為什么緩沖區為空？

Question

我正在嘗試檢查一些在GSM調制解調器上運行的AT命令的值。 我陷入了試圖檢查命令輸出是否包含某些值的情況。

使用以下代碼：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO.Ports;
using System.IO;
using System.Timers;


namespace SerialTest
{
    public class Program
    {

        public static void Main(string[] args)
        {
            string buff="0";
            string ok = "OK";

            SerialPort p = new SerialPort("COM28");
            p.DataReceived += new SerialDataReceivedEventHandler(p_DataReceived);
            p.Open();
            string line = "1";
            p.Write("AT" + "\r");
            buff = p.ReadExisting();
            Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
            p.Write("AT+CMGF=1"+ "\r" );
            buff = p.ReadExisting();
            Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
            do
            {
                p.Write("AT+CMGL=\"REC UNREAD\" " + "\r");
                buff = p.ReadExisting(); 
                Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
                /*if (buff.Contains(ok))
                    Console.WriteLine("Everything is OK");
                else
                    Console.WriteLine("NOK");*/
                line = Console.ReadLine();
            } while (line != "quit");
            p.Close();
        }

        public static void p_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {

            Console.WriteLine((sender as SerialPort).ReadExisting());
        }
    }
}

我得到以下輸出：

為什么有時buff為空並稍后顯示？

Answer 1

有多余的對ReadExisting()調用。 您不應該在main方法中讀取串行端口輸出，讓事件處理程序為您完成工作。 同樣，您應該將在事件處理程序中讀取的內容追加到buff變量，以便檢查緩沖區時可以接收到的所有數據。

嘗試以下方法：

public class Program
{
    public static void Main(string[] args)
    {
        ModemReader r = new ModemReader();
        r.StartReading();
    }
    class ModemReader{
        string buff="";
        public void StartReading()
        {
            string ok = "OK";
            SerialPort p = new SerialPort("COM28");
            p.DataReceived += new SerialDataReceivedEventHandler(p_DataReceived);
            p.Open();
            string line = "1";
            p.Write("AT" + "\r");
            Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
            p.Write("AT+CMGF=1"+ "\r" );
            Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
            do
            {
                // Clear the buffer here
                buff = "";  

                p.Write("AT+CMGL=\"REC UNREAD\" " + "\r");
                Console.WriteLine("buff: \"{0}\"\nok: \"{1}\"", buff, ok);
                if (buff.Contains(ok))
                    Console.WriteLine("Everything is OK");
                else
                    Console.WriteLine("NOK");
                line = Console.ReadLine();
            } while (line != "quit");
            p.Close();
        }
        public void p_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            string s = (sender as SerialPort).ReadExisting();
            buff += s;
            Console.WriteLine(s);
        }
    }
} 

Answer 2

您只能使用一次端口數據。 因為您在處理程序中使用了它，所以當您嘗試將其放入緩沖區時，它不再存在。