null reference exception while assigning values to objects in array of objects

Question

I'm getting a null reference exception and i don't know how to solve it or why it even happens.

private void editThisToolStripMenuItem_Click(object sender, EventArgs e)
{
    if (dataGridView1.SelectedRows.Count <= 1)
    {
        Form2 f2 = new Form2(dataGridView1.SelectedRows[0].Cells[1].Value.ToString(), Convert.ToInt32(dataGridView1.SelectedRows[0].Cells[2].Value));
        f2.ShowDialog();
        textBox2.Text = textBox1.Text.Replace(f2.oldtext, f2.newtext);
        this.dataGridView1.SelectedRows[0].Cells[3].Value = f2.newtext;
        this.dataGridView1.SelectedRows[0].Cells[3].Style.BackColor = Color.IndianRed;
    }
    else
    {
        ONOType[] ono = new ONOType[this.dataGridView1.SelectedRows.Count];
        int indexerr = 0;
        foreach (DataGridViewRow r in dataGridView1.SelectedRows)
        {
            ono[indexerr].newtext = this.dataGridView1.SelectedRows[indexerr].Cells[3].Value.ToString(); //null expection at ono[indexerr].newtext
            ono[indexerr].oldtext = this.dataGridView1.SelectedRows[indexerr].Cells[1].Value.ToString();
            ono[indexerr].offset = Convert.ToInt32(dataGridView1.SelectedRows[indexerr].Cells[0].Value);
            indexerr++;
        }
        Form3 f3 = new Form3(ono);
        f3.ShowDialog();
        indexerr = 0;
        for (int i = 0; i < dataGridView1.SelectedRows.Count; i++)
        {
            textBox2.Text = textBox1.Text.Replace(f3.nt[i].oldtext, f3.nt[i].newtext);
            this.dataGridView1.SelectedRows[i].Cells[3].Value = f3.nt[i].newtext;
            this.dataGridView1.SelectedRows[i].Cells[3].Style.BackColor = Color.IndianRed;
        }
    }
}

and here is the ono class

namespace IEditor
{
    public class ONOType
    {
        public string oldtext { get; set; }
        public string newtext { get; set; }
        public int offset { get; set; }
    }
}

The problem starts at:

ONOType[] ono = new ONOType[this.dataGridView1.SelectedRows.Count];

It defines the new array of this class type all to null which something I don't want and maybe it's caused by the keyword "new" and without the "new" keyword i get comp. error for assigning value to that objects in this array.

What i did try was adding a ctor to this class to assign default values for each of this array members of members (aka assign values for oldtext/newtext/offset) on deceleration but still objects in this objects array are null and i did try to do the same at the get/set properties , but i still failed.

Please add an explanation with the solution.

SelectedRows.Count <= 1 did you mean SelectedRows.Count >= 1? — 500 - Internal Server Error
– 500 - Internal Server Error, Commented Mar 15, 2013 at 0:21
no , i meant selected rows count <= 1 , it means if the selected items are only one or less to apply the first code which edit only 1 object but the problem is at the multiple selections which to why i'm having that problem at the array of objects — Andrew
– Andrew, Commented Mar 15, 2013 at 0:23
If your selected count is zero you then go on to read the first selected item, which is going to be null, was my point. — 500 - Internal Server Error
– 500 - Internal Server Error, Commented Mar 15, 2013 at 0:25
yes that's right , thank you :) but that doesn't cause problems for now and ill add more checks when i get it to work :) — Andrew
– Andrew, Commented Mar 15, 2013 at 0:27
There are so many referneces that can be null in the code. You need to debug it to find the exact place. Enable the "thrown" option for managed exception and run it through the debugger. — Brian Rasmussen
– Brian Rasmussen, Commented Mar 15, 2013 at 2:04

Stainy · Accepted Answer · 2013-03-15 02:11:01Z

3

You are creating a new array of ONOType references with:

    ONOType[] ono = new ONOType[this.dataGridView1.SelectedRows.Count];

But none of the actual ONOType objects are created. It's just an array of variables that reference nothing yet.

When you try to assign ono[indexerr].newtext the element at ono[indexerr] is a null reference.

If you did:

    ono[indexerr] = new ONOType();
    ono[indexerr].newtext = this.dataGridView1.SelectedRows[indexerr].Cells[3].Value.ToString();

I think it would work.

edited Mar 15, 2013 at 2:11

answered Mar 15, 2013 at 2:03

Stainy

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2 Comments

Andrew Over a year ago

thanks for explaining that point to me :) it worked out , thank you so much :)

ye-olde-dev Over a year ago

I wish I could up vote this a thousand times. Literally been trying to figure this out for three days :[

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