將計時器設置爲異步請求

Question

我有通過wsdl生成的函數，其中一個函數是異步函數，它也有一個事件。

ws.GetRequest("Login","Username","Password"); 
ws.GetRequestCompleted+=delegate(object sender,WS.GetRequestCompletedEventArgs e) 
{ 
    //somecode 
} 

我想用於請求創建定時器以上，如果一段時間後不會發生GetRequestCompleted，我將顯示一個錯誤消息。 我無權訪問wsdl函數。

Answer 1

你需要做兩件事情：

當請求開始
• 定時器觸發時，如果回調沒有被稱爲
• 啓動一個定時器，拋出一個異常

它看起來像是發生在一種方法中，並且您使用匿名方法以及委託簽名，所以我建議使用閉包，如下所示：

// Let's say you want to wait for 5 seconds. 
System.Timers.Timer t = new System.Timers.Timer(5000); 

// Has the timer completed? The callback on the web service? 
bool wsCompleted = false, timerCompleted = false, exceptionThrown = false; 

// Need to synchronize access to above, since it will come back on 
// different threads. 
object l = new object(); 

// Set up the callback on the timer. 
t.Elapsed = delegate(object sender, ElapsedEventArgs e) { 
    // Lock access. 
    lock (l) 
    { 
     // Set the flag to true. 
     timerCompleted = true; 

     // If the web service has not completed and 
     // the exception was not thrown, then 
     // throw your exception here. 
     if (!wsCompleted && !exceptionThrown) 
     { 
      // The exception is being thrown. 
      exceptionThrown = true; 
      throw new Exception(); 
     } 
    } 
}; 

// Set up the callback on the web service. 
ws.GetRequestCompleted += 
    delegate(object sender,WS.GetRequestCompletedEventArgs e) { 
     // Dispose of timer when done. 
     using (t) 
     // Lock. 
     lock (l) 
     { 
      // The web service call has completed. 
      wsCompleted = true; 

      // If the timer completed and the exception was 
      // not thrown, then do so here. 
      if (timerCompleted && !exceptionThrown) 
      { 
       // The exception is being thrown. 
       exceptionThrown = true; 
       throw new Exception(); 
      } 
     } 

     // Handle callback. 
    }; 

// Start the timer, make the web service call. 
t.Start(); 
ws.GetRequest("Login","Username","Password"); 

需要注意以下幾點：

• 你必須在這兩個計時器回調和Web服務的回調，以檢查其他條件有不得到滿足，如果該異常有不被拋出。你不想拋出異常兩次。
• 您沒有指出如何獲取例外回給用戶。現在，這個異常將在除調用線程之外的其他線程上拋出。這將導致用戶非常難看的例外。
• 的Timer實例的處理在回調Web服務處理。這假設web服務的回調將總是完成，是否成功。