從資料庫準備輸入時Ping.SendAsync回傳空串列請求

我找到了一個代碼來檢查多個主機的連接性，這些主機從串列中讀取地址并以異步方式 ping 它們并處理結果。

當我使用預定義串列時，例如：

public static List<string> addresses = new List<string> { "172.20.74.1", "192.168.1.103", "192.168.1.104", "192.168.1.105"};

一切正常，但是當我從資料庫中讀取此串列時，發生 NullReferenceException。有人可以幫我解決這個問題嗎？

using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.NetworkInformation;
using System.Data.SqlClient;
using System.Collections.Generic;
using System;

namespace asyncPing
{
    class Program
    {
        public static List<string> addresses = getNetAddress();
        //public static List<string> addresses = new List<string> { "172.20.74.1", "192.168.1.103", "192.168.1.104", "192.168.1.105"};
        static void Main(string[] args)
        {
            List<Task<PingReply>> pingTasks = new List<Task<PingReply>>();

            foreach (var address in addresses)
            {
                Console.WriteLine(address);

            }
            foreach (var address in addresses)
            {
                pingTasks.Add(PingAsync(address));
            }

            //Wait for all the tasks to complete
            Task.WaitAll(pingTasks.ToArray());

            //Now you can iterate over your list of pingTasks
            foreach (var pingTask in pingTasks)
            {

                Console.WriteLine(pingTask.Result.Address   "\t"   pingTask.Result.Status);
                if (pingTask.Result.Status != IPStatus.Success)
                {
                    //Do Some Thing
                }
            }
            Console.ReadLine();
        }

        public static List<string> getNetAddress()
        {
            List<string> addr = new List<string>();
            string connetionString = @"Data Source=localhost;Initial Catalog=AlarmsDB;Persist Security Info=True;User ID=sa;Password=123456";



            using (SqlConnection myConnection = new SqlConnection(connetionString))
            {
                //Console.WriteLine("Connection Open  !");
                string oString = "Select ip_address from Networks";
                SqlCommand oCmd = new SqlCommand(oString, myConnection);

                myConnection.Open();
                using (SqlDataReader oReader = oCmd.ExecuteReader())
                {
                    while (oReader.Read())
                    {
                        addr.Add(oReader["ip_address"].ToString());
                    }

                    myConnection.Close();
                }
            }

            return addr;
        }
        static Task<PingReply> PingAsync(string address)
        {
            var tcs = new TaskCompletionSource<PingReply>();
            Ping ping = new Ping();
            ping.PingCompleted  = (obj, sender) =>
            {
                tcs.SetResult(sender.Reply);
            };
            ping.SendAsync(address, new object());
            return tcs.Task;
        }
    }
}

例外發生在：

Console.WriteLine(pingTask.Result.Address   "\t"   pingTask.Result.Status);

似乎 async pings 方法的結果似乎為空。我不知道為什么當從資料庫傳遞相同的輸入時，輸出的結果會發生變化？

uj5u.com熱心網友回復：

感謝所有家伙為解決問題提出的建議

最后我在 2 天后找到了問題根源

在將 ip 地址傳遞給 asyncPing 方法之前修剪了它之后，問題解決了。

我在資料庫中保存了ip地址為字串但不知道為什么我讀完后要修剪它們

我能夠通過更改以下行來解決問題：

using (SqlDataReader oReader = oCmd.ExecuteReader())
                {
                    while (oReader.Read())
                    {                        
                 addr.Add(oReader["ip_address"].ToString().Trim());
                    }

                    myConnection.Close();
                }

標籤：C＃ 异步 平

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