Staff name, surname and telephone no informations

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I want to write with C# without database. First Textbox has got name,second surname and third tel no.
Button1 keeps information from 3 textboxes in memory and when I press button2 I will see the information in the listbox

I get NullReferencesException error when I write below

What I have tried:

C#

class Class1
    {
        public string[] information;
        public int counter=1;
        public string[] solution(string name, string surname, string telno)
        {
            information = new string[counter];
            
            for (int i = 0; i < information.Length; i++)
            {
                information[i] += name + surname + telno;
                counter++;
            }
            return information;
        }
        public string[] show()
        {
            string[] information= new string[counter];

            for (int i = 0; i < information.Length; i++)
            {
                information[i] += information[i].ToString();
                counter++;
            }
            return information;
        }
    }


private void button1_Click(object sender, EventArgs e)
        {
           
            Class1 yeni = new Class1();
            string[] dizi = yeni.solution(textBox1.Text, textBox2.Text, textBox3.Text);
            string metin = "";
            for (int i = 0; i < dizi.Length; i++)
                metin += dizi[i];
           
        }

        private void button2_Click(object sender, EventArgs e)
        {
          
            Class1 yeni = new Class1();
            listBox1.Items.Add(yeni.show());
           
        }

Posted 8-Nov-17 3:41am

GamzeAytac

Updated 8-Nov-17 4:15am

CPallini

v2

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Comments

Karthik_Mahalingam 8-Nov-17 10:04am

which line ?

2 solutions

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OriginalGriff · Answer 1 · 2017-11-08T04:02:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Richard MacCutchan · Answer 2 · 2017-11-08T04:15:00

The problem is that you create a new instantiation of Class1 in each of your button handlers so the information is lost. You need to instantiate your object outside of those handlers, something like:

C#

Class1 yeni;

private void button1_Click(object sender, EventArgs e)
{
    yeni = new Class1();
    string[] dizi = yeni.solution(textBox1.Text, textBox2.Text, textBox3.Text);
    string metin = "";
    for (int i = 0; i < dizi.Length; i++)
        metin += dizi[i];

}

private void button2_Click(object sender, EventArgs e)
{
    listBox1.Items.Add(yeni.show());

}

Staff name, surname and telephone no informations

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