防止从只读RichTextBox中闪烁光标(IBeam)

protected override void WndProc(ref Message m)
{
    const int WM_SETFOCUS = 0x0007;
    const int WM_KILLFOCUS = 0x0008;
    const int WM_MOUSEACTIVATE = 0x0021;
    const int WM_IME_SETCONTEXT = 0x0281;
    const int WM_IME_NOTIFY = 0x0282;
    const int WM_IME_COMPOSITION = 0x010F;
    const int WM_IME_STARTCOMPOSITION = 0x010D;
    const int WM_IME_ENDCOMPOSITION = 0x010E;

    if (m.Msg == WM_SETFOCUS || m.Msg == WM_KILLFOCUS || m.Msg == WM_MOUSEACTIVATE || m.Msg == WM_IME_SETCONTEXT || m.Msg == WM_IME_NOTIFY || m.Msg == WM_IME_COMPOSITION || m.Msg == WM_IME_STARTCOMPOSITION || m.Msg == WM_IME_ENDCOMPOSITION)
    {
        return;
    }

    base.WndProc(ref m);
}

richTextBox1.ReadOnly = true;