Question

我想调用一个每隔几秒返回一个值的方法。我尝试使用Timer和elapsedEventandler，但在这种情况下，方法的返回类型无效。我使用TimerTask类在Java中执行相同的任务。

我希望它在.NET 2.0中，因为我正在使用Visual Studio 2005。

以下是我遇到问题的程序。我尝试使用匿名方法，但在这种情况下response的值在匿名方法之外不存在：

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;
}

如何在response方法中获取Run的值并将其发送给Run方法的来电者？

Answer 1

您可以让您的调用者为该类提供一个回调委托的计时器以传回该值。

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);
    }
}

更新：如果您希望来电者（OtherClass）能够取消定时器，则只需将Action<string>更改为Func<string, bool>即可并让调用者（OtherClass）返回一个关于是否停止计时器的bool ......

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);
    }
}

Answer 2

创建一个Thread并让线程调用你想要的方法，并给线程一个休眠时间5秒钟：

Thread loopThread = new Thread(new ThreadStart(this.MainLoop));
loopThread.Start();

private void MainLoop()
{
     while(true)
     {
         // Do stuff
         Thread.Sleep(5000);
     }
}

调用一个每5秒返回一个值的方法

2 个答案: