Using events to trigger ActionResult in ASP.NET MVC - asp.net-mvc

Question

I am working on an ASP.NET MVC web service. In a web page, when a user clicks on a button, this triggers a complex method that takes a bit of time to finish. I want to redirect the user to a waiting page and then, when the process is finished, to redirect the user to a new page.
When the process is done it raises an event, which I can listen to from the controller. But I cannot make the last step to work (the controller redirecting to the new page upon receiving the event).
Here is my very naïve attempt at doing it (with simpler names):
public MyController()
{
EventsControllerClass.ProcessComplete += new EventHandler<MyArgsClass>(OnEventReceived);
}
private void OnEventReceived(object sender, MyArgsClass eventArguments)
{
RedirectToPage();
}
private ActionResult RedirectToPage()
{
return RedirectToAction("PageName");
}

Answer 1

After many days working on this, I have a viable solution. It may not be pretty, but it works, and maybe some ideas can be useful for other people, so here it goes:
I will explain the solution to my particular problem: I need a button to redirect to a "waiting" page while a longer process runs in the background and raises an event when it is finished. When this event is received, we want to redirect the user (automatically) to a final page.
First, I created a class to listen to the event. I tried doing this directly in the controller, but you need to be careful about signing and unsigning, because apparently controllers get created and destroyed at each request. In this "listener class" I have a bool property that is set to "true" when the event is received.
When the first action is triggered, the controller normally redirects to the "wait" page, where I have this simple java script redirecting to the new action:
<script type="text/javascript">
window.location = "#Url.Action("WaitThenRedirect", "AuxiliaryControllerName")";
</script>
This sets in motion the long process (through another event). The key is that I do this with an asynchronous action (this controller inherits from AsyncController). (Note I used an auxiliary controller. This is to keep all asynchronous stuff apart.) This is how this looks (more info here):
public static event EventHandler<AuxiliaryEventsArgs> ProcessReady;
public void WaitThenRedirectAsync()
{
AsyncManager.OutstandingOperations.Increment();
ProcessReady += (sender, e) =>
{
AsyncManager.Parameters["success"] = e.success;
AsyncManager.OutstandingOperations.Decrement();
};
WaitForEvent();
}
public ActionResult WaitThenRedirectCompleted(bool success)
{
if (success)
{
return RedirectToAction("RedirectToView", "ControllerName");
}
else
{
return RedirectToAction("UnexpectedError", "ControllerName");
}
}
private void WaitForEvent()
{
bool isWaitSuccessful = true;
int waitingLoops = 0;
int waitingThreshold = 200;
int sleepPeriod = 100; // (milliseconds)
while (!EventsListener.IsTheThingReady())
{
System.Threading.Thread.Sleep(sleepPeriod);
++waitingLoops;
if (waitingLoops > waitingThreshold)
{
System.Diagnostics.Debug.WriteLine("Waiting timed out!");
isWaitSuccessful = false;
break;
}
}
isWaitSuccessful = true;
if (null != ProcessReady)
{
AuxiliaryEventsArgs arguments = new AuxiliaryEventsArgs();
arguments.success = isWaitSuccessful;
try
{
ProcessReady(null, arguments);
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine("Error in event ProcessReady" + ex);
}
}
}
I believe it is possible to use ajax syntax for alternative solutions, but this is what I have and it works nicely. I believe this is not a very common need, but hopefully someone will benefit!