Question

I have a text file in which I am storing entries for an address book.
The layout is like so:

Name:
Contact:
Product:
Quantity:

I have written some linq code to grab the name plus the next four lines, for a search by name feature.
I also want to be able to search by contact.
The challenge is to match the contact info, grab the next 3 lines, and also grab the line prior to the match.
That way if Search By Contact is used, the full list of info will be returned.

  private void buttonSearch_Click(object sender, EventArgs e)
    {
            string[] lines = File.ReadAllLines("C:/AddressBook/Customers.txt");
            string name = textBoxSearchName.Text;
            string contact = textBoxContact.Text;

            if (name == "" && contact == "")
            {
                return;
            }

            var byName = from line in lines
                         where line.Contains(name)
                         select lines.SkipWhile(f => f != line).Take(4);

            //var byContact = from line in lines
            //                where line.Contains(name)
            //                select lines.SkipWhile(f => f != name).Take(4);


            if (name != "")
            {
                foreach (var item in byName)
                    foreach (var line in item) { listBox2.Items.Add(line); }

                listBox2.Items.Add("");
            }

            //if (contact != "")
            //{
            //    foreach (var item in byContact)
            //        foreach (var line in item) { listBox2.Items.Add(line); }

                //listBox2.Items.Add("");
            }
    }

Answer 1

Firstly i would recommend changing your data storage approach if you can.

Secondly i would recommend reading the file into an object, something like this:

public class Contact
{

    public string Name {get; set;}
    public string Contact {get; set;}
    public string Product {get; set;}
    public int Quantity {get; set;}
}
...
public IEnumerable<Contact> GetContacts()
{
    //make this read line by line if it is big!
    string[] lines = File.ReadAllLines("C:/AddressBook/Customers.txt");
    for (int i=0;i<lines.length;i += 4)
    {
        //add error handling/validation!
        yield return new Contact()
        {
              Name = lines[i],
              Contact = lines[i+1],
              Product = lines[i+2],
              Quantity = int.Parse(lines[i+3]
         };
    }
}
private void buttonSearch_Click(object sender, EventArgs e)
{
    ...
    var results = from c in GetContacts()
                 where c.Name == name ||
                       c.Contact == contact
                 select c;
    ...
}