WindowHelper.WinAPI.GetWindowLong C# (CSharp) Метод

        internal static extern int GetWindowLong(IntPtr hWnd, int nIndex);

        public void AddBorder()
        {
            int style = WinAPI.GetWindowLong(this.Handle, WinAPI.GWL_STYLE);

            WinAPI.SetWindowLong(this.Handle, WinAPI.GWL_STYLE, (style & WinAPI.WS_THICKFRAME));
        }