Retrieve FormatException Argument

Question

I'm using a closed-source third-party library like this:

object val = SomeClass.ExtractValue( someObject );

Now somewhere further down the road, the third-party library tries to parse a DateTime value that has an unexpected format and throws a FormatException.

In this case, I would like to retrieve the string that it hasn't succeeded to parse and try to parse it myself. Something like this:

object val;
try
{
    val = SomeClass.ExtractValue( someObject );
}
catch( FormatException e )
{
    string failed = e.GetParseArgument( );
    val = DateTime.Parse( failed + " 2010" );
}

Yes, simply appending the year is pretty pointless, but you get the idea. The third-party library doesn't support all formats I need, but I can't easily get the data from "someObject" either. (Yes, I could try to replicate what the library does using Reflector, but I'd like to avoid that.)

Is there any way to do this? Thanks.

Do you have control over the input to the 3rd party library? IE, could you parse the dateTime in SomeObject, and re-save it in a format you know the 3rd party can accept before passing it in? — Andrew M, Dec 09 '10 at 18:16

score 0 · Answer 1 · answered Dec 09 '10 at 18:52

Since someObject is an IDataReader, you could create a decorator and pass that into ExtractValue. You could then intercept the date string and modify the format before it gets passed to the library e.g.

public class DateFormattingDataReader : IDataReader
{
    private readonly IDataReader inner;

    public DateFormattingDataReader(IDataReader inner)
    {
        this.inner = inner;
    }

    public string GetString(int index)
    {
        string s = this.inner.GetString(index);
        if(index == problematicColumnIndex)
        {
            //try to parse string and then format it for the library
        }
        else return s;
    }
}

Alternatively you could record all values read from the reader, then you can get the failing data as the last read item and try to parse it yourself.

Thanks, it's not quite as simple a solution as I'd hoped, but I'll give it a shot. — Andreas, Dec 10 '10 at 16:23
@Andreas - Since IDataReader is quite a large interface it may be easier to use a dynamic proxy like linfu and intercept the required method instead of creating your own custom decorator class. — Lee, Dec 10 '10 at 18:53

Retrieve FormatException Argument

1 Answers1