Question

I want to call a method which returns a value every few seconds.
I have tried using a Timer with elapsedEventandler, but the return type of the method is void in this case. I have used the TimerTask class to perform the same task in Java.

I want it to be in .NET 2.0 as I’m using Visual Studio 2005.

Below is the program I’m having trouble with. I tried to use an anonymous method, but the value of response in this case does not exist outside the anonymous method:

public static string Run(string address)
{                     
    string response = "A";
    Timer t = new Timer();
    t.Elapsed += delegate 
    {                         
        response = callURL(address);
        console.writeln(response);
        // The actual response value is printed here                
    };          
    t.Interval = 3000;
    t.Start();                      
    Console.WriteLine("response string is " + response);
    // response string is A

    return response;
}

public static string callURL(string address)
{
    className sig = new ClassName(); 
    String responseBody = sig.getURL(address);

    return responseBody;
}

How do I get the value of response in the Run method and send it to the caller of the Run method?

Answer 1

You could have your caller give the class with the timer a callback delegate to pass back the value.

public class YourClass
{
    public static void Run(string address, Action<string> callback)
    {                     
        Timer t = new Timer();
        t.Elapsed += delegate {                         
            var response = callURL(address);

            callback(response);
        };          
        t.Interval = 3000;
        t.Start();
    }
}

public class OtherClass
{
    public void ProcessResponse(string response)
    {
         // do whatever you want here to handle the response...
         // you can write it out, store in a queue, put in a member, etc.
    }

    public void StartItUp()
    {
         YourClass.Run("http://wwww.somewhere.net", ProcessResponse);
    }
}

UPDATE: If you want the caller (OtherClass) to be able to cancel the timer, you could simply change from an Action<string> to a Func<string, bool> and have the caller (OtherClass) return a bool on whether to stop the timer or not…

public class YourClass
{
    public static void Run(string address, Func<string, bool> callback)
    {                     
        Timer t = new Timer();
        t.Elapsed += delegate {                         
            var response = callURL(address);

            // if callback returns false, cancel timer
            if(!callback(response))
            {
                t.Stop();
            }
        };          
        t.Interval = 3000;
        t.Start();
    }
}

public class OtherClass
{
    public bool ProcessResponse(string response)
    {
         // do whatever you want here to handle the response...
         // you can write it out, store in a queue, put in a member, etc.
         // check result to see if it's a certain value...
         // if it should keep going, return true, otherwise return false
    }

    public void StartItUp()
    {
         YourClass.Run("http://wwww.somewhere.net", ProcessResponse);
    }
}