try catch skipping exception

Question

try
{
    return strngarray.Select(strngarrayelem =>
    {
        string[] data = strngarrayelem .Split(',');

        return new xyzClass(data[1], data[2], data[0], (Color)System.Windows.Media.ColorConverter.ConvertFromString(data[3]), data.Length > 4 ? data[4] : "N/A");
    });
}
catch (Exception ex)
{
    MessageBox.Show("abc");
    return Enumerable.Empty<xyzClass>();
}

I am getting format exception in

(Color)System.Windows.Media.ColorConverter.ConvertFromString(data[3])

I try catching it by try-catch but exception is still thrown by app level try catch and not caught by my local try catch. Why my try catch not getting error ?

Answer 1

You are just returning a LINQ query, it's not yet executed(like for example with ToList).

So if you want to catch the exception here you should consider materializing it to a collection in this method. You could still return IEnumerable<xyzClass> since List<xyzClass> implements that interface.

try
{
    return strngarray.Select(strngarrayelem =>
    {
        string[] data = strngarrayelem .Split(',');

        return new xyzClass(data[1], data[2], data[0], (Color)System.Windows.Media.ColorConverter.ConvertFromString(data[3]), data.Length > 4 ? data[4] : "N/A");
    }).ToList(); // <------- HERE !!!
}
catch (Exception ex)
{
    MessageBox.Show("abc");
    return Enumerable.Empty<xyzClass>();
}

If you don't know which method is just returning a query, look at the documentation in MSDN for the keyword deferred. For example Enumerable.Select:

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach

Methods like for example Enumerable.ToList or ToArray call GetEnumerator, so they will execute the query. MSDN:

The ToList<TSource>(IEnumerable<TSource>) method forces immediate query evaluation and returns a List<T> that contains the query results. You can append this method to your query in order to obtain a cached copy of the query results.

ToArray<TSource> has similar behavior but returns an array instead of a List<T>.