是否有可能隱藏回調機制在一個單一的方法？

Question

我有一個這樣的接口：

interface IAuthentication 
{ 
    void AuthenticateAsync(string user, string pwhash); 
    event EventHandler<AuthenticationResult> AuthenticationDone; 
} 

這是通過在完成時引發事件。現在，我想它完成後包裹返回認證結果單，阻斷方法在這裏面的機制：

AuthenticationResult Authenticate(string user, string pwhash) 
{ 
    var auth = GetIAuthenticator(); 
    // ... do something 
    return <the authentication result from the even argument>; 
} 

這可能不知？

Answer 1

隨着等待句柄，你並不需要檢查一些標誌，塊線程和設定的超時：

private AuthenticationResult Authenticate(string user, string pwhash) 
{    
    IAuthentication auth = GetIAuthenticator(); 
    AuthenticationResult result = null; 
    AutoResetEvent waitHangle = new AutoResetEvent(false); 

    auth.AuthenticationDone += (o, e) => 
     { 
      result = e; 
      waitHangle.Set(); 
     }; 

    auth.AuthenticateAsync(user, pwhash); 
    waitHangle.WaitOne(); // or waitHangle.WaitOne(interval); 
    return result; 
} 

Answer 2

private AuthenticationResult Authenticate(string user, string pwhash) 
{ 
    bool isDone = false; 
    AuthenticationResult results = null 
    var auth = GetIAuthenticator(); 
    auth.AuthenticationDone += (o, e) => 
    { 
     isDone = true; 
     results = e; 
    }; 

    auth.AuthenticateAsync(user, pwhash); 

    long maxWaitTimeSeconds = 10; 
    long thresholdMilliseconds = 100; 
    int countToWait = maxWaitTimeSeconds * 1000/thresholdMilliseconds; 
    while (!isDone || countToWait-- > 0) 
    { 
     Thread.Sleep(thresholdMilliseconds); 
    } 

    if (countToWait == 0 && !isDone) 
    { 
     // TODO: timeout handling 
    } 

    return results;  
} 

PS： 如果事件參數永遠不能爲null - 你可以擺脫isDone可變的，只是使用result != null爲「完成認證」指標

Answer 3

當你使用.NET 4.0，你可以利用任務並行庫。

這裏是一個非常基本的程序，說明如何使用TaskCompletionSource：

public class Test 
{ 
    public void Go() 
    { 
     ThreadPool.QueueUserWorkItem((z) => this.Imp()); 
    } 

    private void Imp() 
    { 
     Console.WriteLine("Asynchronous operation in progress (1/2)..."); 
     Thread.Sleep(2000); 
     Console.WriteLine("Asynchronous operation in progress (2/2)..."); 

     if (this.Done != null) 
     { 
      this.Done(this, EventArgs.Empty); 
     } 
    } 

    public event EventHandler Done; 
} 

internal class Program 
{ 
    private static void Main(string[] args) 
    { 
     Test test = new Test(); 

     TaskCompletionSource<object> tcs = new TaskCompletionSource<object>(null); 

     Console.WriteLine("Starting asynchronous operation"); 

     Task.Factory.StartNew(() => 
     { 
      test.Done += (sender, e) => tcs.SetResult(null); 
      test.Go(); 
     }); 

     // Blocking until completion of the async operation 
     var tmp = tcs.Task.Result; 

     Console.WriteLine("Asynchronous operation completed"); 

     Console.ReadKey(); 
    } 
} 

結果是：

Starting asynchronous operation 
Asynchronous operation in progress (1/2)... 
Asynchronous operation in progress (2/2)... 
Asynchronous operation completed 

正如你所看到的，執行流程被阻塞，直到異步操作終止。