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           // if true, no form painting will be allowed
           bool _paintDisabled;

...

           public MainForm()
           {
                      if (!this.DesignMode)
                                 _paintDisabled = true;

                      InitializeComponent();
           }


...

           protected override void OnLoad(EventArgs e)
           {
                      base.OnLoad(e);

                      if (this.DesignMode) return;

                      // force form to be refreshed once, but because it flickers - do it via WM_PRINT WinAPI message
                      using (Graphics gr = this.CreateGraphics())
                      {
                                 IntPtr hdc = gr.GetHdc();
                                 try
                                 {
                                            int parameters = (int)(PRF_CHILDREN | PRF_NONCLIENT | PRF_CLIENT);
                                            SendMessage(this.Handle, WM_PRINT, hdc, parameters);
                                 }
                                 finally
                                 {
                                            gr.ReleaseHdc(hdc);
                                            _paintDisabled = false;
                                 }
                      }
           }

...

        protected override void WndProc(ref Message m)
        {
            if (_paintDisabled)
            {
                int msg = m.Msg;
                if (msg == WM_PAINT || msg == WM_PAINTCLIPBOARD || msg == WM_PAINTICON
                    || msg == WM_ERASEBKGND)
                {
                    m.Result = IntPtr.Zero;
                    return;
                }
            }

            base.WndProc(ref m);
        }

        private const UInt32 WM_PAINT = 0x000F;
        private const UInt32 WM_NCPAINT = 0x0085;
        private const UInt32 WM_PAINTCLIPBOARD = 0x0309;
        private const UInt32 WM_PAINTICON = 0x0026;
        private const UInt32 WM_ERASEBKGND = 0x0014;
        private const UInt32 WM_PRINT = 0x0317;
        private const UInt32 WM_PRINTCLIENT = 0x0318;
        const int WM_SYSKEYDOWN = 260;

        private const uint PRF_CHECKVISIBLE = 0x00000001;
        private const uint PRF_NONCLIENT = 0x00000002;
        private const uint PRF_CLIENT = 0x00000004;
        private const uint PRF_ERASEBKGND = 0x00000008;
        private const uint PRF_CHILDREN = 0x00000010;
        private const uint PRF_OWNED = 0x00000020;

        [DllImport("User32.dll")]
        public static extern int SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, int lParam);

...