How Can I Efficiently Suspend and Resume RichTextBox Repainting for Live Syntax Highlighting?

Suspending Repaint in RichTextBox for Live Syntax Highlighting

To efficiently highlight keywords in a RichTextBox in real time, it's ideal to disable the control's automatic repainting. While the WndProc override method allows for this, it's not suitable for an external function that takes a RichTextBox.

Fortunately, there's a workaround that leverages the SendMessage API to directly control the automatic repainting:

[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);

private const int WM_SETREDRAW = 0x0b;

By calling SendMessage with wp set to 0, automatic repainting is disabled. Conversely, setting wp to 1 re-enables it.

Usage:

1. Begin repainting suspension: SendMessage(richTextBoxHandle, WM_SETREDRAW, (IntPtr)0, IntPtr.Zero);
2. Perform text updates and formatting.
3. Resume repainting: SendMessage(richTextBoxHandle, WM_SETREDRAW, (IntPtr)1, IntPtr.Zero);
4. Invalidate the control to trigger an immediate repaint: richTextBoxHandle.Invalidate();

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