TPL Exception handling - c#-4.0

Question

http://msdn.microsoft.com/en-us/library/dd997415.aspx
Per the article referenced above I am trying to handle exceptions in a continuatin task. The example I am citing in the above article is this:
var task1 = Task.Factory.StartNew(() =>
{
throw new MyCustomException("Task1 faulted.");
})
.ContinueWith((t) =>
{
Console.WriteLine("I have observed a {0}",
t.Exception.InnerException.GetType().Name);
},
TaskContinuationOptions.OnlyOnFaulted);
My code is:
Task<string> task = Task<string>.Factory.StartNew(() => process.StartTask(this));
task.ContinueWith(CloseDialog, TaskContinuationOptions.OnlyOnFaulted);
In StartTask, I throw an error just like the example. My expectation is that CloseDialog will execute and I can examine task.Exception within that method as shown by the example. However when I throw the exception I the code simply stops with an unhandled exception. Should I be using a try/catch block? If so, where?
By the way, I want my continuation task (CloseDialog) to ALWAYS run. I'm just using .OnlyOnFaulted because that is what is shown in the example.

Answer 1

A continuation can find out if an exception was thrown by the antecedent Task by the antecedent task's exception property. The following prints the results of a NullReferenceException to the console
Task task1 = Task.Factory.StartNew (() => { throw null; });
Task task2 = task1.ContinueWith (ant => Console.Write(ant.Exception());
If task1 throws an exception and this exception is not captured/queried by the continuation it is considered unhandled and the application dies. With continuations it is enough to establish the result of the task via the Status keyword
asyncTask.ContinueWith(task =>
{
// Check task status.
switch (task.Status)
{
// Handle any exceptions to prevent UnobservedTaskException.
case TaskStatus.RanToCompletion:
if (asyncTask.Result)
{
// Do stuff...
}
break;
case TaskStatus.Faulted:
if (task.Exception != null)
mainForm.progressRightLabelText = task.Exception.InnerException.Message;
else
mainForm.progressRightLabelText = "Operation failed!";
default:
break;
}
}
If you don't use continuations you either have to wait on the task in a try/catch block or query a task's Result in a try/catch block
int x = 0;
Task<int> task = Task.Factory.StartNew (() => 7 / x);
try
{
task.Wait();
// OR.
int result = task.Result;
}
catch (AggregateException aggEx)
{
Console.WriteLine(aggEx.InnerException.Message);
}
Hope this help even if it is a bit late and you know all there is by now! :]