Object Disposes Before Using Datas

Question

I'm struggling with some System.Data.SqlClient.SqlDataReader problems.

Actually, I made a DatabaseHandler for execute queries more convenient, with IDisposable interface for using statements.

When I use the handler for reading single article, query successfully executed, however, the handler disposed before I use data.

Then, the result is NullReferenceException. Here's the article reading code, and Dispose().

// Article Reading Code
using (var ArticleHandler = new DatabaseHandler())
{
    var ArticleReader = ArticleHandler.ExecuteCommand("ARTICLE_INQUIRY",
        DatabaseHandler.QueryType.ExecuteReader,
        new DatabaseParameter[]
        {
            new DatabaseParameter("seq", Sequence)
        }) as System.Data.SqlClient.SqlDataReader; //Query Successful

    if (!ArticleReader.HasRows)
    {
        Response.Redirect("/articles/list.aspx");
    }
    else
    {
        ArticleReader.Read(); //Data Read Successful

        CurrentArticle.title = (string)ArticleReader["title"]; //NullReferenceException ?
        CurrentArticle.category = (string)ArticleReader["category"];
        CurrentArticle.datetime = (string)ArticleReader["written_datetime"];
        CurrentArticle.content = (string)ArticleReader["content"];
    }
}


/* Database Handler Dispose() */
public void Dispose()
{
    CurrentConnection = null;
}

P.S. I checked column names, and they are match with database information.

So `CurrentArticle` is null? - can't diagnose that with the code provided. Unrelated but If CurrentConnection is an SqlConnection you need to dispose it in your dispose() not just set it to null. — Alex K., Nov 22 '16 at 13:42
Well, **DatabaseHandler** class stores connections to `private SqlConnection CurrentConnection;`, so I thought it need to be nulled. — Kangjun Heo, Nov 22 '16 at 13:42
I think the **ArticleReader** is disposed before I use datas. — Kangjun Heo, Nov 22 '16 at 13:43
No, `ArticleReader` is likely fine else `.Read()` would fail. `CurrentArticle` is the culprit, test and see. — Alex K., Nov 22 '16 at 13:44
I declared `CurrentArticle` on current class as `protected Article CurrentArticle;`. — Kangjun Heo, Nov 22 '16 at 13:45
`Article` is class for storing informations from `ArticleReader`. — Kangjun Heo, Nov 22 '16 at 13:46
If your `CurrentConnection` is a SqlConnection, then setting it to null is not enough to correctly dispose of it. You should call it's `Dispose()` method first. — Hans Keﬆing, Nov 22 '16 at 13:51
`protected Article CurrentArticle` - after this `CurrentArticle` is still `null` in the absence of a `new`. — Alex K., Nov 22 '16 at 13:57
Ah, I forgot to initialize `CurrentArticle` with `new`.... sorry ;( — Kangjun Heo, Nov 22 '16 at 14:00

score 0 · Accepted Answer · answered Nov 22 '16 at 13:53

0

Check inside your database handler if you are closing the underlying sqlconnection before accessing the reader to access data in the next line. If the sqlconnection is getting closed, the reader will get closes automatically. Paste the handler Execute command code so we can have look at it

answered Nov 22 '16 at 13:53

Swetha

457
4
7

well, I used the handler several times, but problem occured just here. I just solved the problem. thank you for answer anyway! – Kangjun Heo Nov 22 '16 at 14:01
What was the issue? – Swetha Nov 22 '16 at 14:29
NullReferenceException thrown when I access `CurrentArticle`. I misunderstood that `Dispose()`occured such issues because of debugger's flow. – Kangjun Heo Nov 22 '16 at 14:33

Object Disposes Before Using Datas

1 Answers1