从 arduino 获取串行输出的奇怪行为

Question

I made an Arduino script for printing key on button press :

#include <Keypad.h>

//Buttons
const byte ROWS = 2;
const byte COLS = 2;
char keys[ROWS][COLS] = {
    {'1','2'},
    {'3','4'}
};
byte rowPins[ROWS] = {A0, A1};
byte colPins[COLS] = {30, 31};
Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

void setup() {
    Serial.begin(9600);
    keypad.addEventListener(keypadEvent);
}

void loop() {
    char key = keypad.getKey();
}

void keypadEvent(KeypadEvent key){
    switch (keypad.getState()){
        case PRESSED:
            Serial.println(key);
            break;
        default:
            break;
    }
}

Then, I made a C# code for printing it in debug console (for testing before going further) :

using System;
using System.Diagnostics;
using System.IO.Ports;

namespace ConsoleApplication1
{
    class Program
    {
        public static void Main()
        {
            SerialPort SP = new SerialPort("COM3");

            SP.BaudRate = 9600;
            SP.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);

            SP.Open();
            Console.WriteLine("Press any key to continue...");
            Console.WriteLine();
            Console.ReadKey();
            SP.Close();
        }

        private static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
        {
            SerialPort SP = (SerialPort)sender;
            string msg = SP.ReadExisting();
            Debug.Print($"Data Received: {msg}");
        }
    }
}

When using Arduino's serial monitor I get the good behavior :

But when using my console app, I sometime get empty lines :

Any ideas on how to improve it ?

Answer 1

Jasc24 got me on the way. SerialPort.ReadExisting() reads a stream that can be unfinished and the SerialDataReceivedEventHandler can fire multiple times for a single line.

My workaround was the following :

class Program
{
    static string line = string.Empty;

    public static void Main()
    {
        SerialPort SP = new SerialPort("COM3");

        SP.BaudRate = 9600;
        SP.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);

        SP.Open();
        Console.WriteLine("Press any key to continue...");
        Console.WriteLine();
        Console.ReadKey();
        SP.Close();
    }

    private static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
    {
        SerialPort SP = (SerialPort)sender;
        line = $"{line}{SP.ReadExisting()}";
        if (line.Contains(Environment.NewLine))
        {
            line = line.Replace(Environment.NewLine, string.Empty);
            Debug.Print($"Data Received: {line}");
            line = string.Empty;
        }            
    }
}

Waiting for the EOL characters to be sure that I got the all line before printing it.