How to use try catch block in Page.RegisterAsyncTask methods

Question

I have the following code to run some asynchronous call. I am trying to capture the database timeout exception and show some user friendly message.

But putting try, catch block in endInvoke, action does not getting executed. I am using ASP.Net 4.0 & C# 4.0

Page.RegisterAsyncTask(new PageAsyncTask(new BeginEventHandler(beginMyMethod)
      , new EndEventHandler(endMyMethod), new EndEventHandler(timeout => { })
      , true, true));
Page.ExecuteRegisteredAsyncTasks();

Then

IAsyncResult beginMyMethod(object sender, EventArgs e, AsyncCallback cb, object state)
{
        Action r = myMethod;
        return r.BeginInvoke(cb, state);
}


void endMyMethod(IAsyncResult asyncResult)
{
  try{
   myObj.Property // gives object reference error, as it was not set, since DB timeout

  }
  catch(MyTimeoutException ex){
   //it is not getting called
  }
}


private void MyMethod()
{
 try{
   MyObject myObj= //making a database call causes DB time out error
 }
 catch(MyTimeoutException ex){
    //it is getting called
 }
}

How to use try catch block in Page.RegisterAsyncTask methods

Note: I want to prevent object reference error with db time out and async operation

Answer 1

You say that myObj.Property results in a NullReferenceException . Why do you expect to catch it with a catch (MyTimeoutException) , then?

You are using the APM pattern. This requires calling the EndXxx method to get the result of the operation, get any exceptions and potentially release resources. Call the EndXxx method.