获取C＃BackgroundWorker进程以调用Ping

Question

Read through most (all?) of the answered questions regarding the C# BackgroundWorker but none seemed to apply to this situation. If I missed one, please point me in that direction!

Anyway, I having troubles getting the Ping process to run as a background process. I made a simple form application to send pings and report back. That worked fine but it would only results results to the user after the pings were complete -- thus the need to a background process. I am somewhat new to C# and was unfamiliar with the particulars of BackgroundWorker. However found a helpful walkthrough from Microsoft here: http://msdn.microsoft.com/en-us/library/ywkkz4s1.aspx

I am now attempting to get the same process to apply to a System.Net.NetworkInformation object instead of a System.IO.StreamReader object. I think I am really close (read: I can get the app to build and run) but I consistently get an error at runtime (see below).

This is the Microsoft code for their sample app. It works like a champ:

The method in MainForm.cs that calls the Words.cs class referenced in the walkthrough

void backgroundWorker1DoWork(object sender, DoWorkEventArgs e)
    {
        System.ComponentModel.BackgroundWorker worker;
        worker = (System.ComponentModel.BackgroundWorker)sender;
        Words WC = (Words)e.Argument;
        WC.CountWords(worker, e);
    }

The relevant method in the 'Words.cs' class

   public void CountWords(
        System.ComponentModel.BackgroundWorker worker,
        System.ComponentModel.DoWorkEventArgs e)
    {
        // Initialize the variables.
        CurrentState state = new CurrentState();
        string line = "";
        int elapsedTime = 20;
        DateTime lastReportDateTime = DateTime.Now;

        if (CompareString == null ||
            CompareString == System.String.Empty)
        {
            throw new Exception("CompareString not specified.");
        }
        // Open a new stream.        
        using (System.IO.StreamReader myStream = new System.IO.StreamReader(SourceFile))
        {
            // Process lines while there are lines remaining in the file. 
            while (!myStream.EndOfStream)
            {
                if (worker.CancellationPending)
                {
                    e.Cancel = true;
                    break;
                }
                else
                {
                    line = myStream.ReadLine();
                    WordCount += CountInString(line, CompareString);
                    LinesCounted += 1;

                    // Raise an event so the form can monitor progress. 
                    int compare = DateTime.Compare(
                        DateTime.Now, lastReportDateTime.AddMilliseconds(elapsedTime));
                    if (compare > 0)
                    {
                        state.LinesCounted = LinesCounted;
                        state.WordsMatched = WordCount;
                        worker.ReportProgress(0, state);
                        lastReportDateTime = DateTime.Now;
                    }
                }
                // Uncomment for testing. 
                System.Threading.Thread.Sleep(5);
            }

            // Report the final count values.
            state.LinesCounted = LinesCounted;
            state.WordsMatched = WordCount;
            worker.ReportProgress(0, state);
        }
    }

When I try a similar process (sending a Ping instead of a reading a file) I get this error:

Error: Object reference not set to an instance of an object.
Details: System.Collections.ListDictionaryInternal //This is defined in the MyApp namespace as: using System.Collections
Source: MyApp
StackTrack:    at MyApp.MainForm.Bw01DoWork(Object sender, DoWorkEventArgs e) in
[path]\MainForm.cs:line 152
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)
Target: Void Bw01DoWork(System.Object, System.ComponentModel.DoWorkEventArgs)

Here is my method. Line 152 referenced in the error is the very last line of the last method in MainForm.cs (the var names are different, but you get the idea):

void Bw01DoWork(object sender, DoWorkEventArgs e)
    {
        System.ComponentModel.BackgroundWorker worker;
        worker = (System.ComponentModel.BackgroundWorker)sender;
        PTResults PR = (PTResults)e.Argument;
        PR.SendPings(worker, e);  // Line 152
    }

And the relevant portion of the PTResults.cs class:

using (Ping newPing = new Ping())
        {
            PingReply reply = newPing.Send([Target Site],[Timeout]);
            if(reply.Status == IPStatus.Success)
            {
                state.PingOK = true;
            }
            else if(reply.Status == IPStatus.TimedOut)
            {
                state.PingOK = false;
                state.PingUpdateState = " Timed Out";                   
            }
            else if(reply.Status != IPStatus.Success)
            {
                state.PingOK = false;
                state.PingUpdateState = " FAILED";                          
            }
            else
            {
                state.PingOK = false;
                state.PingUpdateState = " UNKNOWN";                     
            }
            worker.ReportProgress(0, state.PingOK);
        }

I am thinking the System.Net.NetworkInformation.Ping component cannot be invoked the same way System.IO.StreamReader is. Thoughts?

I doubt it makes a difference but FWIW I am coding in SharpDevelop on a Windows 8.1 system.

Answer 1

Take a look at the Ping SendAsync, you may be able to eliminate most of your code - just call PingAsync, and handle the result being sure to dispatch it to the UI thread and then re-queue another call.

http://msdn.microsoft.com/en-us/library/ms144961(v=vs.110).aspx