wrapping a dataview in a using statement produces bizarre results. Am I misusing the using?

Question

This problem really baffeled me today. I'm working in Visual studio 2012, C# .net 4 app (Not sure if it matters).

I have some datatables that have multiple results in them. To figure out the best one to pick I'm looking for the one with the best Jaro-Winkler score, and sending that one back.
I sort the table results by making a dataview and in an attempt to properly dispose my data elements, I've wrapped the dataview in a using statment. The code looks like this:

 public static DataRow getBestCandidate(DataTable searchTable, string searchName)
        {
            if (searchTable.Rows.Count == 1) //Nothing to do if there's only one row
            {
                return searchTable.Rows[0];
            }        

           int tableSize = searchTable.Rows.Count;
                for (int i = 0; i < tableSize; i++)
                {
                        //Iterate through each entry and record the Jaro distance between our original search term.
                        searchTable.Rows[i][7] = jaro.getScrubbedDistance(searchTable.Rows[i][1].ToString(), searchName);
                }

                using (DataView dv = searchTable.DefaultView) //Sort the results
                {
                    dv.Sort = "JaroDistance desc";                 
                    return dv[0].Row; //Send back the result with the highest Jaro score.
                }          
        }

Here's what's weird. The first time I call this, it works just fine. Exactly as I want it to. If I call it twice in a row from the same method, it almost works the second time. When running a trace it gets all the way to the line "return dv[0].Row; " and when it goes to execute that, the object DV is null. It behaves exactly like the object was disposed of before I was done with it. This ends up killing that thread with an exception.

I took out the using statement and replaced it with this:

 DataView dv = searchTable.DefaultView;
                    dv.Sort = "JaroDistance desc";

                    return dv[0].Row;

Then it works just fine. Hammering the methods didn't seem to cause huge memory spikes.

Is the using wrapper even needed? Why is it becoming null right before I return it?

Answer 1

Assuming the searchTable is the same instance, you are disposing of its DefaultView, an object you are sharing each time you call the method.

The using isn't necessary here, but rather around searchTable in whatever parent method manages that object.