Problem loading text file data as Listbox selected index is changed

Question

2.00/5 (1 vote)

See more:

hi all
i have 2 list boxes in form.
list_number (displaying text file name)
list_position (displaying data of file selected in list_nomber)
but i m getting exception on selected index changed event exception is below

System.ArgumentNullException: Value cannot be null.
Parameter name: item
at System.Windows.Forms.ListBox.ObjectCollection.AddInternal(Object item)
at System.Windows.Forms.ListBox.ObjectCollection.Add(Object item)
at WindowsFormsApplication1.Form1.list_nomber_SelectedIndexChanged(Object sender, EventArgs e) in E:\videoPlayer\videoPlayer\Form1.cs:line 395

line 395 is this

C#

listPosition = objReader.ReadLine();

and code is this

C#

private void list_nomber_SelectedIndexChanged(object sender, EventArgs e)
        {
            string listPosition="abc";
            list_position.Items.Clear();
            string file = "e:\\" + list_nomber.Text + ".txt";
            System.IO.StreamReader objReader;
            objReader = new System.IO.StreamReader(file);
            while (objReader.ReadLine() != null)
            {

                listPosition = objReader.ReadLine();
                list_position.Items.Add(listPosition);
            }
            objReader.Close();
        }

Posted 6-Dec-13 18:53pm

mehdilahori

Add a Solution

Comments

Sergey Alexandrovich Kryukov 7-Dec-13 1:08am

In what line?
—SA

1 solution

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)

BillWoodruff · Accepted Answer · 2013-12-06T19:38:00

Your problem is that you are doing an extra ReadLine in the 'while loop test: so, when you've read the last of the file inside the loop, the last 'while loop test tries to "eat" null. You are going to get every other line in the file until you reach the error condition.

Try this:

C#

using System.IO;

//somewhere in a method
string file = @"e:\" + list_nomber.Text + ".txt";

string currentLine;

list_position.Items.Clear();

using (StreamReader objReader = new StreamReader(file))
{
    while ((currentLine = objReader.ReadLine()) != null)
    {
        list_position.Items.Add(currentLine);
    }

    objReader.Close();
}