Question

I’m having a problem getting TryParse to work correctly for me. I have a list of values that I am almost assured are valid (as they come from another component in our system) but I would like to make sure there is proper error handling in place.

Here is an example list of my values:

20.00
20.00
-150.00

And here is the method I originally wrote:

 private decimal CalculateValue(IEnumerable<XElement> summaryValues)
        {
            decimal totalValue = 0;

            foreach (XElement xElement in summaryValues)
            {
                decimal successful;
                Decimal.TryParse(xElement.Value, out successful);
                if (successful > 0)
                    totalValue += Decimal.Parse(xElement.Value);
            }
            return totalValue;
        }

The variable ‘successful’ was returning false for -150.00, so I added NumberStyles:

private decimal CalculateValue(IEnumerable<XElement> summaryValues)
        {
            decimal totalValue = 0;

            foreach (XElement xElement in summaryValues)
            {
                decimal successful;
                Decimal.TryParse(xElement.Value, NumberStyles.AllowLeadingSign, null, out successful);
                if (successful > 0)
                    totalValue += Decimal.Parse(xElement.Value, NumberStyles.AllowLeadingSign);
            }
            return totalValue;
        }

However, now that I have the NumberStyles in there, none of the numbers will parse! I feel good about having IFormatProvider set to null as this is all within our system. Does anyone see what I may be doing wrong?

Answer 1

The other answers have got the right idea with regard to the proper way to use Decimal.TryParse. However, if I were writing the method in question, I’d use LINQ to work with LINQ-to-XML objects:

private decimal CalculateValue(IEnumerable<XElement> summaryValues)
{
    return summaryValues
        .Sum(el =>
             {
                 decimal value;
                 if (Decimal.TryParse(el.Value, out value))
                     return value;
                 return 0M;
             });
}

This version works the exact same way, but it uses the Enumerable.Sum method to calculate the total. All I have to supply is an inline function that extracts decimal values from an XElement.