C# MDI Child form textbox Ctrl+C not working

Hi,

I have a MDI and a child form.  On the child form, the Ctrl+C not working.
I search lots of solution and find the one on MSDN but not really working.

I put this code in the MDI code but no help, the send message does capture something but
SendMessage may send wrong parameter whatever, no idea how to make it work
I need Ctrl + c, Ctrl + V + Ctrl +x work on the text box in the child form.

Please help.

//I put this code in the MDI code but no help, the send message does capture something but
//SendMessage may send wrong parameter whatever, no idea how to make it work
 
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern IntPtr SendMessage(IntPtr hWnd, Int32 Msg, IntPtr wParam, IntPtr lParam);
 
 
        protected override bool ProcessCmdKey(ref Message message, Keys keydata)
        {
            SendMessage(this.ActiveMdiChild.Handle, message.Msg, message.WParam, message.LParam);
            return base.ProcessCmdKey(ref message, keydata);
        }

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