AggregateException C# example

Question

I have seen an example of AggregateException on the web and I'm trying to figure out how it works. I have written a simple example, but my code for some reason doesn't work.

Could someone explain to me what the problem is?

public static void Main()
{
    try
    {
        Parallel.For(0, 500000, i =>
        {
            if (i == 10523)
                throw new TimeoutException("i = 10523");
            Console.WriteLine(i + "\n");
        });
    }
    catch (AggregateException exception)
    {
        foreach (Exception ex in exception.InnerExceptions)
        {
            Console.WriteLine(ex.ToString());
        }
    }
}

Answer 1

You need to call Handle on the inner exceptions. From MSDN's documentation on Handle:

Each invocation of the predicate returns true or false to indicate whether the Exception was handled. After all invocations, if any exceptions went unhandled, all unhandled exceptions will be put into a new AggregateException which will be thrown. Otherwise, the Handle method simply returns. If any invocations of the predicate throws an exception, it will halt the processing of any more exceptions and immediately propagate the thrown exception as-is.

The example code, also from MSDN:

public static void Main()
{
    var task1 = Task.Run(() => { throw new CustomException("This exception is expected!"); });

    try 
    {
        task1.Wait();
    }
    catch (AggregateException ae)
    {
        // Call the Handle method to handle the custom exception,
        // otherwise rethrow the exception.
        ae.Handle(ex => 
        { 
            if (ex is CustomException)
                Console.WriteLine(ex.Message);
            return ex is CustomException;
        });
    }
}