NullReferenceException: Object reference not set to an instance of an object #2

Question

Error shown on the website. Im using asp net visual C# webform, access data source (MS access) When I click on Add to Cart button on productdetails.aspx

Line 41:         int intOrderNo = (int)Session["sOrderNo"];
Line 42:         string strUnitPrice = (string)Session["sUnitPrice"];
Line 43:         decimal decUnitPrice = decimal.Parse(strUnitPrice);

For myOrder table in Ms Access There is oOrderNo, oDate, oUserName, oPaymentMode, oStatus,

 protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
    // test to remind customer to login first
    if ((string)Session["sFlag"]!="T")
    {
        Type csType = this.GetType();
        ClientScript.RegisterStartupScript(csType, "Error", scriptErrorLogin);
    }

    // Connect to database  
    OleDbConnection mDB = new OleDbConnection();
    mDB.ConnectionString = "Provider = Microsoft.ACE.OLEDB.12.0;Data source=" + Server.MapPath("~/App_Data/webBase.accdb");
    mDB.Open();
    OleDbCommand cmd;
    DetailsViewRow row0 = DetailsView1.Rows[0];
    string strProductID = row0.Cells[1].Text;
    mDB.Close();

    // save as session variables
    Session["sProductID"] = strProductID;
    DetailsViewRow row4 = DetailsView1.Rows[4];
    Session["sUnitPrice"] = row4.Cells[1].Text;


    int intOrderNo = (int)Session["sOrderNo"];
    string strUnitPrice = (string)Session["sUnitPrice"];
    decimal decUnitPrice = decimal.Parse(strUnitPrice);
    string strSQL = "INSERT INTO orderItems(uOrderNo, uProductID, uUnitPrice)" + "VALUES(@eOrderNo, @eProductID, @eUnitPrice)";
    cmd = new OleDbCommand(strSQL, mDB);
    cmd.Parameters.AddWithValue("@eOrderNo", intOrderNo);
    cmd.Parameters.AddWithValue("@eProductID", strProductID);
    cmd.Parameters.AddWithValue("@eUnitPrice", decUnitPrice);

    mDB.Open();
    cmd.ExecuteNonQuery();
    mDB.Close();

    Response.Redirect("ShoppingCart.aspx");

Kindly check the session variable values and add the full stack trace — Sureshkumar Panneerselvan
– Sureshkumar Panneerselvan, Commented Jan 20, 2014 at 4:05
Welcome to Stack Overflow! Almost all cases of NullReferenceException are the same. Please see "What is a NullReferenceException in .NET?" for some hints. — John Saunders
– John Saunders, Commented Jan 20, 2014 at 4:05
Line 42: string strUnitPrice = (string)Session["sUnitPrice"]; can be Session["sUnitPrice"].ToString() — Zigma
– Zigma, Commented Jan 20, 2014 at 4:11
@Kayzel Moo : I see that you are trying to cast the value which is stored in a session. in this case the only reason why you get Object reference error would be because session is empty or does not exists. — Venkatesh Ellur
– Venkatesh Ellur, Commented Jan 20, 2014 at 5:40

Community · Accepted Answer · 2017-05-23 11:47:12Z

1

Try this

Line 41:         int intOrderNo = Session["sOrderNo"] == DBNull.Value ? 0 : (int)Session["sOrderNo"];
Line 42:         string strUnitPrice = Session["sUnitPrice"] == DBNull.Value ? string.Empty : (string)Session["sUnitPrice"];

null Vs DBNull.Value

edited May 23, 2017 at 11:47

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answered Jan 20, 2014 at 4:36

Vignesh Kumar A

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4 Comments

Marcus Moo Over a year ago

Should i Use null or dnull.value?

Vignesh Kumar A Over a year ago

use dbnull.value. refer my link. mark useful if its helped you

Marcus Moo Over a year ago

And spidercode the guy above uses != while u uses == , the difference is?

Marcus Moo Over a year ago

actually there's not a need to do dbnull for price i think?

HardikS · Accepted Answer · 2014-01-20 04:12:54Z

0

Try below code :

Line 41:         int intOrderNo = Session["sOrderNo"] == null ? 0 : (int)Session["sOrderNo"];
Line 42:         string strUnitPrice = Session["sUnitPrice"] == null ? string.Empty : (string)Session["sUnitPrice"];
Line 43:         decimal decUnitPrice = string.IsNullOrWhiteSpace(strUnitPrice) ? 0 : decimal.Parse(strUnitPrice);

answered Jan 20, 2014 at 4:12

HardikS

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2 Comments

Marcus Moo Over a year ago

the guy below use dbnull, so which do i follow

Marcus Moo Over a year ago

Guys so far i think just int intOrderNo = Session["sOrderNo"] == null ? 0 : (int)Session["sOrderNo"]; WORKS haven't tried kumar dbnull below. Thanks all for help :)

Sureshkumar Panneerselvan · Accepted Answer · 2014-01-20 04:13:08Z

0

Just check that if Session variable is Null-

 if( Session["sOrderNo"] != null && all the session variables )
{
     //Now check your condition here
}
else {
       //Perform any operation
    }

answered Jan 20, 2014 at 4:13

Sureshkumar Panneerselvan

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null Vs DBNull.Value

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