Disable Close button

I'm not sure if someone else has beaten me to it because I couldn't be bothered searching too hard, but here is a method to disable the Close button in the title bar and the Close option of the system menu of a form.

Code:

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                private const int SC_CLOSE = 0xF060;
                private const int MF_GRAYED = 0x1;

                [DllImport("user32.dll")]
                private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

                [DllImport("user32.dll")]
                private static extern int EnableMenuItem(IntPtr hMenu, int wIDEnableItem, int wEnable);

                private void Form1_Load(object sender, System.EventArgs e)
                {
                        EnableMenuItem(GetSystemMenu(this.Handle, false), SC_CLOSE, MF_GRAYED);
                }

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