Question

I am using WinForms/VS2010 c# to create a listview with 12 columns and 8 rows. Here is the snippet from the WinForms auto-coded file:

    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
        this.listView1 = new System.Windows.Forms.ListView();
       .....
    } 

Then, in the Form1.cs file, I have the following method:

    // in my form1.cs file
    public void listView1_Populate()
    {
        var columnIndex = listView1.Columns[2].Index;
        int counter = 0;

        foreach (ListViewItem item in listView1.Items)
        {
             if (item.SubItems[columnIndex].Text == "2")
             {
                 counter += 100;
                 item.SubItems[columnIndex].Text = counter.ToString(); 
             }
        }
    }

But I get the Object reference not set to an instance of an object exception when the code hits the line: var columnIndex = listView1.Columns[2].Index;

What am I doing wrong (other than trying to learn c# at age 54!)?

Answer 1

Its not clear from your question what is null referenced. But if you add the following before this line var columnIndex = listView1.Columns[2].Index; you might get a clearer understanding of whats going wrong.

if (listView1 == null)
    throw new Exception("listView1 is null");
if (listView1.Columns == null)
    throw new Exception("Columns is null");
if (listView1.Columns.Length < 3)
    throw new Exception("Columns length is out of range");