c# - Is there a way to handle exceptions thrown by a task without the task freezing the UI?

Question

public async void CallTask()
{
    try
    {
        await Task.Run(MyTaskMethod);
    }
    catch (ArgumentException ex) // Exception doesn't get handled
    {
        MessageBox.Show(ex.Message);
    }
}

public Task MyTaskMethod()
{
    throw new ArgumentException("This is an error message"); 
}

My task throws an exception I want to capture in a higher level.

How can I handle the exception being thrown on MyTaskMethod without freezing the UI ?

Answer 1

Two options:

1. Catch the exception in MyTaskMethod
2. Catch AggregateException that is thrown by the Task

I believe 1 is fairly straight forwards to understand.

Number 2 looks like this:

public async void CallTask()
{
    try
    {
        await Task.Run(MyTaskMethod);
    }
    catch (AggregateException ex) // Exception doesn't get handled
    {
        MessageBox.Show(ex.InnerExceptions[0].Message);
    }
}

public Task MyTaskMethod()
{
    throw new ArgumentException("This is an error message"); 
}

This is necessary because when an exception is thrown on a Task it gets wrapped in an AggregateException before being returned. This means trying to catch the inner exception will fail, so we need to first catch the AggregateException and then unwrap.