Error when I click the print button

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Hello.
I have a web form that a user can input data on the form and save it to the database. The user can also print a report of the data that they just entered. Well, when the user clicks the print button it calls for another page to show the report. When that page pops up this error is in it:

HTML

 Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[NullReferenceException: Object reference not set to an instance of an object.]
   FinancialProfileFormA.Page_Load(Object sender, EventArgs e) in C:\Users\khopkins\Documents\Visual Studio 2010\Projects\SACSCOCLogin1.1\SACSCOCLogin1.1\FinancialProfileFormA.aspx.cs:45
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +91
   System.Web.UI.Control.LoadRecursive() +74
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2207

Here is the code for the Print Button:

C#

using System;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Text;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Configuration;
using System.Drawing.Printing;
using System.IO;
using System.Web.SessionState;
using CrystalDecisions.CrystalReports.Engine;
using CrystalDecisions.Shared;

public partial class FinancialProfileFormA : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }

protected void ButtonPrint_Click(object sender, EventArgs e)
    {
        TextBoxINST_ID.Text = Session["inst_id"].ToString();
        ClientScript.RegisterStartupScript(this.GetType(), "onclick", "<script language=javascript>window.open('ReportFormA.aspx','PrintMe','height=650px,width=800px,scrollbars=1');</script>");
    }

Here is the code for the page the print button calls:

C#

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using CrystalDecisions.Web;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.WebControls;
using CrystalDecisions.CrystalReports.Engine;
using CrystalDecisions.Shared;
using CrystalDecisions.Windows.Forms;
using CrystalDecisions.ReportSource;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Xml.Linq;
using System.Web.SessionState;


namespace SACSCOCLogin1._1
{
    public partial class ReportFormA : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            TextBoxINST_ID.Text = Session["inst_id"].ToString();
            CrystalReportViewer1.Visible = true;

            ReportDocument CrystalReport = new ReportDocument();
            ParameterField paramField = new ParameterField();
            ParameterFields paramFields = new ParameterFields();
            ParameterDiscreteValue paramDiscreteValue = new ParameterDiscreteValue();

            paramField.Name = "inst_id";
            paramField.CurrentValues.Clear();
            paramDiscreteValue = new ParameterDiscreteValue();
            paramDiscreteValue.Value = TextBoxINST_ID.Text;
            paramFields.Add(paramField);
            CrystalReportViewer1.ParameterFieldInfo = paramFields;

            CrystalReport.Load(Server.MapPath("~/Reports/FormAReport.rpt"));
            string sessiontype = TextBoxINST_ID.Text;
            CrystalReport.SetParameterValue("inst_id", TextBoxINST_ID.Text);

            string sessionid = TextBoxINST_ID.Text;
            CrystalReport.SetParameterValue("inst_id", TextBoxINST_ID.Text);
            //CrystalReport.Refresh();
            CrystalReport.SetDatabaseLogon("Adminr", "master22", @"SQL", "Hot");
            CrystalReportViewer1.ReportSource = CrystalReport;
        }
    }
}

This is the code for the Print Helper page:

C#

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Text;
using System.Web.SessionState;

public class PrintHelper
{
    public PrintHelper()
    {
    }

    public static void PrintWebControl(Control ctrl)
    {
        PrintWebControl(ctrl, string.Empty);
    }

    public static void PrintWebControl(Control ctrl, string Script)
    {
        StringWriter stringWrite = new StringWriter();
        System.Web.UI.HtmlTextWriter htmlWrite = new System.Web.UI.HtmlTextWriter(stringWrite);
        if (ctrl is WebControl)
        {
            Unit w = new Unit(100, UnitType.Percentage); ((WebControl)ctrl).Width = w;
        }
        Page pg = new Page();
        pg.EnableEventValidation = false;
        if (Script != string.Empty)
        {
            pg.ClientScript.RegisterStartupScript(pg.GetType(), "PrintJavaScript", Script);
        }
        HtmlForm frm = new HtmlForm();
        pg.Controls.Add(frm);
        frm.Attributes.Add("runat", "server");
        frm.Controls.Add(ctrl);
        pg.DesignerInitialize();
        pg.RenderControl(htmlWrite);
        string strHTML = stringWrite.ToString();
        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.Write(strHTML);
        HttpContext.Current.Response.Write("<script>window.print();</script>");
        HttpContext.Current.Response.End();
    }
}

How can I fix this? What did I do wrong?

Posted 25-Feb-14 12:47pm

Computer Wiz99

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Comments

Sergey Alexandrovich Kryukov 25-Feb-14 19:52pm

In what line?
—SA

2 solutions

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Abhinav S · Answer 1 · 2014-02-25T16:05:00

Solution 2

The session variable Session["inst_id"].ToString() should contain a value before you typecase it to a string.

Posted 25-Feb-14 16:05pm

Abhinav S

Comments

Sergey Alexandrovich Kryukov 25-Feb-14 23:06pm

5ed.
—SA

Abhinav S 25-Feb-14 23:22pm

Thank you SA.

Sergey Alexandrovich Kryukov · Answer 2 · 2014-02-25T13:53:00

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA