C# Windows Service Events

问题

So I am just messing around here nothing production just proof of concept with my first ever Windows Service.

I am trying to essentially create a windows service that sits as the listener for a signalr connection. In essence, I will have a windows application and a windows service. The win service will handle connecting to the signalr hub and on signalr calls fire an event. The windows application will listen for these events and perform actions based on them.

Currently I cannot get this to work. I have never worked with events, or windows services before. In my windows application my events never hit their break points, as well I log an error of null reference exception from the

ConnectToHub()

Alright if I comment out the OnConnected() method call I log a successful connection to the hub. I have never worked with events before so is my mistake with the events?

I debated that this approach was a bit overkill. However, for me it was a proof of concept that I could find a use for a long running windows service, and adding some events into the mix.

Code for service:

public delegate void MessageRecievedEventHanlder(object sender, MessageRecievedArgs e);
public delegate void ConnectedToHubEventHandler(object sender, ConnectedArgs e);
public partial class SignalRService : ServiceBase
{

    IHubProxy _hub;
    HubConnection connection;
    string url = @"http://localhost:8080/";
    private Message LastMessage;
    public static event MessageRecievedEventHanlder NewMessage;

    protected virtual void OnNewMessage(MessageRecievedArgs e)
    {
        NewMessage(null, e);
    }

    public static event ConnectedToHubEventHandler Connected;

    protected virtual void OnConnected(ConnectedArgs e) {
        System.IO.File.WriteAllText(@"C:\Users\Bailey Miller\Desktop\FTP\Logg.txt", "Hit OnConnected " + e.Success +" " + Connected != null ? "Isn't null" : "Null event");
        Connected(null, e);

    }

    public SignalRService()
    {
        InitializeComponent();
    }

    protected override void OnStart(string[] args)
    {
        ConnectToHub().Wait();

    }

    private async Task ConnectToHub()
    {
        try
        {
            //Connecting

            if (connection == null)
            {
                connection = new HubConnection(url);
            }
            if (_hub == null)
            {
                _hub = connection.CreateHubProxy("ChatHub");
            }

            await connection.Start();

            //Connected

            //Configure all the incoming options
            _hub.On<Message>("RecieveMessage", IncomingMessage);
            System.IO.File.WriteAllText(@"C:\Users\Bailey Miller\Desktop\FTP\Succes.txt", "Connected");
            OnConnected(new ConnectedArgs(true));

        }
        catch (Exception ex)
        {
            //Failed
            //OnConnected(new ConnectedArgs(false));
            System.IO.File.WriteAllText(@"C:\Users\Bailey Miller\Desktop\FTP\Fail.txt", "Failed to connect " + ex.Message.ToString());
        }

    }

    private void IncomingMessage(Message state)
    {
        DateTime? lmt;
        //Determine if has lastmessagetime
        if (LastMessage == null) {
            lmt = null;
        }
        else {
            lmt = LastMessage.RecievedAt;
        }

        LastMessage = state;

        //New Message
        //OnNewMessage(new MessageRecievedArgs(state, lmt));
    }

    protected override void OnStop()
    {
    }
}

public class MessageRecievedArgs : EventArgs
{
    public Message NewMessage { get; }
    public DateTime? LastMessageTime { get; }

    public MessageRecievedArgs(Message msg, DateTime? lmt) {
        this.NewMessage = msg;
        this.LastMessageTime = lmt;
    }
}

public class ConnectedArgs : EventArgs {
    public bool Success { get; }

    public ConnectedArgs(bool suc) {
        this.Success = suc;
    }
}

My windows application as of now:

public MainWindow()
    {
        InitializeComponent();
        SignalRService.SignalRService.NewMessage += SignalRService_NewMessage;
        SignalRService.SignalRService.Connected += SignalRService_Connected;
    }

    private void SignalRService_Connected(object sender, SignalRService.ConnectedArgs e)
    {
        throw new NotImplementedException();
    }

    private void SignalRService_NewMessage(object sender, SignalRService.MessageRecievedArgs e)
    {
        throw new NotImplementedException();
    }

回答1:

Your question is a bit broad- you don't describe exactly what isn't working, so I am guessing that when you start your service, it says "starting..." for a long while and eventually windows service manager gives you an error saying your service didn't start in a timely fashion. The issue is that OnStart() is expected to return- you can't block the thread there with the Wait() call. My suggestion would be to spawn a new background thread here to perform the waiting, then exit. That should get you past the first hurdle.

As another aside... You can add a regular main method to a windows service project, change the project type to Console Application, and run it that way to reduce your debugging cycle time. Then when you are sure it basically works, change the project type back to Windows Service and install it.

EDIT: Now that you have a better error description, I see the real problem. The issue is that you are raising an event without checking for null first. Event fields are null until you attach a listener. So change your code as follows:

protected virtual void OnConnected(ConnectedArgs e) {
    System.IO.File.WriteAllText(@"C:\Users\Bailey Miller\Desktop\FTP\Logg.txt", "Hit OnConnected " + e.Success +" " + Connected != null ? "Isn't null" : "Null event");

    ConnectedToHubEventHandler connectedEvent = Connected;
    if (connectedEvent != null) // This event might be null, so check first
        connectedEvent(null, e);

}

来源：https://stackoverflow.com/questions/44274894/c-sharp-windows-service-events

标签

windows

events

signalr