visual studio 2012 c# catch exception error

Question

My c# coding in Master page is the following

DBLayer odb = new DBLayer();

SqlDataReader dr;

DataSet ds = new DataSet();

protected void Page_Load(object sender, EventArgs e)
{
    if (DropDownList1.SelectedItem.ToString() == "Commercial")
    {

        bind1();
    }
    else if (DropDownList1.SelectedItem.ToString() == "Residential")
    {
        bind2();
    }
    else
    {
        bind3();
    }
}
public void bind1()
{
    string query = "select * from commercialproperty";
    dr = odb.SelectMethod(query);
    if (dr.Read())
    {
        Label11.Text = dr[0].ToString();
        Label1.Text = dr[1].ToString();
        Label2.Text = dr[2].ToString();
        Label3.Text = dr[3].ToString();
        Label4.Text = dr[4].ToString();
        Label5.Text = dr[5].ToString();
        Label6.Text = dr[6].ToString();
        Label7.Text = dr[7].ToString();
        Label8.Text = dr[8].ToString();
        Label9.Text = dr[9].ToString();
        Label10.Text = dr[10].ToString();
    }
    else
    {
        Response.Write("<script>alert('Record Not Found')</script>");
    }
}

}

My Code In DBLayer.cs is the following

public class DBLayer

{

    public SqlConnection _SqlConnection;

    public SqlCommand _SqlCommand;

    public SqlDataAdapter _SqlDataAdapter;

    public SqlDataReader _SqlDataReader;

    public DataSet _DataSet;

public DBLayer()
{
}
    public int InsertEditDelete(string query)
    {
        int i;
        try
        {

            _SqlConnection = new SqlConnection("server=.;user id=sa;password=sa;initial catalog=RealEstate");
            _SqlConnection.Open();
            _SqlCommand = new SqlCommand(query, _SqlConnection);
            i = _SqlCommand.ExecuteNonQuery();

        }
        catch (Exception ied)
        {
            i = -1;


        }
        finally
        {

            _SqlConnection.Dispose();
            _SqlCommand.Dispose();
            _SqlConnection.Close();

        }
        return i;
    }
    public DataSet DataAdapter(string query, string tname)
    {
        try
        {
            _SqlConnection = new SqlConnection("server=.;user id=sa;password=sa;initial catalog=RealEstate");
            _SqlConnection.Open();
            _SqlDataAdapter = new SqlDataAdapter(query, _SqlConnection);

            _DataSet = new DataSet();
            _SqlDataAdapter.Fill(_DataSet,tname);


        }
        catch (Exception ds)
        {
            _DataSet  = null;

        }
        finally
        {
            _SqlConnection.Dispose();               
            _SqlConnection.Close();
        }
        return _DataSet;
    }
    public SqlDataReader SelectMethod(string query)
    {
        try
        {
            _SqlConnection = new SqlConnection("server=.;user id=sa;password=sa;initial catalog=RealEstate");
            _SqlConnection.Open();
            _SqlCommand = new SqlCommand(query, _SqlConnection);
           _SqlDataReader  = _SqlCommand.ExecuteReader();
        }
        catch (Exception sm)
        {
         _SqlDataReader = null;

        }
        return _SqlDataReader;
    }  

}

when I run the website it's exploding at the following point, if (dr.Read()) [Error Msg: Object reference not set to an instance of an object.]

what am I missing? i'm kind of a beginner :P help to solve this issue will run the site wonderfuly thanks

Answer 1

I saw at least 4 problems in your code 1. you silencely swallow your exception in your code, doesn't make any sence.

try
    {
        _SqlConnection = new SqlConnection("server=.;user id=sa;password=sa;initial catalog=RealEstate");
        _SqlConnection.Open();
        _SqlCommand = new SqlCommand(query, _SqlConnection);
       _SqlDataReader  = _SqlCommand.ExecuteReader();
    }
    **catch (Exception sm)
    {
     _SqlDataReader = null;
    }**

2. you disposed your connection before you close it, the exception will be throwed in the finally.

finally
    {
        _SqlConnection.Dispose();               
        _SqlConnection.Close();
    }

3. it's not a best prectice to swallow the exception and do nothing, you lost your stacktrace.

4 set _sqlconnection and those unmanaged object to be globle variable without implement IDisposable is not good.

finally set a break point on the line of code where exception throwed and try to debug your code yourself.

Answer 2

I don't know what is odb in your code, but the point is that SelectMethod is returning null.

After your edit, it looks like the culprit is the try/catch block in your SelectMethod: probably an exception is being raised, and since you just do nothing with it, you cannot understand what's going wrong:

try {
    // do DB stuff...
}
catch (Exception sm) { // What does this exception contain???
    _SqlDataReader = null;
}

Try stepping in your code with the debugger and see what the exception is. If you cannot do that, just remove the catch block: as you can see, it's only hiding the failure of the cause, but it's not making the code magically work :)