Error in report code in C#

Question

User639567535 posted

i try to get report when user click on update.. scanerio is there is edit button in gridview and also there is several records so when user click on this edit button then box appear furthermore there is several fields then user select report type from drop down now when user select report type and click on update button then report is display but when i debug error is occurred i try this code

protected void gvNR_NRListDevx_AfterPerformCallback(object sender, ASPxGridViewAfterPerformCallbackEventArgs e)
        {
            if (e.CallbackName == "STARTEDIT")
            {
                int index = ((ASPxGridView)sender).EditingRowVisibleIndex;
                //view state value with in page... in this code we get form id from gridview
                ViewState["FFID"] = ((ASPxGridView)sender).GetRowValues(((ASPxGridView)sender).FocusedRowIndex, "FormID");
                //get vechile id from gridview
                ViewState["VID"] = ((ASPxGridView)sender).GetRowValues(((ASPxGridView)sender).FocusedRowIndex, "VID");
                //get form datetime from gridview
                ViewState["DateTime"] = Convert.ToDateTime(((ASPxGridView)sender).GetRowValues(((ASPxGridView)sender).FocusedRowIndex, "DateTime"));


            }
            else if (e.CallbackName == "CANCELEDIT")
            {

            }
            else if(e.CallbackName == "UPDATEEDIT")
            {
                DateTime DateT = (DateTime)ViewState["DateTime"];
                string VehId = (string)ViewState["VID"];
                _sys = new clsDe_ComplainMaster();
                DataTable dtUpdated = _sys.SelectUpdatedNRtype(ViewState["FFID"].ToString(), VehId, DateT);

                if (dtUpdated.Rows[0]["NRType"].ToString() == "0002") 
                {
                    printgpsreport(DateT, VehId, "REPORT1.rpt");
                }
                else if (dtUpdated.Rows[0]["NRType"].ToString() == "0011")
                {
                    printgpsreport(DateT, VehId, "REPORT2.rpt");
                }



 public DataTable SelectUpdatedNRtype(string FormID , string VEhID, DateTime DateT)
    {
        string strSql = "select NRType from NR_NRType_LogHistory where FormID = '" + FormID + "' ANd VehicleID = '" + VEhID + "' AND NRDate = '" + DateT + "'";

        return this.GetQueryData(strSql);

    }

public DataSet getreport()
    {
        DataSet ds;
        try
        {
            SqlParameter[] Params = 
            { 
                new SqlParameter("@datetime",SqlDbType.DateTime),
                new SqlParameter("@VehID",SqlDbType.VarChar)

        };

            if ( datetime != null)
            {
                Params[0].Value = datetime;

            }
            else
            {
                Params[0].Value = DBNull.Value;
            }

            if (VehID != null)
            {
                Params[1].Value = VehID;
            }
            else
            {
                Params[1].Value = DBNull.Value;
            }

            ds = GetDataSet("sp_gps_report", Params);

            return ds;
        }
        catch (Exception ex)
        {
            throw new Exception(ex.Message);
        }

    }

ERROR IS OCCURED ON THIS LINE

DateTime DateT = (DateTime)ViewState["DateTime"];

An exception of type 'System.NullReferenceException' occurred in ERP.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.

any help please

Answer 1

User1577371250 posted

Hi,

It states that your ViewState is NULL.

if(ViewState["DateTime"] != null)
{
    DateTime DateT = (DateTime)ViewState["DateTime"];
}

Answer 2

User-434868552 posted

@Bakhtawar As...

    else if(e.CallbackName == "UPDATEEDIT")
    {
*       DateTime DateT = (DateTime)ViewState["DateTime"];

at the very least, you should set a break point on the above statement.

An exception of type 'System.NullReferenceException' occurred in ERP.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.

ViewState["DateTime"] is null ... your goal is to determine WHY ViewState["DateTime"] is null.

whenever  ViewState["DateTime"] is null, you will experience a 'System.NullReferenceException'.

Bakhtawar As..., you also need to make your code more robust with a try/catch:

    else if(e.CallbackName == "UPDATEEDIT")
    {
        try
        {
            DateTime DateT = (DateTime)ViewState["DateTime"];
        }
        catch (System.NullReferenceException nullDateTime)
        {
            // code to appropriately handle NullReferenceException type of exception 
        }
        catch (Exception unknown)
        {
            // code to appropriately handle any other type of exception 
        }

EDIT:

you have a secondary problem:

DateTime example = (DateTime)"2016-04-28"; // CS0030 Cannot convert type 'string' to 'System.DateTime'

i'm guessing that when ViewState["DateTime"] is not null, it's likely to be a System.String type.

for that reason, your probably want your code to be similar to this:

if (String.IsNullOrWhiteSpace(ViewState["DateTime"]))
{
   // handle invalid date/time error
}
else
{
  // use DateTime.TryParse to convert ViewState["DateTime"] to System.DateTime
}

END EDIT.

Answer 3

User639567535 posted

Hi,

It states that your ViewState is NULL.

if(ViewState["DateTime"] != null)
{
    DateTime DateT = (DateTime)ViewState["DateTime"];
}

thank you for your reply 

when i try this it shows me error on this line 

if (dtUpdated.Rows[0]["NRType"].ToString() == "0002")
{
printgpsreport(DateT, VehId, "report1.rpt");
}

 The name 'DateT' does not exist in the current context 

Answer 4

User-434868552 posted

@Bakhtawar As...

Please study my reply, above; note the edit.

Regarding your current reply to Lokesh B R, you need to ensure that you do not lose scope:

Boolean goodDateTime = false;  // for DateTime.TryParse
DateTime DateT;                // out parameter for DateTime.TryParse
if (String.IsNullOrWhiteSpace(ViewState["DateTime"]))
{
   // handle invalid date/time error
}
else
{
    // use DateTime.TryParse to convert ViewState["DateTime"] to System.DateTime
}
if(goodDateTime)
{
    // then you can safely use the value of DateT
}

Answer 5

User303363814 posted

There is no entry in the ViewState called "DateTime".  Where is the code that creates it?