How to handle Task.Run Exception

Question

I had a problem with catching the exception from Task.Run which was resolved by changing the code as follows. I'd like to know the difference between handling exceptions in these two ways :

In the Outside method I can't catch the exception, but in the Inside method I can.

void Outside()
{
    try
    {
        Task.Run(() =>
        {
            int z = 0;
            int x = 1 / z;
        });
    }
    catch (Exception exception)
    {
        MessageBox.Show("Outside : " + exception.Message);
    }
}

void Inside()
{
    Task.Run(() =>
    {
        try
        {
            int z = 0;
            int x = 1 / z;
        }
        catch (Exception exception)
        {
            MessageBox.Show("Inside : "+exception.Message);
        }
    });
}

Answer 1

The idea of using Task.Wait will do the trick but will cause the calling thread to (as the code says) wait and therefore block until the task has finalized, which effectively makes the code synchronous instead of async.

Instead use the Task.ContinueWith option to achieve results:

Task.Run(() =>
{
   //do some work
}).ContinueWith((t) =>
{
   if (t.IsFaulted) throw t.Exception;
   if (t.IsCompleted) //optionally do some work);
});

If the task needs to continue on the UI thread, use the TaskScheduler.FromCurrentSynchronizationContext() option as parameter on continue with like so:

).ContinueWith((t) =>
{
    if (t.IsFaulted) throw t.Exception;
    if (t.IsCompleted) //optionally do some work);
}, TaskScheduler.FromCurrentSynchronizationContext());

This code will simply rethrow the aggregate exception from the task level. Off course you can also introduce some other form of exception handling here.