串口响应缓冲区 null 问题 C#

Question

I am trying to make a small Console program in C# which mimics a hardware where the it responses a particular sent command in a master slave fashion. So another program(master) will send a byte array for example: 0xFF, 0x00, 0xCD, 0x01, 0x00, 0x00, 0x00; and the slave Console program I try to make will check this received byte array and if its third element is 0xCD then it will respond as 0xFF, 0x00, 0xCD, 0x01, 0x00, 0x00, 0x00.

Here is the entire program I tried:

using System.IO.Ports;
namespace ConsoleMyConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            SerialPort myPort = new SerialPort();

            byte[] message_to_receive = null;
            byte[] message_to_response = { 0xFF, 0x00, 0xCD, 0x01, 0x00, 0x00, 0x00 };
            myPort.PortName = "COM8";
            myPort.BaudRate = 9600;
            myPort.DataBits = 8;
            myPort.Parity = Parity.None;
            myPort.StopBits = StopBits.One;

            myPort.Open();

            int received_bytes = myPort.BytesToRead;
            myPort.Read(message_to_receive, 0, received_bytes);

            if (message_to_receive[2] == 0xCD)
                myPort.Write(message_to_response, 0, message_to_response.Length);
        }
    }
}

But when I run this program I get: System.ArgumentNullException: 'Buffer cannot be null error. I dont know why is this happening at myPort.Read. I have to declare message_to_receive anyway, and couldn't make it work.

Answer 1

See this specification page.
SerialPort.Read Method

For the buffer array specified in the parameter of the Read(), an area of the size required by the calling application must be prepared in advance.
Unlike ReadExisting(), ReadLine(), and ReadTo(), the API does not prepare the character string data.

Prepare an array with the longest data size that can occur, or prepare an array with a short size and repeat Read() as many times as necessary.