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, Jan 20 '14 at 04:05
Welcome to Stack Overflow! Almost all cases of `NullReferenceException` are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Jan 20 '14 at 04:05
`Line 42: string strUnitPrice = (string)Session["sUnitPrice"];` can be `Session["sUnitPrice"].ToString()` — Zigma, Jan 20 '14 at 04:11
@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, Jan 20 '14 at 05:40
Before you retrieve and cast value from session, Check for the session is null or not. See my answer for the same. — SpiderCode, Jan 20 '14 at 06:03
@VenkateshEllur I thank you all for your help. You all list different methods but I'm quite confused which to use — Marcus Moo, Jan 21 '14 at 01:36
@VenkateshEllur the error is wrong with int(intOrderNo = (int)Session["sOrderNo"]; most of the time it can work, sometimes it dont, so im confused. — Marcus Moo, Jan 21 '14 at 01:41
@Zigma the error is wrong with int(intOrderNo = (int)Session["sOrderNo"]; most of the time it can work, sometimes it dont, so im confused. — Marcus Moo, Jan 21 '14 at 01:41
@ssilas777 convert.tostring() don't work because you cant convert string to int — Marcus Moo, Jan 21 '14 at 01:44
(string)Session["sUnitPrice"]; - I was pointing this lines, as convert.tostring handles null values.BTW you can convert string("3") to int. — ssilas777, Jan 21 '14 at 04:49

score 1 · Answer 1 · edited May 23 '17 at 11:47

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 '17 at 11:47

Community

1
1

answered Jan 20 '14 at 04:36

Vignesh Kumar A

27,863
13
63
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Should i Use null or dnull.value? – Marcus Moo Jan 21 '14 at 01:33
use dbnull.value. refer my link. mark useful if its helped you – Vignesh Kumar A Jan 21 '14 at 01:40
And spidercode the guy above uses != while u uses == , the difference is? – Marcus Moo Jan 21 '14 at 01:45
actually there's not a need to do dbnull for price i think? – Marcus Moo Jan 21 '14 at 01:58

score 0 · Accepted Answer · answered Jan 20 '14 at 04:12

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 '14 at 04:12

SpiderCode

10,062
2
22
42

the guy below use dbnull, so which do i follow – Marcus Moo Jan 21 '14 at 01:43
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 :) – Marcus Moo Jan 21 '14 at 01:59

score 0 · Answer 3 · answered Jan 20 '14 at 04:13

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 '14 at 04:13

Sureshkumar Panneerselvan

749
6
22

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

3 Answers3

null Vs DBNull.Value

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