使用 C# 监听文本/事件流

Question

I am writing a C# class to wrap around a simple web service. The RESTful stuff was easy to wrap up, but now I need to raise an event when something on the server changes.

I've set the server up to make an event stream available, but I don't know how to pick up the stream in C#.

Currently I'm dong something like this:

public class ServiceWrapper
{
    private readonly wc = new WebClient();

    public ServiceWrapper()
    {
        wc.OpenReadAsync(new Uri(UriOfEvent));
        wc.OpenReadCompleted += ServerEventOccurs;
    }

    private void ServerEventOccurs(object sender, OpenReadCompletedEventArgs args)
    {
        using (var sr = new StreamReader(args.Result))
        {
            var message = ParseStream(sr);
            RaiseServerEventOccurred(message);
        }

        wc.OpenReadAsync(new Uri(UriOfEvent));
    } 

    //usual code for declaring and raising ServerEventOccurred event
}

In my test the event gets picked up once, but not twice. The event on the server is essentially a switch - something happens and it goes on, something else happens and it goes off. I know the switching works, because I've hooked the event stream up to a normal web page to test it.

How should I be dealing with event streams in C#?

Edit 1: I've updated the code to fix the bug TimVK points out, but the event stream still isn't being picked up the second time it should be.

Answer 1

Doesn't it work when you put your wc as a property in the class instead of creating always a new one in your methods?

public class ServiceWrapper 
{ 
    WebClient wc {get;set;}
    public ServiceWrapper() 
    { 
        wc = new WebClient(); 
        wc.OpenReadAsync(new Uri(UriOfEvent)); 
        wc.OpenReadCompleted += ServerEventOccurs; 
    } 
 
    private void ServerEventOccurs(object sender, OpenReadCompletedEventArgs args) 
    { 
        using (var sr = new StreamReader(args.Result)) 
        { 
            var message = ParseStream(sr); 
            RaiseServerEventOccurred(message); 
        } 
 
        wc = new WebClient(); 
        wc.OpenReadAsync(new Uri(UriOfEvent)); 
    }  
 
    //usual code for declaring and raising ServerEventOccurred event 
} 

Then I suppose the event should be raised everytime.

Answer 2

namespace WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        WebClient myWebRequest = null;
        String Path = "http://192.168.196.106/home/events/";
        Uri uri = null;

        public Form1()
        {
            InitializeComponent();

            uri = new Uri(Path);

            this.myWebRequest = new WebClient();
            this.myWebRequest.Headers.Set("Host", "192.168.196.106");

            this.myWebRequest.OpenReadCompleted += MyWebRequest_OpenReadCompleted;
        }

        private async void MyWebRequest_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
        {
            using (var sr = new StreamReader(e.Result))
            {
                try
                {
                    while (true)
                    {
                        var message = await sr.ReadLineAsync();
                        Debug.WriteLine("message = {0}", (object)message);
                    }
                }
                catch (WebException ex)
                {
                    Debug.WriteLine("WebException: {0}", (object)ex.Message);
                }
                catch (IOException ex)
                {
                    Debug.WriteLine("IOException: {0}", (object)ex.Message);
                }
                catch (Exception ex)
                {
                    Debug.WriteLine("Exception: {0}", (object)ex.Message);
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            myWebRequest.OpenReadAsync(uri);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            myWebRequest.CancelAsync();
        }
    }