How to Eliminate RichTextBox Flickering During Syntax Highlighting?

Disabling Repaint for RichTextBox Syntax Highlighting

When performing syntax highlighting in a RichTextBox during user input, resolving flickering requires disabling repainting.

Current Inefficient Solution

The current solution involves overriding the "WndProc" function to intercept and suppress repaint messages. However, this approach is not practical for external functions working with a provided RichTextBox.

Overcoming the Oversight

A more effective approach is to add the missing BeginUpdate and EndUpdate methods to the RichTextBox class. These methods generate the WM_SETREDRAW message to suppress repainting.

Adding the Methods

Create a new class in your project with the following code:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class MyRichTextBox : RichTextBox {
    public void BeginUpdate() {
        SendMessage(this.Handle, WM_SETREDRAW, (IntPtr)0, IntPtr.Zero);
    }
    public void EndUpdate() {
        SendMessage(this.Handle, WM_SETREDRAW, (IntPtr)1, IntPtr.Zero); 
        this.Invalidate();
    }
    [DllImport("user32.dll")]
    private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
    private const int WM_SETREDRAW = 0x0b;
}

Usage

You can now use these methods to disable and enable repainting within your syntax highlighting function.

Alternative Solution

If adding the methods to the class is not possible, you can also use the P/Invoke "SendMessage" function directly before and after updating the text.

SendMessage(this.Handle, WM_SETREDRAW, (IntPtr)0, IntPtr.Zero); // Disable repainting
// Update text
SendMessage(this.Handle, WM_SETREDRAW, (IntPtr)1, IntPtr.Zero); // Enable repainting
this.Invalidate();

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