Listview selected item value - not Index

Question 1

In order to find the right object to update you first need to find the object in the People collection that matches the object selected in the ListView.

Person i = People.FirstOrDefault(p => p.Name == ((ListView) sender).SelectedItems[0].Text);
PopulateEditData(i); // refer below for method...

This can only work if you have the MultiSelect property set to false, otherwise you will need to get the right item from the collection of selected items.

As seen here: http://msdn.microsoft.com/en-us/library/system.windows.forms.listview.selecteditems(v=vs.110).aspx

Once you have the right Person object, you will be able to retrieve and display the objects details in the text boxes:

private void PopulateEditData(Person selectedPerson)
{
    textBox1.Text = selectedPerson.Name;
    textBox2.Text = selectedPerson.Hometown;
    textBox3.Text = selectedPerson.Address;
    textBox4.Text = selectedPerson.Phone;
    textBox5.Text = selectedPerson.Email;
    textBox6.Text = selectedPerson.AdditionalInfo;
    dateTimePicker1.Value = selectedPerson.Birthday;
    textBox1.ReadOnly = true;
    textBox2.ReadOnly = true;
    textBox3.ReadOnly = true;
    textBox4.ReadOnly = true;
    textBox5.ReadOnly = true;
    textBox6.ReadOnly = true;
    dateTimePicker1.Enabled = false;
    toolStripButton5.Enabled = true;
}

I would also suggest setting the selectPerson as a property of your form or one of the classes available to it so it is a little easier to edit and save the data on the object.

For the removal part of the problem, use the SelectedPerson property for the item to be removed.

private void button1_Click(object sender, EventArgs e)
    {
        if (SelectedPerson != null)
        {
            People.Remove(SelectedPerson);
            this.listView1.Items.Clear();
            foreach (var person in People)
            {
                this.listView1.Items.Add(person.ToString());
                this.listView1.Sorting = SortOrder.Ascending;
            }
            this.listView1.Refresh();
            this.button1.Enabled = false;
        }
    }

Question 2

Thank you for your answer.

Anyway, I have managed to solve the problem in the following way:

1) I have added:

private Person FindPerson(string name)
    {
        return people.Find(x => x.Name == name);
    }

2) I have replaced:

people[listView1.SelectedItems[0].Index]

with "person", where person is:

Person person = FindPerson(listView1.SelectedItems[0].Text);

where FindPerson is:

private Person FindPerson(string name)
{
    return people.Find(x => x.Name == name);
}

Anyway, I keep getting error when I try to remove the last remaining contact. Even when I try to select it, not just remove it. Here you can take a look what error is about:

IMAGE: http://s24.postimg.org/ls4nak6et/Kruzeri.png

So, this is how it looks like now:

private void listView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (listView1.SelectedItems.Count == 0) return;
        Person person = FindPerson(listView1.SelectedItems[0].Text);
        textBox1.Text = person.Name;
        textBox2.Text = person.Hometown;
        textBox3.Text = person.Address;
        textBox4.Text = person.Phone;
        textBox5.Text = person.Email;
        textBox6.Text = person.AdditionalInfo;
        dateTimePicker1.Value = person.Birthday;
        textBox1.ReadOnly = true;
        textBox2.ReadOnly = true;
        textBox3.ReadOnly = true;
        textBox4.ReadOnly = true;
        textBox5.ReadOnly = true;
        textBox6.ReadOnly = true;
        dateTimePicker1.Enabled = false;
        toolStripButton5.Enabled = true;
    }

and Save button:

private void toolStripButton1_Click(object sender, EventArgs e)
    {
         if (listView1.SelectedItems.Count > 0)
        {
            Person person = FindPerson(listView1.SelectedItems[0].Text); 
            person.Name = textBox1.Text;
            person.Hometown = textBox2.Text;
            person.Address = textBox3.Text;
            person.Phone = textBox4.Text;
            person.Email = textBox5.Text;
            person.Birthday = dateTimePicker1.Value;
            person.AdditionalInfo = textBox6.Text;
            listView1.SelectedItems[0].Text = textBox1.Text;
            textBox1.ReadOnly = true;
            textBox2.ReadOnly = true;
            textBox3.ReadOnly = true;
            textBox4.ReadOnly = true;
            textBox5.ReadOnly = true;
            textBox6.ReadOnly = true;
            dateTimePicker1.Enabled = false;
        }
        else
        {
            MessageBox.Show("Nothing is selected ", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
        UserCount();
    }

Question 3

Your function returns null because no item is selected. So person is of course null. You should handle this in your FindPerson-Function.