How Can I Eliminate Flickering When Highlighting Text in a RichTextBox During Real-Time Input?

Extended Syntax Highlighting for RichTextBox: Disabling Repaint for Flicker-Free Input

As you type text into a RichTextBox control, you may want to highlight specific keywords or undesirable words in real time. To achieve this, a function is typically invoked with each keystroke, which can result in excessive flickering of words and the cursor.

In this context, disabling repaint is a proposed solution to minimize visual distractions. One method to do this is by overriding the "WndProc" function and intercepting the repaint message. However, if the function you're using requires passing a RichTextBox parameter, this approach becomes challenging.

An alternative solution is to leverage the "BeginUpdate" and "EndUpdate" methods, which allow you to suppress painting and trigger it once you're done modifying the text. Unfortunately, these methods are not exposed in the RichTextBox class.

To address this oversight, you can add these methods yourself by creating a custom class that inherits from RichTextBox. Paste the following code into a new class added to your project:

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;
}

Once compiled, drop the MyRichTextBox control onto your form from the toolbox. Alternatively, you can call the SendMessage function directly with the WM_SETREDRAW message before and after updating the RichTextBox text.

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