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BOOK: Professional ASP.NET 4 : in C# and VB
This is the forum to discuss the Wrox book Professional ASP.NET 4 in C# and VB by Bill Evjen, Scott Hanselman, Devin Rader; ISBN: 9780470502204
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  #1 (permalink)  
Old October 11th, 2011, 06:19 AM
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Default Listing 1-10 NullReferenceException was unhandled by

Hello All,

I am getting the error NullReferenceException was unhandled by user code on the Listing I.10.

The exception occurs on the TextBox1 object.

My code is as follows.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Listing1-10.aspx.cs" Inherits="WebApplication1.Listing1_10" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, System.EventArgs e)
{
TextBox pp_TextBox1;
Calendar pp_Calendar1;

pp_TextBox1 = (TextBox)PreviousPage.FindControl("TextBox1");
pp_Calendar1 = (Calendar)PreviousPage.FindControl("Calendar1");

Label1.Text = "Hello " + pp_TextBox1.Text + "<br />" + "Date Selected " +
pp_Calendar1.SelectedDate.ToShortDateString();
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:Label ID="Label1" runat="server"></asp:Label>
</form>
</body>
</html>

What is a null reference exception?

Why does it apply to the TextBox1 object?

Any help would be most appreciated.

Kind Regards

Thomas
  #2 (permalink)  
Old February 14th, 2012, 05:29 PM
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Default Previous Page

Hi there

I think you're running this page directly. the source of the NullException in your sample refers to PreviousPage. it does not contains a control named 'TextBox1' so >>> (TextBox)PreviousPage.FindControl("TextBox1"); <<< return null. if you write:
string msg = ((TextBox)PreviousPage.FindControl("TextBox1")).Te xt;
You'll got the error here. NullReferenceException
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Last edited by irProject; February 14th, 2012 at 05:32 PM.
 


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