.
• Assumptions: Targeting .NET Framework or .NET (Windows) with WinForms; familiarity with VB .NET and basic event handling.

Project setup

1. Create a new Windows Forms App (VB .NET).
2. Add controls to the main form:
   • RichTextBox named rtbEditor (Dock = Fill).
   • Panel named pnlGutter docked Left to host line numbers (Width ≈ 50).
   • (Optional) A read-only RichTextBox named rtbGutter inside pnlGutter for easier synchronization.
3. Set rtbEditor.AcceptsTab = True, rtbEditor.Font to a monospaced font (e.g., Consolas).

Line numbers: design and sync

Method: Use a read-only RichTextBox (rtbGutter) aligned with rtbEditor so scrolling and line wrapping appear consistent.

Key steps:

• Keep rtbGutter read-only, same Font as rtbEditor, BackColor slightly different, BorderStyle = None.
• Update gutter text whenever rtbEditor content or scroll position changes.

Core routine (conceptual VB .NET code):

vb
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’ Call this on Form Load and whenever text or layout changes Private Sub UpdateLineNumbers()Dim lines As Integer = rtbEditor.Lines.Length

 
Dim sb As New System.Text.StringBuilder() For i As Integer = 1 To lines     sb.AppendLine(i.ToString()) Next rtbGutter.Text = sb.ToString() 
End Sub 

Sync scrolling:

Handle rtbEditor.VScroll (no built-in event; use Win32 message or a timer) or rtbEditor.SelectionChanged to align the gutter’s first visible line.
Simpler approach: set rtbGutter.SelectionStart = rtbEditor.GetCharIndexFromPosition(New Point(0,0)) and call rtbGutter.ScrollToCaret() to match vertical position.

Example helper to scroll gutter (simplified):
vb
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Private Sub SyncGutterScroll()     Try

 
    Dim index As Integer = rtbEditor.GetCharIndexFromPosition(New Point(0, 0))     rtbGutter.SelectionStart = index     rtbGutter.ScrollToCaret() Catch ex As Exception     ' ignore End Try 
End Sub 

Call UpdateLineNumbers() and SyncGutterScroll() from:

rtbEditor.TextChanged
rtbEditor.SelectionChanged
Form Resize

Performance tip: For large documents, avoid rebuilding the entire gutter on every keystroke. Use a short debounce timer (e.g., 100–200 ms) to batch updates.
Syntax highlighting: keyword-based approach
We’ll implement a fast, simple highlighter that colors VB .NET keywords and comments. This is not a full lexer but works well for small-to-medium files.
Design decisions:

Use RichTextBox’s selection-based formatting (fast enough for moderate sizes).
Preserve user selection and scroll position while applying formatting.
Use Regex to locate tokens: keywords, comments, strings.

Example keywords list (partial):
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Dim keywords As String() = {“Module”,“Sub”,“Function”,“Dim”,“As”,“If”,“Then”,“Else”,“End”,“For”,“Next”,“While”,“Return”,“Public”,“Private”,“Class”,“New”} 
Highlighting routine (conceptual):
vb
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Private Sub HighlightSyntax()     ‘ Remember selection and scroll

 
Dim selStart = rtbEditor.SelectionStart Dim selLength = rtbEditor.SelectionLength Dim viewportIndex = rtbEditor.GetCharIndexFromPosition(New Point(1,1)) ' Disable redrawing for smoother visual update SendMessage(rtbEditor.Handle, WM_SETREDRAW, False, 0) ' Reset all text color to default rtbEditor.SelectAll() rtbEditor.SelectionColor = Color.Black ' Highlight comments (single-line starting with ') Dim commentPattern As String = "'.*$" For Each m As Match In Regex.Matches(rtbEditor.Text, commentPattern, RegexOptions.Multiline)     rtbEditor.Select(m.Index, m.Length)     rtbEditor.SelectionColor = Color.Green Next ' Highlight strings Dim stringPattern As String = """([^""]|"""")*""" For Each m As Match In Regex.Matches(rtbEditor.Text, stringPattern)     rtbEditor.Select(m.Index, m.Length)     rtbEditor.SelectionColor = Color.Brown Next ' Highlight keywords (word boundaries) For Each kw As String In keywords     Dim pattern As String = "" & Regex.Escape(kw) & ""     For Each m As Match In Regex.Matches(rtbEditor.Text, pattern, RegexOptions.IgnoreCase)         rtbEditor.Select(m.Index, m.Length)         rtbEditor.SelectionColor = Color.Blue     Next Next ' Restore selection and redraw rtbEditor.Select(selStart, selLength) SendMessage(rtbEditor.Handle, WM_SETREDRAW, True, 0) rtbEditor.Invalidate() ' Restore viewport rtbEditor.SelectionStart = viewportIndex rtbEditor.ScrollToCaret() 
End Sub 

Notes:

WMSETREDRAW is used to prevent flicker during formatting. Import via:


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 _ Private Shared Function SendMessage(hWnd As IntPtr, wMsg As Integer, wParam As Boolean, lParam As Integer) As Integer End Function Private Const WM_SETREDRAW As Integer = 11 

Preserve user selection so typing isn’t disrupted.

Performance strategies:

Highlight only visible text range instead of entire document for large files. Use GetCharIndexFromPosition and measure visible lines.
Use a background worker or Task to compute token positions, then marshal formatting back to UI thread.
Cache regex matches when possible; re-run only on changed lines.

Handling editing and caret movement

Trigger highlighting on TextChanged with debounce, and minor updates on KeyUp for quick feedback.
Update line numbers and gutter sync on the same events.
For multi-threaded highlighting, ensure all RichTextBox updates run on the UI thread (Invoke/BeginInvoke).

Optional enhancements

Add brace matching (highlight matching parentheses).
Implement auto-indentation on Enter key.
Add customizable themes (colors, font) via settings.
Use a third-party text editor control (e.g., ScintillaNET) for robust editing features if you need high performance and full language support.

Example wiring (events)

rtbEditor.TextChanged -> Start debounce timer -> HighlightSyntax + UpdateLineNumbers + SyncGutterScroll
rtbEditor.SelectionChanged -> SyncGutterScroll
Form.Resize -> UpdateLineNumbers + SyncGutterScroll

Final notes
This approach gives a lightweight VB .NET Notepad with basic syntax highlighting and line numbers using built-in controls. For production-grade editors with large files and advanced language features, prefer specialized controls like ScintillaNET or AvalonEdit (WPF) which provide built-in lexing, folding, and much better performance.
If you want, I can provide a complete sample project (full VB .NET code files) implementing the routines above.