Category: Windows Development

If you get this message during compilation, right click on the solution and select Configuration Manager. For the build configuration you have selected, check the box of the project that compiler complained about.

Very often, I want to disable the X button on a windows form so I can control what happens when a user closes the form. The following code has been working great for dialogs.

        public static extern int ExitWindowsEx(int uFlags, int dwReason);

        [DllImport("user32.dll", EntryPoint = "GetSystemMenu")]
        private static extern IntPtr GetSystemMenu(IntPtr hwnd, int revert);

        [DllImport("user32.dll", EntryPoint = "GetMenuItemCount")]
        private static extern int GetMenuItemCount(IntPtr hmenu);

        [DllImport("user32.dll", EntryPoint = "RemoveMenu")]
        private static extern int RemoveMenu(IntPtr hmenu, int npos, int wflags);

        [DllImport("user32.dll", EntryPoint = "DrawMenuBar")]
        private static extern int DrawMenuBar(IntPtr hwnd);

        private const int MF_BYPOSITION = 0x0400;
        private const int MF_DISABLED = 0x0002;

        public MainForm()

            IntPtr hmenu = GetSystemMenu(this.Handle, 0);
            int cnt = GetMenuItemCount(hmenu);

            // remove 'close' action
            RemoveMenu(hmenu, cnt-1, MF_DISABLED | MF_BYPOSITION);

            // remove extra menu line
            RemoveMenu(hmenu, cnt - 2, MF_DISABLED | MF_BYPOSITION);


However, the above code doesn’t work when the form is the main window of the program. So, I find the following method more robust.

        protected override CreateParams CreateParams
                CreateParams cp = base.CreateParams;
                const int CS_NOCLOSE = 0x200;
                cp.ClassStyle = cp.ClassStyle | CS_NOCLOSE;
                return cp;