Object reference not set to an instance of an object.how to solve this error?

Question

1.00/5 (1 vote)

See more:

Hi, I am learning basic developer,so I dont have much info how to handle this error.. I am getting "Object reference not set to an instance of an object" error... I am simply trying to view the values of object of 1st form to another form..
My code for form1 is:

public partial class Form1 : Form
{
public String Username
{
get{return Username_Box.Text;}
set{Username_Box.Text= value;}
}
public Form1()
{
InitializeComponent();
}

public void button1_Click(object sender, EventArgs e)
{
Form2 Form2_Interface = new Form2();
Form2_Interface.Form1_Interface = this;

Form2_Interface.Show();
}
}

And code for form2 is:
public partial class Form2 : Form
{
public Form1 Form1_Interface;

public Form2()
{
InitializeComponent();

this.label1.Text = "Hi" + Form1_Interface.Username + "!";
}

}

When I use break pouints I am getting null value for "Form1_Interface.Username" during debuging.. But How Is it possible when I am already giving some text to "Username_Box"...

Posted 30-May-13 16:51pm

Member 10027343

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

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

Sergey Alexandrovich Kryukov · Answer 1 · 2013-05-30T17:37:00

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

Bernhard Hiller · Answer 2 · 2013-05-30T21:22:00

Because you do that in the contructor of Form2, before you set the reference to form1. Just look at the steps: You start with
Form2 Form2_Interface = new Form2();
When new Form2() is executed, you do
this.label1.Text = "Hi" + Form1_Interface.Username + "!";
but only afterwards you tell Form2 where to find Form1:
Form2_Interface.Form1_Interface = this;
There are several ways to solve that:
you could create a parameterized constructor and call Form2 Form2_Interface = new Form2(this);
you could move the setting of the label's text to the Load or Shown event of Form2.
you could change the property set code for the Form1_Interfaceproperty of Form2 and set the label's text there.

Object reference not set to an instance of an object.how to solve this error?

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0